Global Mapper Pro

Mixing bathymetry and elevation data

Michael_GR Global Mapper User
I have two data sets, one is a bathymetry elevation file in which the below-sea-level data is correct but all above-sea-level data is zero, and a "normal" elevation file in which the opposite is true. Is there a way to mix the two, so that I end up with a single elevation file combining both data sets correctly?

Best Answers

  • geomannie
    geomannie Global Mapper User
    Accepted Answer
    Hi Michael

    I don't usually find this a problem. Just open both files and assuming that the bathymetry has negative values and elevation positive, the profiles match reasonably well at the coastline. If the bathymetry data have positive values, use the "Alter elevation values" of the options tab of the bathymetry grid to set a scale factor of -1.

    Sometimes it helps to clip the maximum bathymetry value to zero, again under the "Alter elevation values" of the options tab, and the minimum elevation value to zero. It can also help if you export a new grid combining your 2 inputs, selecting the "interpolate to fill small gaps" option.

    I hope that this helps.

  • bmg_bob
    bmg_bob Global Mapper Programmer
    Accepted Answer

    Here is what you can do:
    1. Load both data layers into Global Mapper
    2. Open the Overlay Control Center
    3. Select your elevation grid layer and click Options...
    4. On the Elevation Options screen, click the Alter Elevation Values tab
    5. Under Valid Elevation Range, set the Minimum Valid Elevation to 0.  (It sounds like your elevation data already has values set to 0, in which case, you might need to use a very small positive number, such as 0.01 to remove the pixels with value of 0.)
    6. Click OK
    7. Select the bathymetry layer, and do the same, but set the maximum value to 0 (or very small negative).
    8. Export the result to a new elevation grid file.



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