DerrickW

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DerrickW
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  • Gridding and Contouring options

    Best "suggestion" post I've read on these forums.  Love it. 
    TRB426
  • Using Check shot GCPs

    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. 
    TRB426
  • Creating a surface with the same shape as the terrain

    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. 
    kfroese