Extraction of contour lines from a Digital Elevation Model
Select terrain model (DEM/HGT/GeoTiff)
Contour interval
Trick: Type =NN to extract contour lines for a discrete level
Output format
Output redirection

Intended usage

Adding contour lines to visualization projects done in Walls, Survex and other cave surveying software.


The converter needs a digital elevation model as input. On the output, a SVX or SRV file is produced. The file contains contour data and is essentialy ready for importing into project.

Because of limited server resources, this web service is limited to 0,5 millions of points in the contours and accepts DEMs up to 5 MB in size. Warning: Because of large size of data sets involved, the conversion may take up to a few minutes. The actual conversion is rather quick, but what may take time is transferring the input and the output over the Internet.

This program outputs UTM-projected contour data, which means the contours are oriented to topographic north. If you intend to superimpose this data with cave surveys, you should apply both magnetic decliation and grid convergence corrections to your compass readings, so that your surveys are also oriented to local UTM north and not to true or magnetic north. Things will get complicated (or inaccurate) with large caves.


  1. Obtain a DEM for your region of interest, eg. from http://viewfinderpanoramas.org. You need a HGT, DEM or GeoTiff file.
  2. If your file seems to be large (larger than 4 MB), load it into 3DEM and using Operation / Select smaller area crop it to represent only your area of true interest. Save your cropped fragment as GeoTIFF DEM
  3. Load your DEM file into the converter
  4. Click Convert
  5. Use the resulting SVX or SRV file in your Survex or Walls project