Global Mapper v25.0

Combine/Compare Terrain

rreed
rreed Global Mapper UserTrusted User
edited May 2014 in Technical Support
Hello,

I have a simple question. In the Combine Terrain Options dialogue, if I'm subracting two surfaces, is the "First Elevation Layer" the base layer, and the second elevation layer the one that is sbutracted from the frist? It seems so, but I want to be absolutely sure I understand what GM is doing.

Also, I don't see a Help topic/definition for the "Compare Value (if Applicable):" field. What does this do?

Thanks.

Russ

Comments

  • global_mapper
    global_mapper Administrator
    edited February 2014
    Russ,

    Yes that is correct, the 2nd layer is subtracted from the first.

    The 'Compare Value' is only used for those compare/combine types where it's something like 'Keep First if Second > Value'. Then you have to define the value you are comparing to.

    You might also be interested in the Raster Calculator under the Analysis menu for applying more complex formulas to terrain layers if the built-in ones on the Combine/Compare Terrains option don't do what you need.

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Guru
    geohelp@bluemarblegeo.com
    Blue Marble Geographics for Coordinate Conversion, Image Reprojection and Vector Translation
  • JSL
    JSL Global Mapper User Trusted User
    edited May 2014
    Mike, is it possible to combine more than two layers at a time? I've got a global terrestrial/bathymetric DEM that I want to combine with 3 higher resolution terrestrial DEMs. Do I just have to combine two DEMs, then keep combining that combination with the other DEMs, or is there a way to do all four layers at once? The 3 higher res DEMs are all in different areas, so they don't overlap with each other, just with the global DEM.

    Thanks for your help.
  • global_mapper
    global_mapper Administrator
    edited May 2014
    Some Compare/Combine Terrain operations allow combining multiple layers in the latest GM versions, including addition, max, min, and average. Just those operations that require 2 layers, like subtraction or division, can only do 2.

    If you just want to use the higher resolution data wherever available simply load the lower resolution terrain first, then load the higher resolutions in order and you should automatically get the higher resolution where available and the lower resolution underneath showing through otherwise. You can then just export those all to a single new image at the desired resolution to combine them in that order.

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Guru
    geohelp@bluemarblegeo.com
    Blue Marble Geographics for Coordinate Conversion, Image Reprojection and Vector Translation
  • JSL
    JSL Global Mapper User Trusted User
    edited May 2014
    Thanks for that information, Mike. When you say to export them as a single new image at the desired resolution, do you mean export them as a workspace? Or as a raster or vector? And what parameter decides the resolution? For example, when I export something as a kml, there's no option for resolution.

    Thanks for the help.