III.B. DIFFERENTIAL LEVELING TO CGPS STATIONS
Introduction
A project was undertaken by the California Spatial Reference Center (CSRC) to establish a
North American Vertical Datum of 1988 (NAVD88) differential elevation on a selection of
continuous GPS (CGPS) stations that are part of the Southern California Integrated GPS
Network (SCIGN) array. (Further work is currently being done in other areas of the State
but this section will concentrate on the first leveling project completed, which was in
Southern California.) The purpose of this project was to establish an orthometric height on
the base of the preamplifier of the antenna (BPA) and the geodetic reference mark (GRM) at
each selected station which would then be used as vertical control in an adjustment to
establish GPS derived orthometric heights (± 2cm) on all the CGPS stations in Southern
California (the 10 southernmost counties). This process is to help fulfill the CSRC’s
function of providing vertical spatial reference to surveyors and other geodetic users in the
State of California. This section will detail the differential leveling process used to establish
these elevations.
The CSRC was formed to provide a better source of geodetic, spatial reference to surveyors,
engineers and other users in the State of California (CSRC, 2002). The CSRC helps users
take full advantage of the SCIGN network (Hudnut, et al, 2001) of over 250 CGPS stations
in Southern California. These stations have been rapidly adopted for use by surveyors and
other users for the horizontal control of projects. Since the geodetic positions of these CGPS
stations are calculated daily and immediately updated after a seismic event by
SCIGN/SOPAC, the user community has a free, highly accurate and well maintained spatial
reference system in a state plagued by crustal motion, seismicity and subsidence. Utilities
available to CSRC users (e.g. SECTOR (CSRC, 2004); HTDP (Snay, 2003; 1999)) allow
them to take into account the updated positions yet continue to work in a past epoch if
necessary for their particular project.
The vertical spatial component has not been as easy to maintain. Although Southern
California has hundreds of miles of differentially leveled first order NAVD88 benchmarks,
there is no easy way to maintain or otherwise update the elevations after a seismic event.
The immense cost of leveling these benchmarks can no longer be funded by the National
Geodetic Survey (NGS), the Metropolitan Water District (MWD) and the local counties and
agencies that were largely responsible for the initial leveling networks. The CSRC realized a
need to establish orthometric heights on the CGPS stations to provide a maintainable vertical
spatial reference for the geodetic users in California. The first step in this process was to
establish a differential elevation on a group of CGPS stations that would then be the vertical
control for the orthometric height adjustment (Zilkoski et al, 1997; Zilkoski et al, 2003).
This section will detail the methods we utilized to establish these elevations on the BPA and
GRM at the CGPS stations.
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Preliminary Project Planning (before issuance of contract)
Selection of CGPS Stations
This project was to cover the ten southern counties of California – from the 36th parallel
down (San Luis Obispo, Kern, San Bernardino, Santa Barbara, Ventura, Los Angeles,
Orange, Riverside, San Diego and Imperial Counties). The first step of this project was to
select a group of stations that would provide a good geometry over these counties in the
final adjustment. With a finite budget in mind, we had to determine the number of
stations to level to, the specification to use, the equipment to use, the proximity of the
station to existing NAVD88 first order benchmarks, the vertical stability of the station
(proximity to seismic or subsidence areas, etc.) and the type of CGPS monument.
The CSRC works in conjunction with the NGS and it was important that upon completion
these elevations would be accepted into the national database, so we decided to complete
the leveling at the Second Order, Class II criteria of the FGCS Specification and
Procedures for Electronic Digital/Bar Code Leveling Systems (FGCS, 1994). This
specification would be accepted by NGS and would also provide an elevation ≤ 5mm
accuracy. This accuracy for our vertical control would allow the CSRC to achieve the end
goal of orthometric heights at ± 2cm accuracy as stated in the CSRC Master Plan for the
Geodetic Control (CSRC, 2003).
One mandate of the CSRC is to provide contracting opportunities for the private sector
since we receive funding from the federal government. This leveling project was to be
contracted out so when deciding what equipment to use, it was decided to use the newer
electronic digital leveling equipment since it is commonly in use by the private sector and
would provide a broader opportunity for respondents. Both of these first two decisions
had details that later had to be worked out with NGS and will be detailed below.
A major determining factor in selecting the stations to level was proximity to existing
NAVD88 first order benchmarks. Searches of the NGS database were done to determine
the number of first-order adjusted benchmarks within a two mile radius of the station.
Stations were selected that had at least 4 or more benchmarks within the two mile radius,
knowing that in some cases the elevations would have changed over the years and that
leveling would have to be extended to check into additional benchmark(s) to meet the
specifications.
Along with proximity of the benchmarks, site accessibility/condition and elevation
difference were also reviewed. Several sites were originally accepted based on proximity
of benchmarks and network geometry, but later had to be rejected based on the severe
elevation difference, and therefore, expense, to level to the site. Another seemingly
suitable site was rejected due to frequent vandalism, which put into question the longterm viability of the site as part of the network. Stations were also reviewed for known
subsidence issues in their area and one station was rejected based on that issue.
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CRBT
CCCC
BKAP
LVMS
VNPS
VNDP
VTIS
MVFD
GLRS
NAVD88 Elevations/Levels per this contract
Possible alternative sites
NAVD88 Elevations completed
Figure No. 1. Map showing CGPS Stations included in leveling contract.
It was decided that each station was to be the Wyatt drilled-braced monument with choke
ring antenna with radome that were installed by the SCIGN group (SCIGN web site).
These stations have been shown to have the best stability, with the least measurement
noise (Williams et al, 2004). Stations installed in the earlier years of the SCIGN project
had less rigorously designed monuments and were used in only a few cases where there
was not a more suitable monument available (VTIS, VNDP and VNPS). Each station’s
vertical time series was reviewed to select those stations that had the lowest RMS values.
Stations with RMS ≤ 5mm in the vertical were selected.
Geometry of the network was a major consideration, so after stations were evaluated on
all the above criteria, they were chosen to provide 80 km spacing over the 10 counties (or
as close to that as possible) with the qualified stations. After evaluating these issues and
the estimated cost on a station by station basis, the following 20 stations were chosen and
are shown in Figure No. 1.
1.
2.
3.
4.
CRBT – Camp Roberts, Monterey County
USLO – Cal Poly State University, San Luis Obispo County
VNDP – Vandenberg Air Force Base, Santa Barbara County
COPR – Coal Point Oil Reserve, Santa Barbara County
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5. BVPP - Buena Vista Pumping Plant, Kern County
6. RSTP – Rosamond Treatment Plant, Kern County
7. CCCC - Cerro Coso Community College, Kern County
8. LVMS – Lockwood Valley Maintenance Station, Ventura County
9. TOST – Thousand Oaks Sheriff Station, Ventura County
10. VNPS – Vincent Pump Station, Los Angeles County
11. VNCX – Van Norman Complex, Los Angeles County
12. ELSC – East Los Angeles Science Center, Los Angeles County
13. VTIS – Marine Exchange, Los Angeles County
14. BSRY – Barstow Road Yard, San Bernardino County
15. BKAP – Baker Airport, San Bernardino County
16. NDAP – Needles Airport, San Bernardino County
17. MVFD – Montezuma Valley Fire Department, San Diego County
18. NSSS – Naval Space Surveillance Station, San Diego County
19. GLRS – Galeano Reservoir, Imperial County
20. IID2 – Imperial Irrigation District, Drop 2, Imperial County
Selection of Leveling Specifications
As stated above, we needed to achieve final elevations that would be accurate enough to
use as vertical control in the orthometric height adjustment to provide final GPS derived
orthometric heights at the ±2 cm level. We had to evaluate several factors to determine
what specification to follow. While we would have liked to achieve the vertical accuracy
provided by First Order leveling, we had to consider the high cost of this type of leveling
and the fact that few consultants would have the expertise or equipment to perform this
type leveling, and would therefore limit the response to our contract. Another limitation
we had to consider was the allotted budget amount for this project. We decided to use the
FGCS specification for Second Order, Class II leveling to provide final positional
accuracies of our elevations in the 5mm range at 95% confidence level and to allow for
the most number of stations to be leveled to with the amount of funding available. We felt
this specification would also open the contract up to more consultants since the
equipment needed would be more commonly in use than that required for First Order
leveling.
Modifications to FGCS specifications
The CSRC did a review of the FCGS specifications (1994) in an effort to clarify the
methods to be used to level to CGPS stations. In an effort to be as efficient as possible,
and to get the most from a limited budget, we worked with NGS to create a modified
specification to use for this leveling project. We started with the FGCS Second Order,
Class II specification and made the following modifications with NGS approval.
1. We would perform a single run benchmark check between two NGS published,
First Order benchmarks that had to agree with the specifications definition of a
valid check connection (in our case, 8mm times the square root of the shortest one
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way distance). If we didn’t meet this valid check connection, we would run to
another benchmark until we had a valid benchmark check connection. Checking
into one benchmark at each end of the leveling run was a change from the FGCS
specification that calls for two at each end.
2. The level run to the CGPS had to be double run, either from one benchmark and
back or from one benchmark to the CGPS station and then to the other benchmark.
3. We had to keep the length of the leveling line from each valid benchmark to the
CGPS at 10 km or less.
4. We were not going to set any interim benchmarks, but had to use stable pins or
turning pucks for all turns and/or temporary benchmarks.
These modifications and other suggestions and clarification for field work for this project
were written up in a document titled CSRC Specifications and Procedures for Second
Order, Class II Geodetic Leveling to Establish Elevations on CORS (dated March 10,
2003) and was included as part of the contract documents. It has also been posted on the
CSRC web site for other users. It is included as Appendix A to this paper.
Determining Methods to Measure to GRM, BPA and ARD
When designing this leveling project, discussions were held to determine the best method
for measuring to the geodetic reference mark (GRM) and the base of the pre-amp (BPA)
of the antenna, with the least amount of disruption of the data/GPS signal. The original
idea was to remove the radome, the antenna and the top half of the SCIGN adaptor
(SCIGN, 1999 a) to level directly on the GRM. It was decided that this method would
cause too much disruption of the
equipment and GPS signal. An alternative
method was derived that would give us the
measurements needed to calculate all
elevations required.
Each CGPS has a reference mark or divot
(ARD) on one of the tripod legs. This
mark was created as part of the original
installation contract of the Wyatt drilledbraced monument installations (CSRC,
2003). (A similar mark was created on the
other types of monument installations for
use in this leveling project.) The leveling
project would establish an elevation on
each of these ARD using the electronic
leveling equipment. From this ARD mark,
a manual measurement (using a steel rule)
would be made up to the bottom of the
Figure No. 2. Typical SCIGN antenna.
antenna adaptor, which can be accessed
from the underside of the tripod/antenna
connection. Then the radome would be removed which allows access to measure from the
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bottom of the adaptor to the top of the adaptor. This measurement was to be done in each
of the cardinal directions, in both meters and feet (for a check), and then averaged to
determine the adaptor height. These measurements allow for calculation of the GRM and
BPA elevations, based on the machining specifications of the adaptors (SCIGN, 1999),
and are able to be completed in a few minutes for minimized disruption of the GPS data.
The following general formulas are used to determine the elevations:
Leveled ARD elevation + distance to bottom adaptor + adaptor height = BPA elevation
BPA calculated elevation – 0.0083 meters = GRM elevation (with SCIGN adaptor)
The time of removal and replacement of the radome was to be recorded for use by
SOPAC/SCIGN to track any anomalies in the data.
Field Project Mobilization (after issuance of contract)
Once the final sites were determined, site contact personnel were notified of the pending
survey. This proved to be more of an issue than initially expected due to the fact that
many of the on-site contacts listed in the SCIGN database had retired or moved on since
last contacted by any of the CGPS network personnel.
Field note forms to be used in the reconnaissance phase were prepared. Two different
forms were prepared. The first form was designed for use in recording the site condition
and the measurements necessary to determine the height difference from the antenna
reference divot (ARD), which is generally a punch mark on the leg of the CGPS tripod.
Additionally, this form was used to record the surveyor, date, the time of removal and
reinstallation of the radome, the antenna make and the antenna serial number (see
Appendix B for example).
The second reconnaissance form was designed to record the condition of the found
benchmark monuments (see Appendix C for example). These note sheets had blanks for
recording the NGS permanent identification numbers (PID) of the marks and the
stampings of the marks. The form provided blanks for latitude and longitude of the mark
as determined by handheld GPS, suitability for use of the mark by GPS, and space for
any notes thought necessary by the field surveyor to show changes from the NGS records,
or any other data that might be pertinent to the project. Additionally, space was provided
for the field surveyor to note his idea of the most logical route of leveling from the
nearest located bench mark to the subject CGPS station. A location on the form was also
provided to note the date that the field data was transmitted to the NGS via the NGS
Online Recovery Program.
A digital map file was prepared for each site showing the CGPS location as well as the
NGS record location of the nearest five bench marks (see Appendix D for example). This
allowed our field surveyors to drive directly to the area and to the best available record
location of the bench marks using GPS navigation and moving map technology. In
addition to the map, NGS data sheets were obtained via the NGS website for all of the
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known bench marks near the CGPS sites. These were furnished to the field surveyors in
both printed and digital format for their use in locating, identifying, and verifying the
existence and usability of the vertical control in the area.
All necessary changes to the NGS records, along with the handheld GPS positions, which
were derived from the reconnaissance operation, were transmitted to the NGS for
incorporation into the National Geodetic Survey database via the NGS Online Recovery
System.
Field Leveling
The following is the initial leveling instructions and procedures to field crews:
Main Idea for Field Leveling:
At each CGPS site, level from the nearest NGS 1st order NAVD88 benchmark to the
antenna reference divot (ARD) (“punch mark”) on the CGPS “tripod” leg or base,
following the Second Order, Class II CSRC Modified Specification (Appendix A). This
specification details the process of a double run (closed loop) from the benchmark to the
CGPS site with an additional single run to a second 1st order benchmark for a check.
Recommended Equipment:
Leica NA 3003 Digital Level (with Version 3.3 firmware or higher) or equivalent
Certified one piece bar code rods, with the stays (recommended)
Stiff leg tripod
Turning pucks
Turning drive pins
Steel rule, calibrated in meters and feet
Field Procedures:
1. Calibration (collimation of level) to be accomplished once per day and the result
entered into the level and used until the next calibration.
2. When using turning pucks for turn point, make sure personnel handling the rod are
trained to step on the puck to assure that it is down as far as it will go and completely
stable during the turn. Also make sure any drive pins set for turns are completely
stable.
3. Maximum site length not to exceed 60 meters (Leica level specification)
4. Backsight/Foresight balance to be not more than 10 meters per setup and 10 meters
accumulated per section.
5. Designate one rod as “A” Rod, use an even number of turns per section to make sure
you take off the bench with “A” Rod and get back on the next bench with the same
“A” Rod.
6. Maximum difference between forward and backward running of the double run lines
not to exceed 8mm times the square root of the shortest one way length of section in
kilometers.
7. Maximum difference between record elevation difference and single run difference to
verification bench to also be less than 8mm times the square root of the shortest one
way length of section in kilometers. If first run between benches does not pass, run
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back to the initial bench. If your two runs match each other to the above spec but still
do not match the record, you must run to further benches.
8. If any runs/sections are more than 3 kilometers, set a drive pin as a temporary bench
to make sections 3 km or less in length, in order to isolate any errors and minimize
the amount of reruns necessary to correct any errors.
9. The last turn into the ARD will have to be made with the “A” Rod on the turning
puck and the stainless steel 6” ruler read with the optical cross hair and hand entered
into the gun. Make this a short turn with about a 5-10 meter sight distance (far enough
away to focus, but as close as possible to negate any inaccuracies in the optical
reading) (see Figure No. 3).Turning back out from the ARD would be just the
opposite of the above.
10. For verification of the benchmark elevations in the field, it is a good idea to have
previously run the planned benchmarks through the NGS program LVL_DH (Shields,
2003), to determine the elevation difference that takes the gravity correction out of the
published difference to give a difference that should match raw leveling. This is the
difference that we are trying to match.
11. Review guidelines for NGS project submittals regarding field raw data file. There are
specific guidelines for recording the temperatures at the beginning and end of a section,
the instrument person, the time of leveling, etc. Also the curvature function should be
turned off in the level and the data should be collected in meters. Appendix A has some
of this information, with additional references to help determine the correct field data
file collection methods.
12. A unique identifier should be assigned to each mark to be elevated. The last four
numbers of the NGS PID could possibly be utilized for the BM’s. Other marks should
be identified so to avoid identical numbers in other sections of the leveling project.
Figure No. 3. Last turn into ARD is read optically from level (left) to steel rule held at ARD
(right) and manually entered into level for recordation in raw data digital file.
Radome removal and BPA measurement training
1. At each CGPS, measure two vertical distances – a) from the reference mark on the
CGPS leg to the bottom of the CGPS antenna adaptor and b) from the bottom of the
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2.
3.
4.
5.
adaptor to the top of the adaptor – all in accordance with CSRC procedures. The
vertical distance from the bottom to the top of the adaptor shall be the average of four
measurements at different locations, approximately 90 degrees apart, around the
adaptor. All measurements shall be made to the nearest millimeter and shall be
accurate to plus or minus one millimeter.
Each measurement shall be verified by re-measuring with a measuring device
graduated in feet. Only measurements that have agreement between the metric and
foot measurements of one millimeter or less shall be accepted.
The field notes shall show and document all GRM measurements. To make the GRM
measurements, it is necessary to remove the CGPS radome to provide access to the
CGPS antenna adaptor.
Under no circumstances remove, adjust, or manipulate the CGPS antenna.
Use care in the removal and reinstallation of the CGPS radomes. Prior to removing
each radome, note and mark the position of the radome. When the GRM
measurements for each CGPS are completed, immediately reinstall the radome in the
exact position as originally installed (for instructions, see SCIGN, 1999 b & c).
Figure No. 4. Manual measurement from ARD to bottom of antenna adaptor (left) and
from bottom of antenna adaptor to BPA (right).
Equipment Used
For the differential level measurements necessary for this project the following
equipment was used:



Leica NA3003 Digital Level, SN 91716 with recent service record
Leica Invar Geodetic 3 Meter Leveling Staff GPCL3, SN 22962 with calibration
certificate
Leica Invar Geodetic 3 Meter Leveling Staff GPCL3, SN 23219 with calibration
certificate
In addition to the above major equipment, both rods were equipped with stays, to hold the
rod plumb and stable while being read, and dual level bubbles to assure that neither
bubble had become out of level during the survey. Kern leveling turtles (pucks) were
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utilized for solid, stable, but portable, turning points. The same equipment was used
during the entire project (see Figure No. 5 for example).
Specification and Equipment Issues during Initial Field Work and Office Processing
Once field leveling started,
we realized we apparently
weren’t meeting the
specification criteria of
0.1mm standard deviation for
each measurement. To
achieve a value of 0.1mm for
a measurement, we had to
use sight lengths of 25 – 30m,
even though the FGCS
specifications allow a much
longer sight length for
Second Order, Class II. It
was unclear in the FGCS
specifications if this was to
be 0.1mm standard
deviation of “a reading”
Figure No. 5. Leveling equipment used – Leica
(=± (r2/(n-1))) or of the
NA3003, Invar staffs with stays, stiff leg tripod.
“mean of three readings”
(standard deviation of the mean = m=±/n). It was also unclear at first what was being
recorded in the Leica digital leveling file. We called both NGS and Leica to get
verification of what we were trying to achieve and what we were achieving, respectively.
We got a final determination from the NGS that this specification is supposed to be the
standard deviation of the mean even though the FGCS document (1994 version) is not
clear on this. From Leica we got clarification that when running in the mean mode on
their Version 3.3 firmware, the standard deviation being reported in the raw data file was
the standard deviation of the last single reading and not the standard deviation of the
mean of the number of readings taken. They also gave us guidance on how to use their
“Mean Mode with Entered Std Dev” to assure that we were meeting the 0.1 mm
specification for the mean of three measurements. This information from Leica meant
that an update to the digital level firmware was needed since we were using an older
version (Version 3.2) that didn’t have this functionality. After the upgrade, we set the
level to record in the “Mean Mode with Entered Std Dev”, which allows the level to
record only when it attains an acceptable standard deviation of the mean. The level
firmware allows for entering of a standard deviation for 20 m sight length. Internally, the
level computes the standard deviation for the length of sight being taken by use of a
straight-line proportion, i.e., if set to 0.03mm@20m the level will accept 0.09mm@60m.
Since the level will not physically read a sight length longer than 60 meters, it will never
accept a set of readings that are outside of 0.09mm standard deviation. Using this mode,
we were able to complete the second half of the project using 50± meter sight lengths and
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still obtain the same closure accuracies that we attained in the first half of the project
using 25 meter sight lengths, and in a much more efficient manner.
The criteria stating a 0.1mm standard deviation for three measurements was the most
problematic specification to meet in the field and the following are the
changes/improvements to our field procedure that we made to meet this specification
(after updating to the version of Leica firmware with the necessary capabilities).
1. Set your level to run in the mean mode with the standard deviation set to 0.03mm for 20
meters and keep your sight distances in the 40 to 60 meter range.
2. Watch the standard deviation as field measurements are taken to verify that it is
improving with additional measurements and that it meets the specification of 0.1 mm
standard deviation of the mean when recorded. (In the office, you will not be able to
verify this by looking at the 52 record in the raw file for each foresight measurement
accepted. For example, in the Leica raw file “52..0003+010” means 3
measurements were taken in the field and the last one resulted in a standard deviation
of 0.1mm. The standard deviation of a single measurement is reported in the data file,
no matter which mode you are using to run the level.) Refer to your level manual for
the details of the values recorded and the code explanations.
3. Alternatively, set your tolerance for 0.04mm for 20 meters and keep your sighting
distances less than or at 50 meters. Set this way, the instrument will not record a
measurement that would exceed the specification of 0.1mm standard deviation of the
mean.
4. Try to perform leveling in temperatures less than 90 degrees.
5. Keep instrument shaded during measurements.
6. Verify that rod is absolutely stable when measurements are being taken.
7. If not meeting the standard deviation on a particular shot, try the measurement with a
shorter sight distance to see if standard deviation improves (which would indicate an
atmospheric condition between rod and instrument). If it doesn’t improve, problem is
probably at instrument so you will need to check for settling of instrument, vibrations
of instrument (from road, wind, etc), or if the instrument is not shaded and possibly
too hot. Failure to achieve the standard deviation specification of a particular set of
measurements is an indication that the level is not able to resolve the measurement
precisely.
Rod stays were not initially required, but by experience, made meeting this specification
much easier by eliminating rod movement (allowed for meeting measurement standard
deviation at somewhat longer sighting distances than would otherwise be possible). By
experience, the sight distance is usually in the 35 to 50 meter range to meet all the required
specifications (especially the standard deviation of the measurements). Additionally it
should be noted for future surveys, that the firmware for the digital level to be utilized, must
be studied to verify that the algorithm being used and stored in the level, meets the
specification criteria. (The FGCS specifications (FGCS, 2004) have been updated to reflect
the standard deviation of the mean clarification.)
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Field verification of level run closure/specifications met
Table No. 1
CGPS FROM
Sample Benchmark Elevation Checks/Verification
TO
LVL_DH MAX
Double
DIST NAVD88 Corrected Allowed Single Run
Run
HT DIFF (m) (km)
Diff
Diff Misclosure Misclosure Misclosure
BKAP FT1138 FT0056
-2.4992
1479
-2.501
-2.501
0.010
0.002
BSRY EV0028 EV0027
-2.9437
206
-2.940
-2.939
0.004
-0.005
EV0027 EV0028
2.9434
206
2.940
2.939
0.004
0.004
EV0027 EV0044
5.8967
1139
5.895
5.897
0.009
0.000
BVPP FU2195 FU2197
-1.9412
85
-1.935
-1.935
0.002
-0.006
FU2197 FU2195
1.9403
85
1.935
1.935
0.002
0.005
FU2195 FU3245
25.7484
1305
25.771
25.771
0.009
-0.023
FU3245 FU2195
-25.7493
1303
-25.771
-25.771
0.009
0.022
FU2191 FU3245
-22.2549
906
-22.259
-22.259
0.008
0.004
CCCC FT0640 FT0638
-16.8391
1566
-16.842
-16.837
0.010
-0.002
COPR EW3794 EW3793
-17.9157
1393
-17.920
-17.920
0.009
0.004
EW3793 AE4854
-2.6773
981
-37.348
N/A
0.008
34.671
AE4854 EW3793
2.6766
978
37.348
N/A
0.008
-34.671
CRBT FV0260 FV0203
-9.0498
1614
-9.048
-9.048
0.010
-0.002
-0.0003
-0.0008
-0.0009
-0.0007
At each of the 20 CGPS sites, we leveled from the nearest existing bench mark to the 2nd
nearest existing bench mark using the above mentioned FGCS Second Order, Class II
Specifications (2004; NGS revised version 4.1; now using std. dev of the mean) and
CSRC specifications (Appendix A). The field-derived difference in elevation was
compared to the published difference in elevation after removing the orthometric
corrections using the NGS program LVL_DH. If the run between the benchmarks
matched the published difference within the specification tolerance of 8 mm times the
square root of the shortest one-way leveled distance between the two benchmarks, the
benchmarks were considered validated.
If the field leveled, single run difference did not match, the crew leveled back from bench
2 to bench 1 to verify the loop misclosure of the field leveling. If the verification run
matched the single run (which they did in all cases), then we continued to level to more
distant existing bench marks until such time as we found two existing bench marks
between which our field leveling matched the record difference within the stated
tolerance (see Table No. 1 for example).
Once, we had two “validated” benchmarks, we ran from the nearest validated bench to
the CGPS, along the nearest and flattest route available. As per the CSRC specifications
(Appendix A), we used drive pins as temporary bench marks along any route that was
more than 3 km to the CGPS to break the run into “sections” of less than 3 km. At the
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CGPS, we used a small stainless steel ruler graduated in millimeters (Westcott 10414) as
the last rod shot to the ARD point on the CGPS tripod leg. After turning into the CGPS,
we ran back from the CGPS to the starting bench along the same route, using the same
specs, and across the same temporary benchmarks. The forward run was compared to the
return run to assure that we again matched the specified tolerance of 8 mm times the
square root of the kilometers. In all cases our results matched well within the allowable
tolerance (see Table No. 2 for example).
Table No. 2.
CGPS
SITE
BKAP
BSRY
BVPP
CCCC
COPR
CRBT
Double Run Closures from Validated Benchmarks to CGPS ARD.
FROM
TO
Height
Difference
(m)
Single Run
Distance
(m)
Double
Run
Closure
Maximum
Allowable
Closure
FT1138
BKAP ARD
BKAP ARD
FT1138
-1.31269
1.31135
1137
1134
-0.001
0.009
EV0044
BSRY ARD
BSRY ARD
EV0044
-2.45185
2.45104
1193
1193
-0.001
0.009
FU2197
BVPP ARD
BVPP ARD
FU2197
-69.28625
69.29930
8698
8695
0.013
0.024
FT0638
CCCC ARD
CCCC ARD
FT0638
-82.62379
82.62162
3661
3656
-0.002
0.015
EW3793
COPR ARD
COPR ARD
EW3793
-15.02212
15.02446
3793
3790
0.002
0.016
EV0260
CRBT ARD
CRBT ARD
EV0260
53.40328
-53.40316
1310
1309
0.000
0.009
Office Procedures
As the field leveling was completed to each site, the raw data file was downloaded from
the level using the proprietary download software. The raw field data was reviewed for
quality control and processed to perform a preliminary adjustment of the data. After the
preliminary analysis and quality control was complete, preparation of files for submittal
to NGS for publication of the elevations were completed.
Several programs were used for the handling of the leveling data. In addition to the
proprietary download program (that usually comes with the purchase of the level), a
program called StarNetPro was used to process the raw data file and adjust the extracted
elevation differences. A program called NABOOK was used to create a field book file
that was used to find errors and data that did not meet specifications. (Be aware that the
program may incorrectly flag standard deviation, as standard deviation of the mean.) This
program also is used to create some of the files needed for the NGS publication process.
The following is a simplified outline of the usual procedure, but the process is described
in detail in Appendix E:
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Initial data processing and quality control:
1. Download digital raw data file from level using proprietary software.
2. Review the ASCII raw data file for input errors and needed revisions.
3. Using a utility called NA3000, extract the elevation differences and distances for
adjustment in StarNetPro.
4. Using StarNetPro, run a preliminary adjustment of the data for quality control.
5. Once quality control has been completed on raw data file, it is ready for NGS
submittal preparation.
Preparation of files required for NGS data submittal process is a complex process and
requires familiarity with several documents and programs. For detailed instructions of
the submittal process, refer to the documentation Murray (1999), NGS (1992) and the
NGS web site. We have detailed the process we followed (in conjunction with these
other documents) in Appendix E.
Summary
At two locations, we had problems validating benchmarks. Those locations were at the
Buena Vista Pumping Plant station (BVPP; 158 meters) and at the Rosamond Treatment
Plant station (RSTP; 745 meters). Unknown to us prior to the project, both of these
stations are near the edges of known subsidence areas. At the BVPP site, we had to level
to four existing benchmarks, instead of the normal two, before we found two that would
agree with the record differences within Second Order, Class II tolerances. At the
Rosamond Site, we leveled to five benchmarks before finding two that would agree
within the project tolerances.
The resulting elevation determined at the geodetic reference mark (GRM) by leveling at
BVPP is 20 cm higher than the height for that same mark determined from the CSRC
published ellipsoid height, minus the geoid height determined from NGS’ current geoid
model (Geoid 03), which could be explained by equally subsiding benchmarks. However, at
RSTP, where we actually had more trouble validating benchmarks, the same difference is
only 4cm, which is not that much different than many of the other sites within the project.
At the Montezuma Valley Fire Department CGPS station (MVFD) in San Diego County,
we had no trouble validating benchmarks, but the difference between the leveled GRM
height and the same height determined from the ellipsoid height and Geoid 03 missmatches by 11 cm. This site is located in Montezuma Valley at 1220 meters elevation in
San Diego Co. (The only NAVD88 benchmarks in this area were third-order.)
We find a similar situation at Galeano Reservoir CGPS (GLRS) near the Salton Sea in
Imperial County, where the benchmarks fit each other, but the result misses by 12cm.
This region is known for subsidence, so all of the benchmarks may have experienced the
same magnitude of subsidence.
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Acknowledgements
The authors would like to acknowledge the assistance of Dave Zilkowski, Dale Pursell and
others at NGS who worked with the CSRC to modify and clarify the FGCS specifications
for this type of leveling. We also appreciate the assistance of Orland Murray, Charles
Whalen and Kathy Koepsell with the NGS “blue booking” process. Special thanks go to the
leveling crews from Johnson-Frank & Associates and Riverside County Flood Control
District for their patience, perseverance and assistance with implementing and troubleshooting these procedures and assuring that the project specifications were met.
References
California Spatial Reference Center (CSRC) (2004). “Scripps Epoch Coordinate Tool and
Online Resource (SECTOR)”. R. Nikolaides, “Observation of Geodetic and Seismic
Deformation with the Global Positioning System, Ph.D. thesis, University of California,
San Diego”, 2002. http://sopac.ucsd.edu/processing/refinedCoordsDoc.html
California Spatial Reference Center (CSRC) (2003). SCIGN GPS Site Monument
Information. http://csrc.ucsd.edu/howTo/SCIGNMonumentInfo.html
California Spatial Reference Center (CSRC) (2002). “A Master Plan for a Modern
California Geodetic Control Network – A Plan to Implement the National Height
Modernization Program Goals in California”. Scripps Institute of Oceanography,
University of California, San Diego, October 18, 2002.
http://csrc.ucsd.edu/input/csrc/csrcMasterPlan.pdf
Federal Geodetic Control Subcommittee (FGCS) (5/27/2004). “FGCS Specifications and
Procedures to Incorporate Electronic Digital/Bar-Code Leveling Systems, Version 4.1”.
http://www.ngs.noaa.gov/FGCS/tech_pub/Fgcsvert.v41.specs.pdf
Federal Geodetic Control Subcommittee (FGCS) (6/14/1994). “FGCS Specifications and
Procedures to Incorporate Electronic Digital/Bar-Code Leveling Systems, Version 4.0”.
http://www.ngs.noaa.gov/FGCS/tech_pub/Fgcsvert.v40.specs.pdf
Leica Geosystems (1996). NA2002/NA3003 Version 3.2/3.3 Instrument Manual.
Hudnut, Kenneth W., Yehuda Bock, John E. Galetzka, Frank H. Webb, and William H.
Young (2001). "The Southern California Integrated GPS Network (SCIGN)."
Proceedings of Commission 6, of the International Federation of Surveyors, Deformation
Working Group, 10th International Symposium on Deformation Measurements, Orange,
California, USA, pp. 129 to 148.
Murray, Orland W. (1999). “Digital Leveling User’s Guide – Using the Leica NA Series
of Digital Levels in Accordance with FGCS Specifications and the Input Formats and
Specifications of the National Geodetic Survey Data Base”. (NOAA Document)
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National Geodetic Survey (NGS) (1992). “Vertical Control Field Data Processing System,
Version 3.00”. National Oceanic and Atmospheric Administration, Charting and
Geodetic Services, National Geodetic Survey Division.
SCIGN (1999). Antenna adaptor design and specification drawings.
a.) http://pasadena.wr.usgs.gov/scign/group/dome/adaptor.html
b.) http://pasadena.wr.usgs.gov/scign/group/dome/instr_short.html
c.) http://pasadena.wr.usgs.gov/scign/group/dome/instr_tall.html
Shields, Rene (2003). “LVL_DH and Tidal and Orthometric Elevations”. Professional
Surveyor, July 2003, page 31. http://www.ngs.noaa.gov/TOOLS/LVLDH/lvldh.shtml
Snay, Richard (2003). “Horizontal Time Dependent Positioning”. Professional Surveyor,
November 2003, pages 30 -34.
Snay, Richard (1999). “Using the HTDP Software to Transform Spatial Coordinates
Across Time and Between Reference Frames”. Surveying and Land Information Systems,
Vol. 59, No. 1, 1999, pages 15-25. http://www.ngs.noaa.gov/CORS/utilities3/
Williams, S.D.P., Y. Bock, P. Fang, P. Jamason, R.M. Nikolaidis, L. Prawirodirdjo, M.
Miller, D.J. Johnson (2004). “Error Analysis of Continuous GPS Position Time Series”.
Journal of Geophysical Research, 109 (B03412), doi: 10.1029/2003JB0022741, 2004.
Zilkoski, David B., Edward E. Carlson and Curtis L. Smith (2003). “Guidelines for
Establishing GPS Derived Orthometric Heights, 2 cm and 5 cm Standards, Draft Version
1.4”. NOAA Technical Memorandum, NOS NGS-59, Silver Springs, Maryland, USA.
Zilkoski, David B., Joseph D. D’Onofrio and Stephen J. Frakes (Nov 1997). “Guidelines
for Establishing GPS Derived Ellipsoid Heights, 2 cm and 5 cm Standards, Version 4.3”.
NOAA Technical Memorandum, NOS NGS-58, Silver Springs, Maryland, USA.
http://www.ngs.noaa.gov/PUBS_LIB/NGS-58.html
Web Site References
NGS Web Site: http://www.ngs.noaa.gov/
SCIGN Web Site: http://www.scign.org/
SOPAC Web Site: http://sopac.ucsd.edu/
CSRC Web Site: http://csrc.ucsd.edu
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Appendix A – CSRC Specifications and Procedures document (as originally issued)
Specifications and Procedures for Second Order, Class II
Geodetic Leveling to Establish Elevations on CORS
(within 10 km of valid vertical control and using digital/electronic bar-code leveling
systems)
March 10, 2003
1. Description: These specifications and procedures specify the requirements for
performing second order, class II geodetic leveling, using electronic digital/bar-code
leveling systems, to establish elevations on continuously operating reference stations
(CORS). The application of these specifications and procedures is limited to
establishing elevations on CORS that are within 10 km of a valid vertical control
station.
2. Requirements: The leveling work shall conform to the second order, class II
specifications and procedures specified in the Federal Geodetic Control
Subcommittee (FGCS) document entitled “FGCS Specifications and Procedures to
Incorporate Electronic Digital/Bar-Code Leveling Systems,” adopted June 14, 1995,
and the requirements specified in this document. The referenced FGCS document is
referred to as the “FGCS Specifications” hereafter. This document is available from
the National Geodetic Survey (NGS) website at
“http://www.ngs.noaa.gov/FGCS/tech_pub/FGCSvert.v40.specs.pdf.” The FGCS
Specifications shall apply unless specifically superseded by the requirements
specified below. If there is a conflict between the FGCS Specifications and this
document for a given specification or procedure, this document shall take priority.
3. Network Geometry:
a. Bench Marks – Bench marks are not required to be set. However, temporary
bench marks that are suitable for the purpose intended shall be set in accordance
with the spacing specified for bench marks in the FGCS Specifications. The
temporary bench marks divide the leveling line into sections for these
specifications and procedures.
b. Bench Mark Ties – The minimum bench mark tie shall be one valid bench mark
(vertical control station) conforming to the specifications below.
c. Valid Bench Mark – A valid bench mark shall conform to the following:
i. Each valid bench mark shall have a NGS-published, second-order, class II (or
better) adjusted NAVD88 elevation value. Priority shall be given to those
bench marks that are included in the California High Precision Geodetic
Network.
ii. Each valid bench mark shall have an acceptable “check connection” with an
adjacent second-order, class II (or better) bench mark having an adjusted
published NAVD88 elevation value. The check connection shall be run either
a) from the valid bench mark directly to an adjacent bench mark or b) from the
CORS to a bench mark adjacent to the valid bench mark. The allowable
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tolerance limit for a check connection shall be 8 mm times the square root of
the shortest one-way distance of the check connection, in kilometers, (8√L).
Note: The FGCS Specifications permit check connections to be single run.
iii. The length of the leveling line from each valid bench mark to the applicable
CORS shall be 10 km or less.
d. Connections to Other Network Control Points – Other than specified above,
connections to other network control points are not required.
4. Instrumentation:
a. Leveling System – An electronic digital/bar-code leveling system shall be
used for all leveling work. The leveling system shall be in good condition
and shall have been serviced, by an authorized service center, within the
last six months.
b. Instrument Tripod – The instrument tripod shall have non-adjustable legs
(fixed-length legs).
c. Temporary Bench Marks – Temporary bench marks shall be driven steel,
turning pins similar to the turning pins utilized by NGS or an acceptable
equivalent. A suitable driving cap shall be utilized when driving the pins.
d. Turning Points – The use of steel turning pins and turtles is not required
for turning points but is recommended. Turning points shall be stable
points and suitable for the leveling work being performed.
e. Bipods – The use of bipods to provide stable rod plumbing is
recommended but not required.
f. Umbrella – The use of an umbrella to shade the leveling instrument is not
required unless recommended by the instrument manufacturer. In other
cases, the use of an umbrella to shade the instrument from a bright sun is
recommended.
5. Calibration Procedures:
a. Collimation Time Interval – The time interval between collimation error
determinations shall not be longer than one day for all leveling instruments.
This information shall be recorded as part of the leveling raw dataset.
6. Field Procedures:
a. Minimal Observation Method – The “electronic digital/bar-code” leveling
method shall be used for all leveling work.
b. Section Running – The “double run” leveling procedure shall be used to
perform the leveling from the valid bench mark to the CORS.
7. Office Procedures: The paragraph in the FGCS Specifications, under Office
Procedures, regarding normalized residuals and least squares adjustments models
does not apply to this leveling work, except the superscript footnote “n” for
collimation error shall apply.
(end)
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Appendix B – CSRC Antenna Measurement Form
Example of completed form for a CGPS site.
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Appendix C – CSRC Benchmark Reconnaissance Form
Example of completed form for the benchmarks for the level runs to a CGPS site.
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Appendix D – CSRC Site Leveling Plan
Example of leveling plan for a CGPS site.
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Appendix E - Data Processing For NGS Vertical Project Submission
Once the raw leveling data file is collected from the field, it needs to be properly
formatted and processed for submission to be included in the NGS database (a process
that is commonly called “blue booking”). The guidelines in the next sections will step
through this process, which utilizes three NGS program suites, NABOOK, VFPROC, and
WDDPROC. (The NABOOK program has to be purchased by the user; the VFPROC and
WDDPROC programs are free on the web site, but the documentation for it has to be
purchased by the user.) The VFPROC programs are DOS-based, but NGS has been
working to convert them to Windows-based programs. These Windows–based programs
are recommended over the DOS-based suite, because of better ease of use. The use of the
Windows versions will be described here.
The project managers and field crews need to be familiar with the documentation for
these programs, in addition to the NGS guidelines for vertical project submission, and of
course the FCGS specifications and the documentation for their equipment, before
starting any field work. (The documentation for NABOOK, called DvlGuide, is very
useful and has straightforward instructions for preparation and method for leveling).The
purpose of this Appendix is not to replace these other documents, but to help clarify and
highlight some of the items to pay attention to that will help the whole process move
smoothly.
Although there are several digital/electronic level manufacturers, the projects completed
so far, which are therefore the basis of this document, were all completed utilizing Leica
electronic levels (NA3003 and DNA03 models). These guidelines will address some
items specific to the Leica equipment, but overall the general process will be the same
with all brands of digital/electronic level. The CSRC is not endorsing any particular
brand of level.
Raw Level Data File Preparation
Since the vertical project will be processed according to NABOOK/VFPROC guidelines,
this means it will probably be necessary to edit the raw digital level files so that
NABOOK will be able to read the file. The documentation for the level utilized can be
used to help understand the contents of the raw file. Currently, NABOOK does not
understand the data file format produced by the new Leica DNA03 digital level. It does
understand the data format produced by the older Leica NA3003 automatic level. It is
possible to convert the DNA03 files (typically given the suffix *.GSI) to the older
NA3003 files (typically given the suffix *.RAW) using a file conversion program
(DnaGsiConverter.exe) available from Leica.
The raw file represents not only the observations made during the level circuit, but also
special codes punched into the level by the Instrument Operator. The NABOOK
documentation specifies exactly which buttons to punch, and which data items to enter
into the gun. If the raw file you’re working with doesn’t have these codes properly
entered, it will be necessary to convert them.
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In the Leica raw format, the first entry in the raw file is usually a specification as to
whether the levels are being run in single-run (backsight/foresight) mode or doublesimultaneous-run (backsight/foresight/foresight/backsight) mode. In this example, the
number “1” indicates single-run leveling:
410002+?......1
The number “2” indicates double-simultaneous leveling (410001+?......2),and this is
not permitted by NABOOK, even though it is a valid FGCS procedure for precise
leveling. If double-simultaneous levels were run, the data file will have to be converted,
with some effort, to single-run leveling. The double-simultaneous format (usually called
BFFB leveling) appears like this in the raw data file:
110017+00000379
110018+00000380
110019+00000380
110020+00000379
32..00+00037590
32..00+00037140
32..00+00037110
32..00+00037630
331168+00132005
332168+00210094
336168+00210919
335168+00132849
52..08+0003+024
52..08+0004+029
52..08+0003+013
52..08+0003+012
What you see here are four consecutive rod readings. Files of this type must be converted,
with some labor, into the files that NABOOK can read. This can be done, by extracting
the second pair of rod readings, and inserting them into a new, although fictitious, level
run which happens to have been run simultaneously with the first. However, because of
the labor involved (this really should be done using specially-designed software) and
extreme amount of data manipulation, this procedure won’t be discussed further here.
Future projects to be submitted for CSRC data processing should not be leveled
using this method.
As another example of procedural issues, Caltrans has used slightly different data-entry
routines than as required by NABOOK. The following table was provided by Caltrans,
and compares the Caltrans procedures versus the NABOOK procedures.
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CODE
INFO
1
2
11
33
99
9999
1
2
3
4
1
2
3
4
1
2
3
4
1
2
3
4
1
2
3
4
NA3003 Field Procedures
Caltrans
NABOOK
DATA
DATA
date
date
time
observer code #
wind/sun
instrument type #
observer code #
temperature code
instrument ssn
instrument ssn
collimation error (") collimation error (")
Rod 1 ssn
Rod 1 ssn
Rod 2 ssn
Rod 2 ssn
time
time
wind/sun
rod # on initial BS
survey pt. ssn
temp to .1 deg, no decimal
rod # on initial BS [blank]
lower temp probe
lower temp probe
upper temp probe
upper temp probe
temperature units
[blank]
[blank]
[blank]
date
time
time
rod # on mark
wind/sun
temperature
rod #
wind/sun code
end of obs session end of obs session
Each of these “Codes” is contained in a “41” record, however, they are not in the required
arrangement for NABOOK to process them correctly. The following example is a valid
NABOOK format:
410003+00000001 42....+00061803 43....+00000011 44....+00003003 45....+00000001
410004+00000002 42....+00092247 43....+00000016 44....+00026487 45....+00026901
410005+00000011 42....+00000835 43....+00000001 44....+00000070
What is shown here are “41” records for Codes 1, 2, and 11. These codes should follow
line 1 (410002+?......1)as described above, and should precede the observations in the
raw data file. In line 2 you see the date (June 18 2003), the observer code (11 – each
different observer gets his/her own number), the instrument type (called 3003 here,
although it was actually a DNA03) and a code indicating that the temperature
measurements were made using the Fahrenheit scale. The third line refers to the
instrument serial number, collimation error and rod serial numbers and the fourth line to
the start time, rod on mark and temperature. This information should be entered by the
instrument person as the leveling is being run and must be arranged in this order. If not, it
will be necessary to edit the data file (refer to NABOOK documentation for detailed
explanation of codes and formats).
During leveling an additional possible problem has to do with the NABOOK procedure
of requiring no earth-curvature correction and using “standard” accuracies instead of
“enhanced” accuracies. This number should be “0” (no curvature correction used and no
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enhanced accuracy) in all level runs and is set in the configuration menu in the level. You
can tell whether or not the no-curvature correction was used by looking at each rod
reading (refer to Leica instrument manual). Here’s an example:
110006+00000014 32..00+00029980 331168+00082104 52..08+0003+009
110007+00000379 32..00+00029660 332168+00163394 52..08+0003+006
The red numbers (6) in Position 5 above indicate that the reading was measured without
the earth-curvature correction, but with enhanced accuracy. This particular digit should
be 0. Consistency in field procedures should be foremost in these projects. One of the
submitted projects used varying choices in different segments of the project, e.i., in one
case both the curvature correction and enhanced accuracy were chosen, in some cases
only one of the two and in some cases neither. (The digit in the 6th place (8) indicates that
the reading itself is made to the .01 millimeter precision.)
One more requirement for the raw data file (as far as NABOOK is concerned) is that no
record may exceed 80 characters in length. Records exceeding this length will always be
empty beyond the 80th character place, and surplus characters may be safely deleted.
If the StarNetPro program was used to quality control the level run, all code 50 lines will
need to be removed, and all beginning and ending elevations set to zero, in addition to the
items described above that are needed by NABOOK.
Once the raw data file is properly formatted, it is ready to be processed into files needed
for the submission process, including preparation of description files.
Basic File Preparation for “Blue Booking”
With the raw field file from level that has been properly formatted as above, it is first run
through several steps in the NABOOK program and then through several steps in the
NGS programs. These steps have been explained in the order they need to happen. Using
VTIS, a CGPS site in Long Beach, CA. as an example, the first leveling segment was
named L266151. (Before a leveling project is started, a level line number should be
assigned from NGS, in this case L26615.) The NGS 1st order benchmark’s used for VTIS
were DY1113 and DY2502 and were given point numbers 1113 and 2502; respectively.
The number assigned to the VTIS GRM (the elevation that was to be published) was
7013 and was based on a numbering system determined with the whole project (all
segments) in mind to avoid duplicate point numbers.
1. NABOOK – install in folder called NABOOK in the C:\programs\vertpgm directory
a. Constant. exe - Choice #1 - create Header.blu file – need to know begin and
end dates of leveling, NGS codes for agencies/firms involved in project
*A1*VERTOBS CSRC CALIFORNIA SPATIAL REFERENCE CENTER
20040610
*10*L26615 1
2003090320030903MM8.0 22CALA MSPJOHFRA
2
*11*CSRC LEVELING TO 20 SOUTHERN CA CGPS STATIONS
*12*CSRC NAVD88 LEVELING TO CGPS SITE VTIS IN LOS ANGELES CO.
*15*COLLIMATION CHECK TAKEN DAILY AND STORED INTERNALLY IN THE NA3003 AND
*15*USED TO CORRECT EACH ROD READING.
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b. Constant.exe - Choice #2 - create NA.do file – need to know time zone,
number of instrument men, their instrument height and if temperature sensors
were used
*11*CSRC LEVELING TO 20 SOUTHERN CA CGPS STATIONS
(title)
T
(time zone code)
1
(no. of instrument men)
1
MSP
153
(first inst. man, initials, HI)
130
(temperature sensor default value)
30
(temperature sensor default value)
c. NABOOK.exe - move L266151.raw level file, header.blu and na.do to same
directory with NABOOK.exe and run – creates L266151.blu and
L266151.bok; check bok file for errors in level run and fix; refer to NABOOK
documentation for error code explanations
d. Copy Header.blu to top of L266151.blu file and save as L266151.txt (this file
now has header records and 40 records in it, as shown below)
*A1*VERTOBS CSRC CALIFORNIA SPATIAL REFERENCE CENTER
20040610
*10*L26615 1
2003090320030903MM8.0 22CALA MSPJOHFRA
2
*11*CSRC LEVELING TO 20 SOUTHERN CA CGPS STATIONS
*12*CSRC NAVD88 LEVELING TO CGPS SITE VTIS IN LOS ANGELES CO.
*15*COLLIMATION CHECK TAKEN DAILY AND STORED INTERNALLY IN THE NA3003 AND
*15*USED TO CORRECT EACH ROD READING.
*40*03090324391716
39622962
39623219
153130 30
-.021T0738
*41*03090311132502T07380805F64.063.012 8
KM0.484MT
1.56716MSP
*43*030903111325020738
-1.942
*41*03090325027013T08070957F63.070.002 40
KM1.121MT 51.45792MSP
*43*030903250270130807
279.394
*41*03090370132502T10031124F70.066.012 40
KM1.123MT -51.45764MSP
*43*030903701325021003
-283.362
2. WDDPROC – Install all description programs in a directory of C:\programs\vertpgm
or they will not run correctly. You also need to set a path and environment variable to
this directory as explained in the NABOOK documentation. When running these
programs all needed data files, etc. have to also be in this directory. Because
VFPROC installs all programs (*.exe) and all related program files in this directory, it
is confusing because the programs are mixed in among the documentation files,
program files, etc. For ease of use, rename them as follows (this is also the order that
you run the files through them). This puts them at the front (top) of the folder when
you open it. Each time you run a set of files through the process, you will need to
move all the required files to this directory to run them through the complete process.
You can them move them back to a project directory, for this example,
L26615_1_VTIS.
1_WDs2d.exe – need to run this on each BM used; go to web, save NGS datasheet as
*.txt file (e.i. DY1113.txt file); run 1_WDs2d - changes DY1113.txt to DY1113.dsc file;
repeat for all published marks; e.i. DY1113.dsc; DY2502.dsc; VTIS.dsc
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2_WExtract.exe – run this program on all *.dsc files created above; name with the same
name but with *_mrg.dsc as the name; e.i. DY1113_mrg.dsc; DY2502_mrg.dsc
3_WMrgdesc.exe – run this to merge the existing dsc files into one. May have to run
twice or more if you need to merge several files; e.i.:
3_WMrgdesc.exe = first : DY1113_mrg.dsc + DY2502_mrg.dsc = tempmrg.dsc
3_WMrgdesc.exe = second: tempmrg.dsc + VTIS_mrg.dsc = L266151.dsc –
which now contains all three descriptions
4_WDesc.exe – open the L266151.dsc file; go to Project; fill in all blanks and save.
(Project title should be the same as the title submitted to NGS when requesting level line
number.) If any descriptions need updating, select it and go to Description and select Edit
Description. Edit as needed and save. To add new descriptions for those marks not
previously described, go to Description and select New Description. Edit as needed and
save. Repeat as necessary. When done adding descriptions, go to File, Exit, and save
changes. Make copy of this L266151.dsc and put in project directory for safe keeping.
Note: Party chiefs should have an example of this description file with them, with the
NGS description notes so they can properly describe or at least record the needed
information. It is difficult to prepare these descriptions when you haven’t been there.
5_WChkdesc.exe – run this on L266151.dsc. View L266151.msg file with Wordpad to
see what errors exist in dsc file. Go back to 4_WDesc.exe and edit/fix errors and redo
these steps until all errors removed.
6_WPrtdesc.exe – run this on L266151.dsc and view L266151.prn with Wordpad for
final description text.
7_WinMakefile.exe – run this on L266151.txt to create the L266151.hgz file
8_WinNewabs.exe – run this program on the L266151.hgz and L266151.dsc. Need to
know beginning and ending benchmark and beginning benchmark elevation. This puts
the 30 records into the *.hgz file. This creates L266151.abs, an ASCII file to view final
results and check for errors
9_Win Readfile.exe – run this on L266151.hgz to get an ASCII file L266151.lst to view
final hgz file. Elevations should match preliminary elevations within the misclosure of
the level run (these values are not constrained to the ending benchmark at this point in the
process).
Addendum to Appendix E
After first submittal to NGS, several items from the above process were slightly revised
to accommodate the submittal of the manual measurements into the NGS database and
processing software.
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First, NGS requested that all *.dsc files (20 in all; one for each CGPS site) be merged into
one file for the whole project. This was accomplished by running 3_WMrgdesc.exe on
all 20 files to create one project dsc file, L26615.dsc.
Second, NGS requested that a separate ID be given to each possible position of elevation
on the CGPS site, the ARD, the GRM and the BPA. This required that additional
descriptions for the ARD and BPA be added to the L26615.dsc file (the original idea was
to just publish a height on the GRM of each CGPS site). To avoid confusion and possible
duplication of point numbers, each ARD was assigned the same point number as the
GRM, but with an increase of 200 and each BPA was given an increase of 100 over the
GRM. For example, the GRM for VTIS was previously assigned number 7013, so the
ARD was assigned 7213 and the BPA was assigned 7113. This convention was held for
all 20 sites. The new descriptions were created in 4_WDesc.exe by selecting the dsc file
for the GRM and creating a copy to edit for the ARD and then repeating the process for
the BPA.
NGS also wanted to better account for the manual measurements to the GRM and BPA
from the ARD (which was the only position established by leveling). They created a new
“instrument” code to be added to the inst.dat file which is used to create the *.hgz file for
processing the level run. The following example shows the inst.dat file used to process
the CGPS site level files. It includes a line for the NA3003 (in this example) and one for
the steel rule used for the manual measurements:
000010*20*24391716
000020*20*200RULE1
LEICA
UNSPECIFIED
NA3003
JOHFRA
STEEL/MM-CF JOHFRA
000000100
030000000
After this process was completed, NGS had us add extra *15 record lines to the
L266151.txt files to explain the manual measurements for each site and some additional
*40 record lines that utilized the new *20 record for the steel rule. The following example
shows the edited L266151.txt file for VTIS incorporating these additional records
(additional data lines highlighted in red):
*A1*VERTOBS CSRC CALIFORNIA SPATIAL REFERENCE CENTER
20040610
*10*L26615 1
2003090320030903MM8.0 22CALA MSPJOHFRA
2
*11*CSRC LEVELING TO 20 SOUTHERN CA CGPS STATIONS
*12*CSRC NAVD88 LEVELING TO CGPS SITE VTIS IN LOS ANGELES CO.
*15*COLLIMATION CHECK TAKEN DAILY AND STORED INTERNALLY IN THE NA3003 AND
*15*USED TO CORRECT EACH ROD READING.
*15*THE FIELD HEIGHT DIFFERENCE FOR THE SECTION BETWEEN SSNS 7213 AND 7113
*15*WAS COMPUTED AS FOLLOWS-*15* +0.2637 METER
*15*= 0.2326 METER (MANUAL STEEL RULE MEASUREMENT FROM LEVELED ANTENNA
*15*
REFERENCE DIVOT (ARD) UP TO BOTTOM OF ADAPTOR (BOA))
*15*+ 0.0311 METER (MANUAL STEEL RULE MEASUREMENT FROM BOA UP TO BASE OF
*15*
PREAMP (BPA) = MEAN ADAPTOR HEIGHT)
*15*THE FIELD HEIGHT DIFFERENCE FOR THE SECTION BETWEEN SSNS 7213(ARD)AND
*15*7013(GRM) WAS COMPUTED AS FOLLOWS-*15* +0.2554 METER
*15*= 0.2326 METER (MANUAL STEEL RULE MEASUREMENT FROM LEVELED ANTENNA
*15*
REFERENCE DIVOT (ARD) UP TO BOTTOM OF ADAPTOR (BOA))
*15*+ 0.0311 METER (MANUAL STEEL RULE MEASUREMENT FROM BOA UP TO BASE OF
*15*
PREAMP (BPA) = MEAN ADAPTOR HEIGHT)
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*15*- 0.0083 METER (FROM BPA DOWN TO GEODETIC REFERENCE MARK (GRM),
*15*
CONSTANT BASED ON MACHINING SPECIFICATIONS OF
*15*
ADAPTOR).
*40*03090324391716
39622962
39623219
153130 30
-.021T0738
*41*03090311132502T07380805F64.063.012 8
KM0.484MT
1.56716MSP
*43*030903111325020738
-1.942
*41*03090325027013T08070957F63.070.002 40
KM1.121MT 51.45792MSP
*43*030903250270130807
279.394
*41*03090370132502T10031124F70.066.012 40
KM1.123MT -51.45764MSP
*43*030903701325021003
-283.362
*40*030903200RULE1
300RULE1
300RULE1
30
T1830
*41*03090372137113T1830
F64.064.002 1
MT0.001MT0.2637
MSP
*43*030903721371131830
*40*030903200RULE1
300RULE1
300RULE1
30
T1840
*41*03090372137013T1840
F64.064.002 1
MT0.001MT0.2554
MSP
*43*030903721370131840
The *15, 40, 41 and 43 records are edited to reflect the correct manual measurements and
other site related data (point number, date, time, etc.).
After these files are prepared correctly, the L266151.txt file is run through steps
7_WinMakefile.exe, 8_WinNewabs.exe and 9_Win Readfile.exe to create the hgz file,
abs file and lst file for submittal to NGS.
This process was run on all stations and resubmitted to NGS. In the future, these steps
will be incorporated into the initial process for any level runs to CGPS sites that utilize
manual measurements as performed for this project and delineated in this document.
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Appendix F - Leveling Input For NA3003
(as required for NGS Vertical Project Submission using Charles Whalen NABook
program)
Leica/Wild NAXXXX data recording code blocks for recording single-run,
BF leveling to be processed with Whalen's NABOOK program.
Do a collimation check at start of day & set the instrument to apply it.
If error exceeds 10.0 (1st & 2nd Order) or 20.0 (3rd order) adjust
instrument & reobserve collimation check.
Code 1 - Beginning of day or change in observer/instrument/rods/or a new
collimation check
1) Date (MMDDYY)
2) Observer's code number (1, 2, or 3, etc.)
3) Instrument type number (like 2000, 2002, 3000, 3003, etc.)
4) Temperature code ( 0 for C or 1 for F)
Code 2 - Equipment used
1) Instrument serial number (like 90810)
2) Collimation error in seconds of arc (no decimal, like -58 for -5.8")
3) Rod 1 serial number (like 25458)
4) Rod 2 serial number (like 25534)
Code 11 - Start of leveling section (Set point number to 1)
1) Time (HHMM, 24 hour local)
2) Rod on mark (1 or 2)
3) Temperature (no decimal, key 75 for 75.0 degrees, omit if recording
temperatures for gradient)
(Record SPSN as point number for first backsight of each section.)
Code 22 - Reject previous backsight and foresight (No data entries)
Code 33 - Temperature (End of each setup if recording two temperatures
for gradient, else omit.)
1) Lower probe (no decimal, key 761 for 76.1 degrees)
2) Upper probe (no decimal, key 750 for 75.0 degrees)
(Record SPSN as point number for last foresight of each section.)
Code 99 - End of section
1) Time (HHMM, 24 hour local)
2) Rod on mark (1 or 2)
3) Temperature (no decimal, key 75 for 75.0 degrees, omit if recording
temperatures for gradient)
4) wind & sun codes, like 21
Code 11 for next section, etc. as above
Code 9999 - End of day or change of instrument/rod/observer/or a new
collimation check (no data entries)
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WIND
0 IF
1 IF
2 IF
CODE:
WIND SPEED AVERAGED LESS THAN 10 KM/HR (6 MILES/HOUR)
WIND SPEED AVERAGED 10 TO 25 KM/HR (6 TO 15 MILES/HOUR)
WIND SPEED AVERAGED GREATER THAN 25 KM/HR (15 MILES/HOUR)
SUN CODE:
0 IF LESS THAN 25 PERCENT OF THE SETUPS ARE PERFORMED IN SUNNY
CONDITIONS.
1 IF 25 TO 75 PERCENT OF THE SETUPS ARE PERFORMED IN SUNNY CONDITIONS.
2 IF MORE THAN 75 PERCENT OF THE SETUPS ARE PERFORMED IN SUNNY
CONDITIONS.
EXAMPLES:
FILE BEGINNING – Code 1 entries (line 1), Code 2 entries (line 2), Code 11
entries (line 3), Start leveling (line 4), First SPSN (line 5):
410001+00000001
410002+00000002
410003+00000011
410004+?......1
110005+00005358
110007+00005358
110008+00000001
110009+00000001
42....+00091003 43....+00000001 44....+00003003 45....+00000001
42....+00091716 43....-00000041 44....+00022962 45....+00023219
42....+00000757 43....+00000001 44....+00000067
83..16+00000000
32..00+00012170 331108+00103703 52..08+0004+008
32..00+00011480 332108+00193097 52..08+0004+001
573..0+00000690 574..0+00023650 83..06-00008939 (etc.)
END OF SECTION – Last SPSN (line 83), Code 99 entries (line 86):
110080+00000025
110081+00000025
110082+00000025
110083+00006353
110084+00006353
410086+00000099
32..00+00014700
573..0+00001140
32..00+00008570
32..00+00009990
573..0-00000280
42....+00000915
332108+00079758
574..0+00865780
331108+00150189
332108+00154331
574..0+00884330
43....+00000001
52..08+0004+004
83..06-00054353
52..08+0003+001
52..08+0004+004
83..06-00054767
44....+00000071 45....+00000002
BEGINNING OF NEXT SECTION – Code 11 (line 87), First SPSN (line 89):
410087+00000011
410088+?......1
110089+00006353
110090+00006353
110091+00000001
110092+00000001
110093+00000001
42....+00000918 43....+00000001 44....+00000072
83..16+00000000
32..00+00009970
32..00+00008630
573..0+00001340
32..00+00013780
331108+00156770
332108+00152634
574..0+00018600
331108+00083593
52..08+0004+003
52..08+0004+005
83..06+00000414
52..08+0003+004
END OF FILE - Last SPSN (line 549), Code 99 entries (line 552), Code 9999 (line
553):
110547+00000043
110548+00000043
110549+00000353
110550+00000353
410552+00000099
410553+00009999
573..0-00002390
32..00+00018370
32..00+00017020
573..0-00001050
42....+00001725
574..0+00889400
331108+00108149
332108+00151071
574..0+00924790
43....+00000001
83..06-00641862
52..08+0003+003
52..08+0003+008
83..06-00646155
44....+00000077 45....+00000002
Refer to manufacturer equipment documentation for explanation of proprietary data lines. Refer
to documentation for NABook program for more detailed explanation of codes and formats.
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Appendix G - NGS Procedures For Using Leica DNA03 Level (dated 04/09/04)
FIRST: Collimation test - Do first each day or at the beginning of a new project.



Press the “PROG” key, and then from the “PROGRAMS” screen select “3
CHECK & ADJUST”:
From the “CHECK & ADJUST” screen, select “1 SET JOB”
From the “SELECT JOB” screen select <NEW>
o Enter values in the “NEW JOB” SCREEN: (normally there will be one
job file for each day, if a new project is started later in the day a second Ctest will be taken and job file is created)
Job:
Oper:
Cmtl:
Cmt2:

sasmmddA
sas
blank
blank
(initials of observer, month, day, A……..B, C, D)
(initials of observer)
Then press <SET>
From the “CHECK & ADJUST” screen select “2 SET METHOD”:
o Enter values in the “SELECT METHOD” screen:
Method:
Always select A X BX
Stf1: blank
Stf2: blank Then press <SET>

From the “CHECK & ADJUST” screen, select “3 START”, Follow prompts from
screen. Then press <SET>
SECOND: Start the leveling program



From the “PROGRAMS” SCREEN, select “2 LINE LEVELING”
From the “LINE LEVELING” screen select “2 SET LINE”
From the “NEW LINE” screen enter the following: (A new line name will be
created for every section).
Name: 00010002
Meth: BF
PtID: 0001
HO: blank
Stf1: blank
Stf2: blank
Then press <SET>


(From SPSN # to SPSN #)
(Always BF, backsight-foresight)
(From SPSN #)
From the “LINE LEVELING” screen select “3 SET Tolerances”
View the “SET TOLERANCES” screen; Then if correct press <SET>
From the “LINE LEVELING” screen select “4 START”
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o On the last set-up, key in the ending SPSN # of the mark leveled to in the
comments part of the data screen.
o At this point the leveling screen will be displayed. Anytime while in the
leveling routine one can enter a code block into the job data file by
pressing the “SHIFT” key then the “PROG” key. The code screen will be
displayed and the codes will be entered as follows:
Code 1
Code 2
Code 11
Code 22
Code 33
Code 99
Code 9999
Will be entered at the beginning of the day, change in observer, or change
in instrument
Will be inserted at the beginning of the day or change in level or rods
Will be inserted at the beginning of a section
Will reject the previous back-sight and fore-sight
The temperature code will be inserted after each set-up
Will be inserted at the end of a section
Will be inserted at the end of day
LEVEL CODES
Codes are entered by pressing the shift key, and then press the user key to bring up the
function menu. Select the code function. Enter the code number and the appropriate
information for the code. Once finished, select REC and press the enter key to record the
data.
CODE 1
Beginning of Day or Change in Observer/Instrument Type
Info 1 ______________Date (MMDDYY)
Info 2 ______________Observer’s code number (1, 2, 3, etc)
Info 3 ______________Instrument type number (2000, 2002, 3000, 3003, DNA03,etc)
Info 4 ______________Temperature code (0 for C or 1 for F)
CODE 2
Equipment Used
Info 1 _______________Instrument serial number (like 90810)
Info 2 _______________C test error in seconds of arc (no decimal, like –58 for –5.8)
Info 3 _______________Rod 1 serial number (like 25458)
Info 4 _______________Rod 2 serial number (like 25534)
CODE 11 Start of Leveling Section
Info 1 _______________Time (HHMM, 24 hour local)
Info 2 _______________Rod on mark (1 or 2)
Info 3 _______________Temp (no decimal, key 750 for 75.0 – leave blank if a
thermister is used)
Info 4 _______________No entry
CODE 22 Reject Previous Back-sight and Fore-sight
Info 1 – No entry
Info 2 – No entry
Info 3 – No entry
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Info 4 – No entry
CODE 33 Temperature Gradient
Info 1 _______________Lower Probe (no decimal, key 761 for 76.1)
Info 2 _______________Upper Probe (no decimal, key 761 for 76.1)
Info 3 No entry
Info 4 No entry
CODE 99
End of Section
Info 1 ______________Date (MMDDYY)
Info 2 ______________Observer’s code number (1, 2, 3, etc)
Info 3 ______________Temp if thermister not used (756 for 75.6, leave blank if a
thermister is used)
Info 4 ______________Wind & Sun code
Wind Code:
0 - if wind speed averaged less than 6 mph
1 - If wind speed averaged 6 to 15 mph
2 - If wind speed average averaged greater than 15 mph
Sun Code:
0 - if less than 25% of setups are performed in sunny conditions
1 - If 25 t0 75% of setups are performed in sunny conditions
2 - If more than75 % of setups are performed in sunny conditions
CODE 9999
End of Day or Change of Observer
Info 1 ______________ Leave blank
Info 2 ______________ Leave blank
Info 3 ______________ Leave blank
Info 4 ______________ Leave blank
DNA03 LEVEL SETTINGS
The following settings can be set from the “Meas & Rec” screen. This screen comes up
when the level is first turned on. If the level is in the “PROGRAM” mode, exit the
program to see the “Meas & Rec” screen.
SET MEASUREMENT MODE


From the “Meas & Rec” screen, press the MODE key.
From the “MEASURE MODE” screen, set the following to:
Mode: Mean s
N:
blank
N Min:
3
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N Max:
10
SdevM / 20m: 0.00002
Highlight < SET > then press the red key.
SET CURVATURE CORRECTION OFF




From the “Meas & Rec” screen: Press the SHIFT PROGRAM keys.
From the “MENU” screen, select “ 2 ALL SETTING” then press the red key.
From the “ALL SETTINGS” screen, select “ 2 MEASURING” then press the red
key.
From the “MEASURING SETTINGS” screen, set the following:
Codeset:
Decimals:
GSI-Format:
EarthCurv:
Before
0.00001
GSI – 8
No
Highlight < SET > , then press the red key
SET UNITS




From the “Meas & Rec” screen: Press the SHIFT PROGRAM keys.
From the “MENU” screen, select “2 ALL SETTING” then press the red key.
From the “ ALL SETTING”screen, select “ 4 UNITS” then press the red key.
Set to “Metre”, then select < SET >, then press the red key.
SET DATE AND TIME



From the “Meas & Rec” screen: Press the
SHIFT
PROGRAM keys.
From the “MENU” screen, select “ 2 ALL SETTING” then press the red key.
From the “ ALL SETTING”screen, select “ 5 DATE/TIME” then press the red
key.
Set the date and time. Then select < SET >, then press the red key.
SET INCREMENT MODE


From the “Meas & Rec” screen: Press the SHIFT USER keys.
From the “FUNCTIONS” screen , select “4 PtID & Increment”
Set the following:
PTID: 1
INCR: 1
Select < SET > then press the red key.
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