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I have two shape files containing height information of a certain area and I need to create a raster DEM with GRASS using them.

  • file 1 consists of height information in contours (isolines)
  • file 2 consists of height information with spot heights

What would be the best technique to generate raster DEM with these two types of data?

Do i need to generate some spot heights from contours and then integerate with existing spot heights for DEM generation or any other method?

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    What is the density of the spot elevations? – Jay Laura Jan 12 '13 at 18:07
  • No regular density as such (almost irregular-random) – Sanjeewa Jan 13 '13 at 6:33
  • Consider altering the title of this qestion to be more precise as to what is the source data from which to generate a DEM. – Nikos Alexandris Nov 11 '13 at 13:54
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I would highly recommend going through the Contour lines to DEM tutorial, available from GRASS wiki. Essentially, they describe different interpolation methods used to produce a DEM. Avoid IDW interpolation using contour lines (i.e. described in one segment of the tutorial) since this is an inappropriate use of the interpolation method. The GRASS module r.surf.contour is probably what you are looking for--more details about the module available here. Their tutorial shows a pretty good interpolated DEM from rasterized contour lines:

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    As an analysis step you could then compare the contours to the spot elevations to start to develop an error metric. – Jay Laura Jan 12 '13 at 18:07
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    @Jay That would be a good approach when the spot elevations are randomly selected or even when they are obtained on a regular grid. Since most spot elevations, though, are usually chosen at very special points--such as mountain peaks--an analysis of their discrepancies with respect to any DEM would give a highly misleading sense of the DEM's accuracy. – whuber Jul 28 '14 at 18:33
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The OP's question was to generate a DEM from contour lines and spot elevations. I do not think that this is possible using QGIS or GRASS. The r.surf.contour module works OK for converting contour lines into a DEM, but you cannot include spot elevations.

From the GRASS manual: r.surf.contour only works if "there are no disjointed contour lines, and no spot elevation data BETWEEN contour lines exist".

The manual claims that r.surf.contour will work for "Spot elevations at the tops of hills and the bottoms of depressions", but I have been unable to make it work with even a single spot elevation added to a hilltop or depression.

As far as I have found, the only solution to generating a DEM from spot elevations and contours is using the ESRI product Topo to Raster.

If anyone is aware of a QGIS or GRASS solution to this question, that would be great.

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