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Manual GCP Adjustment Result

GCP Manual correction works well. Started with a mean 15.2-ft horizontal error (0.5-ft Std Dev.) and after adjustment, I get a mean 0.5-ft horizontal error (0.2-ft Std Dev.). Question-1: Is this the post-adjustment horizontal error I should expect?

Question-2: how do I get elevation error values? I'm using GE Pro for ground truth, so I get the elevation with GCP's. But how can I get elevation values for the MME map to compare with ground truth?

Felton Flood

Official comment


We apply a thin plate spline (rubber sheeting) to the GCP locations so the error should be near zero there. So those numbers are a bit high but if you are measuring points away from the GCP they are reasonable. 

We do not make any morphological corrections to the initially computed model. Offset and/or tilt is applied to minimize the elevation error at the GCP locations but there is no correction for barrel distortion or swelling.

To check the values you can simply mouse over the location in the Maps Made Easy web map to see the elevation value. Or you could use the DEM itself. 

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