I'm looking for opinions and suggestions on methods for GPS surveying of Aerial panels and control for a design topo and boundary survey.
Mainly I am interested in what is an appropriate duration and number of static observations. Currently we typically occupy static observations 2 times for 20 minutes at least 45 minutes apart.
We are using Leica GS15 receivers.
What processes do others use to establish Aerial control, project control, adjustments, etc?
Also, I am interested in any helpful literature, courses or books that you could suggest on GPS surveying techniques. I am hoping to buy Jan Van Sickle's fourth edition of GPS for Land Surveyors soon. I want to become more confident and experienced in the use of GPS.
Here is a picture of a typical project I would be planning for. Thanks in advance for all the wisdom
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KellyJohnson, post: 422232, member: 1332 wrote: Currently we typically occupy static observations 2 times for 20 minutes at least 45 minutes apart.
I'd have no problem with using RTK for that. Two sets of observations (for up to 3 minutes, ie/until coordinate quality is optimized) with a time separation, and LS adjust.
Here is one resource:
http://csrc.ucsd.edu/docs/CLSA_CSRC_GNSS_Standards_and_Specifications_v1.1.pdf
You might consider mixing static with RTK. I'd suggest doing 20-30 minute static sessions first. You could then post-process, set your RTK rover to stakeout and shoot the panel points at a time different from the static session. LGO will automatically create an "Average" coordinate triplet. As an additional check, you can obtain OPUS RS solutions.
It's quicker than two static sessions and will give a feel for how the GS15 handles possible multipath issues in urban areas. I really like those units. Wish I could afford to own rather than rent. With my budget, I use 5 Leica SR530s for static GPS with LGO and OPUS Projects.
Mark Mayer, post: 422237, member: 424 wrote: I'd have no problem with using RTK for that. Two sets of observations (for up to 3 minutes, ie/until coordinate quality is optimized) with a time separation, and LS adjust.
Thank you for your response, Mark. How about grid or ground coordinates? Would you apply a combined scale factor to obtain ground distances before utilizing for Photogrammetry?
While we havent set aerial targets in a very long time. If those are also main control points I would generally do as you described. Depending on the number of receives and people in the field I would plan your triangulation start and stop times to ensure you have at least two usable baselines between each point, keeping in mind the trivial baseline rule...if you follow it. Process and adjust your network.
KellyJohnson, post: 422249, member: 1332 wrote: How about grid or ground coordinates? Would you apply a combined scale factor to obtain ground distances before utilizing for Photogrammetry?
Here in Portland I'd be using a low distortion projection (OCRS-Portland Zone), so the grid/ground issue pretty much goes away. If I were elsewhere I'd supply state plane coordinates. And I'd make a clear statement about it, in writing, including a project convergence angle and combined scale factor. Users of the mapping can apply those factors to their xrefs if they choose to. They won't.
SPMPLS, post: 422241, member: 11785 wrote: Here is one resource:
http://csrc.ucsd.edu/docs/CLSA_CSRC_GNSS_Standards_and_Specifications_v1.1.pdf
Thank you, lots of great information here.
First, for your scenario, you need two receivers at least. Three would be better. All L1/L2 gear and have one act as a base and process static vectors from the base station. If you can't, then you have to consider the distances to the reference stations. 20 minutes may not be long enough, but based on that amount of urban environment, I'd say CORS should be pretty handy.
The reason you want at least two is that you're processing multiple vectors at once and can then begin to build a network. The receivers must run at the same time and tract the same SV's so that the baseline can be processed between them and then ran through the adjustment.
Building a network with static GPS is no different than building a network with total stations. You need to do a lot of extra work to ensure the control is tight. The methods are the only difference.
As far as grid/ground, that may not be an issue. In my little neck of heaven, I'm less than 500' MSL (mostly) and within 20 miles of the zone line. That being said, grid is very nearly ground and in some towns, it's on a magnitude of 0.01'/mile different. That's good enough for everyone I know to stay on the grid and not molest the coordinates.
If you're higher than 800' and in the middle of an SPC zone, then your mileage may vary. Google Earth can provide you Lat and Long and elevation and you can crunch the numbers via the NGS toolkit using GEOID12A and SPC utilities to compute the CSF for the project. From there you can decide whether or not you need surface or grid stuff. Or, go with a LDP, but I have better things to do than design one of those every time I hit a new project so I stay on the grid.
