Global Mapper Pro

Subtracting two elevation layers that don't overlap

I have two elevation layers (that don't overlap in all areas) that I want to compare. When I compare (subtract) the two layers the areas that don't overlap don't show up. Can I set it up so that if there is no data in one layer then it treats that as zero. Eg first layer has no data, second layer has value (depth) of 0.3m. When I subract the two layers I would like that to show as -0.3. ie the depth at that spot decreased by 0.3m.



  • Hi AFG - sorry I don't fully understand the last part of your question? Perhaps you could post a stripped down package file or even some screen grabs of what you are trying to do...?

    As far the first part goes, you could bound the limits of your second (larger) surface data using Create Coverage Area (Convex Hull), then convert that area into a Terrain at elevation 0 mRL and finally combine your first (smaller) surface with the 0 mRL surface (using Combine/Maximum Elevation option) . That way you will end up with a combined surface that comprises your first (smaller) surface and with the surrounding area at 0 mRL.   

    As far as the second part foes, who knows?

  • Sorry, "goes" not "foes"
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