Create a shoreline mask

Eric GEric G Global Mapper UserPosts: 26
edited April 2009 in Technical Support
Hello. I would like to know if it is possible to use vector shoreline data as a mask to clearly define the shoreline between bathymetry and topography for which I use colour-coded levels?

I want to use the vector shorelines as limit with on one side the colour-coded water and on the other, the land, but the shore limit isn't usually well defined in raster data (SRTM3 vs SWBD, SRTM30 Plus vs GSHHS or WDBII, etc.), so making my topographic maps is a bit problematic.

Until now I used to export first the raster bathymetry with the positive elevations using the same colour as the upper bathymetric level, exporting then the topography with negative elevations using the first colour of the land, and finally using the vector data to create a mask in a raster edition software, compiling each of them as layers to get a final 'clean' raster background map which I complete with the vector (as SVG) data.

Making this when representing only positive elevations is pretty easy, using the shoreline with the water as an area, but I would like to know if there's a one-step way to do this distinction water/land with both representations directly from GM?

Thanks for your answers.

Comments

  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited April 2009
    If you have the vector shoreline as area features, you could simply select those land areas, then export a new elevation format file using those as a crop area to get just the elevations from loaded layers in those areas, then overlay the result on the underlying bathymetry.

    Another approach would be to mark any 0 elevation areas as invalid in the bathymetry data on the Adjust Elevations tab of the Options dialog for that layer, then just make sure it is on top of the land elevation. Then the land elevation data will only show through where the bathymetry has an elevation of 0.

    Let me know if I can be of further assistance.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
  • Eric GEric G Global Mapper User Posts: 26
    edited April 2009
    Thanks Mike.

    I didn't pay attention until now to this interesting export option “Crop to selected area features” which resolves my problem. There are so many features in this software that I see I've still to learn a lot about it.

    But wow! The operation takes a lot of time for a couple CleanTOPO2/WCL (self-created as areas) for the whole world.

    Have a good day.
  • global_mapperglobal_mapper Administrator Posts: 17,238
    edited April 2009
    Cropping can be very slow if you are cropping to a polygon with a lot of vertices (the time increases non-linearly with more vertices). If you can export your crop polygon to a Global Mapper Package file and simplify it then you should get a faster export with a slightly less detailed crop.

    Thanks,

    Mike
    Global Mapper Support
    support@globalmapper.com
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