VRS Baselines in Trimble and Least Squares
I have been working with Starnet and least squares and was wondering about the baseline data received from a Trimble data collector and an RTK CORS baseline. I work around the twin cities in Minnesota and regularly use the state??s network and wanted to get my thinking straight regarding the following issues. I found that I hit some roadblocks trying to explain this to people.
A number of years back I contacted an individual at the state to inquire about how the system worked. He told me that the network generates a VRS which acts as the base station. I was wondering why, in the Trimble software, a base point appears at a known mount point typically miles away from a survey. Shouldn??t the software generate a point where the VRS is located, since that is the base? He did not have an answer for me other than that is just the way the Trimble software works. Does other software do the same thing?
Also, when the system switches to a new base and has to reconnect, I assume that this means a new VRS is being generated. Why then is another base point at a different mount point displayed? Technically these are mount points and not the actual base point(s), right? That would mean adjusting the baselines from the Trimble report would be meaningless, never mind the lousy network geometry.
When doing least squares baseline adjustments with a static operation or an RTK operation using your own base station and not CORS/VRS, the baselines are essentially point to point and roughly within the realm of the site that you are working on. This does not seem to be the case with the CORS in my mind. The base lines are all radiating from the mount point(s) miles away in most cases and not from the VRS, which should be the actual base point and somewhat close to the site you are working on, right?
Another thing I noticed is that if you apply the deltas (xyz) between a mount point and any measured point, there is a transformation error of some kind. What causes that? It seems like I should be able to back calculate the GPS baselines from a Trimble report and find a location as I can with the total station data, but that does not seem to be the case. This occurs when applying a least squares to the baselines as well, obviously it??s just using the report, but it seems that there is some missing data there.
Any clarification would be appreciated, Thanks.
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