Traditional RTK sur...
 
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Traditional RTK survey- What should I have entered for my base point?

awhaling
(@awhaling)
FNG Member

Hello all, I could really use some help correcting an error in setting up my Trimble R10 base and rover for a traditional RTK survey.  I had the base set-up on a benchmark and used the rover in continuous topo mode to interface with an echosounder for a bathymetric survey.  The problem is that I thought I was being clever by not selecting a geoid model in my TSC3 with the idea that the rover would output ellipsoidal heights and I would apply a geoid in post-processing.  Well, that might have worked except I did not realize that I should have put in an ellipsoidal height into the base height instead of an orthometric height.  Aside from that problem, I'm afraid the horizontal information I entered for the base point is wrong too.  I entered Nad83 11 positions in UTM, when maybe in should have been Nad83 86 based on the job properties (?).  I was hoping someone could look at the job properties for my collected data (below) and tell me what I should have entered for my base point.  I'm equally as confused about what I should have entered for the vertical in the base point even if it was supposed to be an ellipsoidal height.  I selected WGS84 as the vertical datum, so should I have entered a WGS84 transit ellipsoid height or WGS84 G1150 ellipsoid height or something else?  Any help on this is much appreciated.

Projection

Projection Universal Transverse Mercator
Origin lat 0°00'00.00000"N
Origin long 81°00'00.00000"W
False northing 0.000
False easting 500000.000
Scale 0.99960000
Ellipsoid Semi-major axis: 6378137.000 Flattening: 298.25722154

 

Local site

Type Grid

Datum transformation

Type Three parameter
Semi-major axis 6378137.000
Flattening 298.257223
Translation X 0.000
Translation Y 0.000
Translation Z 0.000

Coordinate system

System UTM
Zone 17 North
Datum NAD 1983 (Conus)
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Topic starter Posted : December 19, 2019 9:05 am
Rover83
(@rover83)
1,000+ posts Member

RTK is relative positioning. Essentially, it's up to you (and your project requirements).

If your base station has published values in a specific datum/projection, either use those values or convert to the desired datum.

If you wish to use orthometric elevations, apply the appropriate geoid for your datum, whichever one you choose.

Make sure you document everything in the metadata...

 

EDIT: I didn't provide much practical information. I assume you are using TBC for post-processing? It is a matter of setting up the project coordinate system to the datum/realization/geoid you want your data to be in, then creating a control-level coordinate for a point (ideally named the same as your base point in your field data) with the published values. Then, import your JXL/JOB file, and merge the base point with your user-entered control point. Delete the coordinate record that came in from the job file, then recompute. Voila, your data is now on whatever datum you chose!

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Posted : December 19, 2019 12:34 pm
BStrand
(@bstrand)
1,000+ posts Member

I think you should have just tapped the here position button and went about your business.

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Posted : December 19, 2019 1:28 pm

awhaling
(@awhaling)
FNG Member

@rover83

Thanks for the response.  So that I understand, you are saying that it doesn't matter what I "told" the TSC3 (ie the job properties above).  All that matters is what datum I put my base point in? In other words, the datum I entered my base point as is the datum my data is in?

FYI I am not editing with Trimble software.  The position and elevation from the rover data gets integrated with the depth data at the echosounder unit.  One data stream gets sent from the echosounder to a computer which a software package then logs.  I then go on to post-process with this software.  The software expects data to be coming in as WGS84 transit... I had selected WGS84 as the datum in the Trimble thinking that would ensure my data is in WGS84 transit.  However, now that I am in the weeds with it, I'm really unsure now if by selecting WGS84 as the datum, that this is actually referring to WGS84 G1150 or whatever GPS is currently using, not transit.  Maybe none of that matters though as long as I entered my base point as WGS84 transit?  Thanks.

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Topic starter Posted : December 19, 2019 2:02 pm
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