UNIVERSITY OF SOUTH ALABAMA
Once upon a time…..
The Alidade and Plane Table Surveying
GY 301: Geomorphology
Lecture 10: Total Station Surveying
Measurements with the Alidade and
Stadia Rod
Alidade & Plane Table
• Stadia Rod: usually a 10 foot rod with feet
and 0.1 foot divisions painted on the rod
http://www.harborfreight.com/cpi/photos/96600-96699/96669.gif
An early model alidade
http://www.hugha.co.uk/Tanzania/TanReporter52_files/LR006.jpg
Ray Measurement Geometry
Geometry of Alidade Measurements
• Stadia intercept: distance on rod from lower to upper
horizontal stadia line; distance ratio is 1:100
•
ALIDADE STADIA CROSS HAIR
full stadia
intercept
•
•
Measurements from the alidade station to a data point are termed rays
The ray is drawn on the plane table to track distance and direction, and the
elevation of the ray endpoint is calculated in field notes
A correction must be made for the difference between the alidade cross hair (CH)
intercept and the instrument height (IH) of the alidade (see below):
vertical cross hair
10
IH=3.5ft
half stadia
intercept
horizontal cross hair
9
8
quarter stadia
intercept
Cross hair (CH)
= 5.7ft
quarter interval
cross hair
stadia rod
stadia intercept = 9.9 - 7.5 = 2.4 feet
distance = 2.4 x 100 = 240 feet
http://nationalatlas.gov/articles/government/IMAGES/usgs_topographer.gif
5.7ft
Elevation=161ft
Elevation @ Rod = 161ft + (IH-CH)
= 161ft + (3.5ft-5.7ft)
= 161ft – 2.2ft
= 158.8ft
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Alidade Mapping Strategy
• You should not try to shoot a ray > 250ft
with the alidade unless you have no choice
• Moving the alidade from one station to
another station is “traversing” the instrument
• You should shoot rays to all needed control
points around the 1st station, then shoot the
last ray to the new 2nd station position
• You will need to calculate the elevation at
the new 2nd site, and start a new data sheet
with a new instrument height recording
• Since you are to produce a topographic map
you may need supplemental elevation
control points in addition to the feature that
you are mapping (geological contact,
building plan, etc.)
Today’s Agenda
The Total Station
Benefits and Downfalls
The instrument
R2
R1
R3
ST1
R4
R7
ST2
R5
R6
Total Station
• Electronic version of Alidade
• Accurate to ±3 ppm horizontal & vertical
Total Station Advantages over the Alidade
• Calculations are processed internally so there are no
post data collection calculations to process
– 3x10-6 (5000 feet) = 0.2 inches
Total Station Advantages over the Alidade
• Calculations are processed internally so there are no
post data collection calculations to process
• Accuracy is much better than alidade, and it is not
shot distance dependent
Total Station Advantages over the Alidade
• Calculations are processed internally so there are no
post data collection calculations to process
• Accuracy is much better than alidade, and it is not
shot distance dependent
• Results are stored in a data collector computer that
can display results graphically
http://www.iwitnessphoto.com/iwitness/images/yellow_marks.jpg
http://www.mohaveinstrument.com/NewSite%20Folder/NewSite.data/Components/SET30RK-2.jpg
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Total Station Advantages over the Alidade
Total Station Disadvantages
• Calculations are processed internally so there are no
post data collection calculations to process
• Accuracy is much better than alidade, and it is not
shot distance dependent
• Results are stored in a data collector computer that
can display results graphically
• Each individual ray shot can take as little as a few
seconds to take- many more stations can be collected
per day as compared to the alidade and plane table
method
• No plane table for sketching contours and/or contacts
on a geologic map
Total Station Disadvantages
Total Station Disadvantages
• No plane table for sketching contours and/or contacts
on a geologic map
• It may take 30 minutes to an hour to set up (level) the
instrument before data can be collected
• No plane table for sketching contours and/or contacts
on a geologic map
• It may take 30 minutes to an hour to set up (level) the
instrument before data can be collected
• Battery life on data collector computer can limit
length of daily surveys
http://farm1.static.flickr.com/53/188809327_dea5af9bef.jpg
Total Station Surveys
Total Station Surveys
• The initial XY coordinate system of the instrument is
random- it must be calibrated to conform to
geographic or magnetic north
• The initial XY coordinate system of the instrument is
random- it must be calibrated to conform to
geographic or magnetic north
• A “backsight” target is established north of the
starting station position to calibrate coordinate system
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Total Station Surveys
• The initial XY coordinate system of the instrument is
random- it must be calibrated to conform to
geographic or magnetic north
• A “backsight” target is established north of the
starting station position to calibrate coordinate system
• If two benchmarks or former station positions have
known coordinates the relative positions can be used
to calibrate coordinate system
Total Station Instrument
Setting up the tripod
http://z.about.com/d/archaeology/1/0/s/F/total_station.JPG
Total Station Instrument
Total Station Instrument
Setting up the tripod
Setting up the prism
http://z.about.com/d/archaeology/1/0/s/F/total_station.JPG
Total Station Instrument
http://z.about.com/d/archaeology/1/0/s/F/total_station.JPG
Total Station Instrument
Packing/unpacking the instrument
http://www.tricountytransit.com/sitebuilder/images/totalstation1-759x536.jpg
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Total Station Instrument
Total Station Output
Data recorder
http://www.umt.edu/geosciences/faculty/hendrix/g429/images/Farlinmap4.jpg
Upcoming Stuff
Homework
GPS Data processing (Lab 4 due a week Friday)
Signup for data transfer/software instruction
Next Lecture:
Total Station setup demonstration
Friday’s Lab:
Outside: Total Station survey (meet first in LSCB 042)
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