How accurate do your GCP LAT and LON measurements need to be for manual corrections? I'm using a Trimble Catalyst in High Precision mode. On a good day can get 10 -15 cm accuracy, on a poor day or with obstructions 30 - 45 cm accuracy. I almost never get the advertised 1-2 cm accuracy. So what is the breakpoint where it's just not worth trying to use the GCPs?
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Garbage in Garbage out. The GCPs will be aligned with a minimized error. Small adjustments are made in the X and Y directions. We use a thin plate spline adjustment process which keeps it from having to be a fixed offset.
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Since I sent that post I have refined the use of my Catalyst GPS and now am able to consistantly get 3-4 cm accuracy. Having said that, once I have corrected a map with GCPs how do I determine the absolute and relative accuracy for any given map that I have produced w/ MME?
Gary
One way would be to load your ortho into QGIS (or other capable program) and check the coordinates of your GCP's and those of your check-shots against their known location.
At the time you move the markers that get loaded from the GCP file you will move them around on the map to line up with the marked locations. At the bottom there is a table that will show how far each marker is from its original location.
When you open the GCP adjusted version of the map the locations of the GCPs will have the markers drawn on them. You can use the linear measurement tool to measure the distance from the marked locations and the markers. It will likely be too small of a distance to measure using that tool though and loading it into 3rd party software will likely be the only option to make the error measurements.
