Projections and Datums within
ArcGIS
Melita Kennedy
2012 Datum Series Sponsored by GPSMMS
Subcommittee
This is the third webinar in a 3-part Series on Datums.
1)
Datum Primer – Dave Doyle*
2)
GPS Software Datums - Joel Cusick / Alison Walker (Nov 18)**
3)
Projections and Datums in ArcGIS – Melita Kennedy (Dec 17)***
Tim Smith Chair; Joel Cusick Co-Chair
* http://www.anymeeting.com/tgadgets/EC51DA87854B
** - Sharepoint Site – Datum Webinars
*** - This Webinar Sharepoint Site – Datum Webinars
Topics
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Esri projection engine
•
Coordinate systems
•
Transformations
•
Future work
•
Review
Esri Projection Engine
Esri projection engine
•
One universal library for all ESRI products
pe.dll
- Not tied to just one product
-
•
Improve maintenance/ease of programming
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Speed, consistent results, standardization
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Accuracy – tight forward/inverse round trips
-
•
Must have inversibility
Engine versus Factory
PE library sections
•
Engine
Objection creation & processing
- Transformations
- Projections
- Math functions
-
•
Factory
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Predefined objects
-
-
Coordinate systems, ellipsoids, units, etc
Well-known ID lookup
Number of Objects in PE Factory
•
10
Angular Unit
•
607 Datums
•
57
Linear units
•
635 GCS
•
217
Spheroids
•
1240 Geographic Transforms
•
15
Prime Meridians
•
44
Parameters
•
3567 PCS
•
14 Geographic methods
•
117 Vertical Datums
•
2 Horizontal methods
•
124 VCS
•
9 Vertical methods
•
•
74 Projections
•
47 Vertical Transformations
17 Horizontal/Vertical CS
Total = 6796 at 10.0
Number of Objects in PE Factory
•
10
Angular Unit
•
644 Datums
•
59
Linear units
•
671 GCS
•
218
Spheroids
•
1375 Geographic Transforms
•
15
Prime Meridians
•
44
Parameters
•
4289 PCS
•
14 Geographic methods
•
126 Vertical Datums
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2 Horizontal methods
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133 VCS
•
9 Vertical methods
•
•
76 Projections
•
69 Vertical Transformations
17 Horizontal/Vertical CS
Total = 7771 at 10.1.1
Coordinate Systems
ArcGIS 10.1 coordinate systems
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Coordinate system definitions always stored in library
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‘prj files’ installed separately
•
At 10.1 over 5000 files
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Now store the folder information in the library
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Display a ‘virtual’ directory structure
NAD 1983 and variant support
•
•
GCS, UTM zones, SPCS zones, Albers
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NAD 1983
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NAD 1983 HARN
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NAD 1983 CORS96
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NAD 1983 NSRS2007
NAD 1983 (2011) + UTM zones
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State Plane zones in 10.1.2
ArcGIS 10.1 coordinate systems
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User interface updated
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‘Layers’
•
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Listed each layer
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Open to see its coordinate system
Now list each coordinate system
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Open to see which layers use it
spatial filter
favorites
create or import
coordinate system
search
well-known ID
Coordinate system search and filter
•
•
Spatial filter
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Current extent
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Layer extent (any in the map)
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Custom extent
Search/filter by
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Name
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Only folders that contain matches will be shown
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Well-known ID (WKID) aka 4326, 26906
Favorites
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Now visible (and usable) everywhere
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Stored in your user profile
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C:\Documents and Settings\melita\Application Data\
ESRI\Desktop10.1\ArcMap\Coordinate Systems
(Windows XP)
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Supports folders
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Import coordinate system from
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Data
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Prj file
NEW
Coordinate
System
Demonstration
Transformations
Geographic transformations
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‘Datum’ transformations
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Convert between GCS
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Includes unit, prime meridian, and spheroid changes
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Defined in a particular direction
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All are reversible
Transformation methods
•
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Equation-based
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Molodensky, Abridged Molodensky, Geocentric Translation
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Coordinate Frame, Position Vector, Molodensky-Badekas
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Longitude Rotation, 2D lat / lon offsets
File-based
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NADCON, HARN, NTv2
ArcMap 10.1 transformations
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Sorted by applicability
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Area of use
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Accuracy
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Will create compound (two-step) transformations
automatically
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Ex. NAD_1927_To_NAD_1983_NADCON +
NAD_1983_To_WGS_1984_5
Combined transformations
ArcMap 10.1.1 transformations
•
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NAD_1927_To_NAD_1983_NADCON
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ArcMap default
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Until 10.1.1
No more default transformations!
Transformation metadata
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Areas of use
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Accuracy
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C:\Program Files\ArcGIS\Desktop10.1\Documentation\
geographic_transformations.pdf
http://support.esri.com/en/knowledgebase/techarticles/detail/21327
Methods in Alaska
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Coordinate Frame
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Equation-based
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Seven parameters
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3 translations, 3 rotations, 1 scale factor (in XYZ)
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NAD_1983_To_WGS_1984_5
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WGS_1984_(ITRF00)_To_NAD_1983
NADCON / HARN
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File-based
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Generally most accurate
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NAD_1927_To_NAD_1983_Alaska
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No transformations released for current adjustments
Transformations with same parameters (1)
Officially, NAD83 (CORS96) to ITRF96*
•
NAD_1983_To_WGS_1984_5*
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NAD_1983_HARN_To_WGS_1984_3
Source: http://geodesy.noaa.gov/CORS/coord_info/
coordtrans_no_support_tables.shtml
*Paper:
http://www.ngs.noaa.gov/CORS/Articles/SolerSnayASCE.pdf
Table 1, page, 51, Last column
_5 is Default for DNRGPS
And ArcGIS prior to 10.0
Transformations with same parameters (2)
Officially, ITRF00 to NAD83 (CORS96)
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ITRF_2000_To_NAD_1983_CORS96
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ITRF_2000_To_NAD_1983_HARN
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ITRF_2000_To_NAD_1983_2011
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WGS_1984_(ITRF00)_To_NAD_1983_HARN
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WGS_1984_(ITRF00)_To_NAD_1983_CORS96
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WGS_1984_(ITRF00)_To_NAD_1983_2011
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WGS_1984_(ITRF00)_To_NAD_1983
Source: http://geodesy.noaa.gov/CORS/coord_info/
coordtrans_no_support_tables.shtml
NGS CORS past coordinates website
http://geodesy.noaa.gov/CORS/coord_info/coordtrans_no_support_tables.shtml
Paper: http://www.ngs.noaa.gov/CORS/Articles/SolerSnayASCE.pdf
Table 2, page, 52
Transformations with same parameters (3)
ITRF08/WGS84 transformations
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ITRF_2008_To_NAD_1983_2011
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WGS_1984_(ITRF08)_To_NAD_1983_2011
Pacific Plate
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ITRF_2008_To_NAD_1983_PA11
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WGS_1984_(ITRF08)_To_NAD_1983_PA11
Marianas Plate
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ITRF_2008_To_NAD_1983_MA11
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WGS_1984_(ITRF08)_To_NAD_1983_MA11
Source: http://www.ngs.noaa.gov/CORS/coords.shtml
NGS CORS coordinates website
http://www.ngs.noaa.gov/CORS/coords.shtml
Bookkeeping transformations
Parameters are zeroes!
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ITRF_2000_To_WGS_1984
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NAD_1983_CORS96_To_NAD_1983_HARN
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NAD_1983_CORS96_To_NAD_1983_NSRS2007
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NAD_1983_CORS96_To_NAD_1983_2011
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NAD_1983_HARN_To_NAD_1983_NSRS2007_1
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NAD_1983_HARN_To_NAD_1983_2011
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NAD_1983_NSRS2007_To_NAD_1983_2011
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NAD_1983_NSRS2007_To_WGS_1984_1
Geographic
Transformation
Demonstration
Current and Future Work
Geodetic features
•
•
Editing
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Advanced Editing toolbar
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Lines, circles, and ellipses
Geoprocessing Tools
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Bearing Distance to Line
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XY to Line
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Table to Ellipse
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Buffer
-
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Geographic coordinate system
Calculate Grid Convergence Angle
Geodetic features
•
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Types
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Geodesic
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Great circle / great elliptic
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Rhumb line / loxodrome
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Normal section
Measure tool
Future work
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Vertical transformations
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Customizable ‘factory’
-
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Limited selection of coordinate systems and transformations
14 parameter (time-based) datum transformations
Vertical transformation methods
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Vertical Offset
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Vertical Offset and Slope
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VERTCON
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Geoid models
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EGM84, EGM96, EGM2008
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US geoid models
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Generic model/file type for user-defined ones
14 parameter time-based transformation
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Base 7 parameters are updated based on velocity values
Review
Review:Datums Change
WGS84/ITRF
Sats
ITRF00
Base Provider
Export Using
NAD83(CONUS)CORS96
GIS
SSF
COR
SHP
How to Do it
•
In Garmin Workflows with DNRGPS (Formerly DNRGarmin)…
•
Tag all your data as “plain vanilla” “NAD83”
Exported
Coordinate
System:
Use this POSC Code:
Use this PRJ
Alaska Albers
3338
NAD 1983 Alaska Albers
(Meters).prj
UTM Zone 8
26908
NAD 1983 UTM Zone 8N.prj
GCS NAD83
4269 (no projection
GCS NAD 1983.prj
How to Do it
•
In Pathfinder Office, select the Projection file to match the
Exported Coordinate System.
•
Today tag your CORS corrected data to “CORS96” NAD83
Exported
Coordinate
System:
Use this PRJ File:
Alaska Albers
NAD 1983 (CORS96) Alaska Albers (Meters).prj
UTM Zone 8
NAD 1983 (CORS96) UTM Zone 8N.prj
GCS NAD83
NAD 1983 (CORS96) prj
How to Do it
•
In ArcGIS *Assuming the standards of how the data “got to
NAD83” were followed…
Convert from:
Into GCS_NAD_1983_CORS96 use:
GCS_North_American_1983
None
GCS_WGS_1984
Garmin/DNRGPS:
Go Into GCS_NAD83 only
Mapping Grade:
WGS_1984_(ITRF00)_To_NAD_1983_CORS96
GCS_North_American_1983_HARN
NAD_1983_CORS96_To_NAD_1983_HARN
Conclusions
•
As spatial references continue to evolve, it is important
to understand how such evolution affects the Mapping
software that we use for collecting and processing GPS
data.
•
As we navigate to previous GPS datasets or update them
(at submeter), it is extremely important to transform
properly to get back to the right place
•
Options in the field and office GPS software can change
the spatial reference of the GPS data that we collect.
•
Esri software options can also change the spatial
reference of any GPS data we collect.
•
Knowing how these changes occur can eliminate much
confusion and lead to satisfactory positioning results.
References
•
Soler, T. & R.A. Snay (2004). Transforming positions and
velocities between the International Terrestrial Reference
Frame of 2000 and North American Datum of 1983, J. Surv.
Engrg., ASCE, 130(2), 49-55.
http://www.ngs.noaa.gov/CORS/Articles/SolerSnayASCE.pdf
•
Trimble, “GPS Pathfinder Office Software or the GPS Analyst
Extension: Resolving the NAD 83 Datum Transformation
Issue,” [online].
http://trl.trimble.com/docushare/dsweb/Get/Document170369/SprtNote_PFOGPSA_NAD83Datum.pdf
•
Dr. Richard Snay is Retired Manager of the National
Continuously Operating Reference Station (CORS) program
and a geodesist with the National Geodetic Survey
•
http://support.esri.com/en/knowledgebase/techarticles/detail/
21327
Questions?
Thank you!