OSM Tools
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DEM File structure

We know a lot about the pointers and variables in a DEM subfile (check this WIKI) , but not about the actual hill shading bit located in DEM2.

For additional findings see pdf Exploring DEM.

How to Incorporate DEM subfiles into your IMG to create a gmapsupp.img

DEM Files operate independently of other subfiles.

As long as

  • the FID and PID in all your subfiles are the same
  • the area of your img is larger than that of the DEM
  • there are at least 4 zoom levels in your main IMG

You can attach your DEM subfile to the end of your IMG eventhough some of the blocks provide unexpected results.

  • Create an IMG using say mkgmap with name: 12345678.img.
  • Use TYPWiz to give your map colour and create a TYP file.
  • Load TOPO IMG covering the same area into GMaptool ,use the Split option and select subfiles. Click Split All
  • Rename DEM subfile as 12345678.dem
  • Add both 12345678.IMG and 12345678.DEM file to Gmaptool
  • Use Join option & tick set mapset FID; enter say FID:4664 PID:1
  • Next to Output File: give the path and name of detination file , ie c:\87654321.img
  • Click Join All
  • Check existence of this new file
  • Import this file and TYP file into Mapsource using MapsetToolkit
  • When exporting to your gps you may have to enable a 'Shaded Relief" option.
Adding a DEM look to your IMGs    

Yes, it is possible to convert readily available DEM data yourself and add it to your IMGs using the 'Polygon' method with some pleasing results:

This mapset was created using osm data and DEM data converted to an .mp file.

The TYP file includes polygons for hights 50 - 400m with 25m intervals.


  • download .hgt file
  • convert to geo text using Landserf
  • convert to .mp file
  • add mp file to osm data in Mapuploader4
DEM Investigator    
A GUI that illustrates base heights for each tile ; you can alter data found in DEM1 DEM2 and DEM3