Global Mapper v24.1

Prevent unwanted fill/shading on areas with no data on a dem

NEV Global Mapper UserTrusted User
On a bathymetric dem - either loaded directly or as a created elevation grid from xyz data or contours, how do I prevent unwanted lines drawn across the land area as shown on attached? Conversely, how do I prevent a dem with terrestrial data from drawing across the bay - also attached.


  • TaylorD
    Answer ✓

    You can  do two things:
    1. When generating the Grid you can specify the Elevation Grid "No Data" Distance Criteria, which will determine how far GM will draw a TIN between data points (ex. you have a 5ftx5ft data set, you change the "No Grid" setting to ~5-6ft and it will only TIN to points within that distance). This works  most of the time but you have to be aware of any large gaps in your datasets and adjust the "No Data" slider accordingly.

    2. If you don't do  step one, you can check the Save TIN as Vector Layer box. When the Grid/Raster is generated, a TIN will also be generated. From there you use Advanced Selection Options>Poly Select to manually select and delete unwanted triangles within the generated TIN.  Once you have removed unwanted triangles, you generate another Grid off of the recently edited TIN, and the new Grid will only be trimmed down to your edited tin.

  • kfroese
    kfroese Geotechnical Engineer Trusted User
    Answer ✓
    3. Use an area to crop the DEM when exporting. I have sometimes wrapped a bounding box around the raw point data, generated the terrain surface, then used the bounding box when exporting to GMG to crop the data. Then opening the GMG gives me both the speed of that format and a clean edge.