DerrickW

Best "suggestion" post I've read on these forums.  Love it. 

dpitman said:

Hi Folks,

I don't yet have GM.

In GM, how do you examine the coordinates of check shots to compare them to surveyed values?

Thank you,
Dave

Like a point to point inverse?  Not sure how to do that in global mapper, as I normally do that in CAD.  

Since you're using the term "GCPs", I'm assuming that you're a drone user.   The way I compare checkshots to my drone-derived DSM/DTM is: 
1: Import GCPs
2. Use calculate/copy attributes tool to copy "ELEVATION" attribute to a new attribute called "Observed"
3. Turn on DSM/DTM layer if it's not already on
4. Select all checkpoints and right-click--->analysis---> apply elevations to features
5. Use calculate/copy attributes tool to copy "ELEVATION" attribute to a new attribute called "Predicted"
6. Use calculate/copy attributes tool with the formula OBSERVED - PREDICTED, and write it to an attribute called "Delta"
7. change display labels to "Delta" attribute.  Export as CSV to calc RMSE, if needed. 

You can also convert the DSM/DTM to a point cloud (or "Create points at elevation grid cell centers") and use the lidar QA/QC tool.   The lidar tool will sample nearby points.  The workflow above will sample a single cell/pixel at the same XY coordinates as your control point. 

Above advice is good, but I take it a step further by converting the elevation grid to points and then creating a bounding box that's point-to-point from that.  Prevents the weird triangles from being created along the edge of the cropping polygon.