Global Mapper Pro

How do you create a custom shader based on a relative elevation.

I want to pick a design elevation, ie 2010 and then develop a shader that will shade display increments such as -10, -8, -6 ...0,2,4,6,8, 10 feet below and above that set elevation.  I want the display to shown -10  .....10 and not real elevation. I am not sure that is possible without adjusting the whole DEM down by 2010 feet to get that value to now be the 0.  Thanks


  • Hi WetlandGuy,

    The GM Custom Shaders are highly flexible, but I don't know of a way to do what you are asking without shifting the DEM.  

    A possible "cheat" might be to shift the DEM just once so you can create your Elevation Legend from -10' to +10' and save it/screen clip it as a jpeg. Then shift your DEM back to datum to do your work and apply your 2000' to 2020' shader and when creating figures via the Map Layout Editor instead of inserting the "Elevation Legend Element" insert your Cheat legend as an Image Element. I've done this before and nobody was any the wiser. 

  • bmg_bob
    bmg_bob Global Mapper Programmer
    edited August 2021

    It sounds like you need to change the way that the elevation legend displays values so that it displays a central elevation (2010, in your example), and several increments above and below that value (-10 to +10). I don't think you need a new type of shader, per se, to accomplish this as long as your shader uses an appropriate increment (2 in your example) so that you get the colors you want. This would require new function in the elevation legend, though.

    Is this what you are looking for?

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