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Consistency issues with DSM

I’m having tremendous difficulty generating consistent surface data. 

To briefly summarize, I have:

  1. Flown multiple flights over the same location

  2. Set GCPs using survey grade GPS equipment.

  3. Independently processed individual flights using same GCP points.

  4. Found significant surface variations (Z values) where no surface change has occurred between flights. 

Can anyone please explain the variation between surface data?  I’ve tried to limit as many external factors as possible (Used same .afp mission for all flights, flights conducted under similar weather conditions and wind direction, similiar # of photos used for processing, etc.). 

Hi Madison,

That’s very strange indeed.   Are your Z variations in locations outside the area “covered” by the GCP’s?

The model will not have accurate elevations in areas outside the GCP’s. 


My next thoughts would be do you have enough overlap and Tie Points?


Variations are within the GCP area, but I believe I’ve figured out the problem. 

I’ve been using the MSL (egm96) option for my vertical coordinate output.  It appears this option is very inconsistent.  After calculating the Geoid Height above Ellipsoid and using this option for vertical output my resulting data has been more consistent.