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I have DWG file that contains couple of layers, among others I have "elevations" layer (that consists of only 80 points) and "contours" layer that can be seen on the images below. My goal is to make DEM from any resource that would be suitable to accomplish this task.

In the above image you can see Elevations + borders layer, and in the below one can see Elevations + contours + borders layer.

Elevations + borders layer Elevations + contours + borders layer

I don't have any CAD installed so I am using online software to read file and also to convert it to dxf. When I converted file to dxf and opened it in QGIS I could only see elevations of points but not contours in attribute table (I assume that even this bigger black elevation on the image above 91.00 is missing). Any kind of interpolation that I was doing in QGIS (How can I create a DEM from Point Data) didn't gave me result which would be similar to the contours that I already have in dwg file. I was also trying to do something in Surfer v.8 at first and I wasnt satisfied with result at all, and in Surfer v.13 I was given a notice that I have inssuficients number of points. I guess the real problem is that I have really only 80 points that dont represent good enough terrain but maybe I am wrong. Then I am wondering how did the dwg file creators made contour lines.

Should I continue searching for solution to this problem or should I start searching how to join elevation attributes to the contour layers (by calculating them manually or any other approach that anybody suggest) and try to make DEM from it?

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  • You can't construct a Digital Elevation Model without elevation data. You could assign values to contours from a sparse set of points, but the odds are that there will be significant errors. – Vince Apr 7 '17 at 12:41
  • I have elevation data of points (which by my opinion dont represent terrain very well)! But I dont see that contour lines have elevations so I assume that contours were made with some plugin. – newbie_girl Apr 7 '17 at 12:48
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    If the contours are lines with no height attribute you are stuck, there's no way of telling if they are going up or down, for example. You need to get the height attribute of the contours, if possible, or you can't do anything. – Spacedman Apr 7 '17 at 13:30
  • Do each of the contour lines have an available value for elevation to them? And are they separate features? If you have QGIS installed you should also have the gdal tools installed which might give you something to work with. Extract each value, rasterize, and then merge? – Alec Bennett Apr 9 '17 at 4:16

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