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Input data: 1. an SRTM raster. 2. Point file of peaks. -Attributes contain ID, x, y, z and the elevation at which the peak is completely isolated from a neighboring peak.

The output I want is a line/polygon/point/raster file containing contours for that specific elevation of peak-isolation, for all the peaks. Simply put I want to draw a contour at a particular elevation below that peak.

I have reviewed r.contour.level and r.contour.step commands in QGIS's GRASS toolbox, which can give me contours for exactly the elevations I want, but I need contours at different elevations for different peaks, as their elevation of complete isolation would be different.

I could manually do it for every peak I have, but could it be done through raster calculator for all the peaks and at specific elevations?

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    "Contour for specific coordinates" makes no sense because a contour is, by definition, an entire set of points (usually a curve) at a given elevation. Furthermore it is not possible to generate contours only from data concerning "global peaks." Could you please explain more clearly what you need, what form of input data you have, and what form the output needs to take? – whuber Feb 28 '14 at 18:17
  • Sorry for being unclear and nonsensical. Input data: 1. an SRTM raster. 2. Point file of peaks. -Attributes contain ID, x, y, elevn and the elevation at which the peak is completely isolated from a neighboring peak. The output I want is a line/polygon/point/raster file containing contours for that specific elevation of peak-isolation, for all the peaks. Simply put I want to draw a contour at a particular elevation below that peak. – csheth Feb 28 '14 at 18:53
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If you want to extract a specific elevation as contour level, then use the parameters minlevel=value and maxlevel=value of the command r.contour.

Note: r.contour.step on QGIS's processing toolbox does have min and max parameters as options.

  • I actually need contours specific to peak regions and not the entire DEM raster. QGIS's toolbox does have the min/max parameters – csheth Mar 5 '14 at 21:56
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Doing a spatial query of intersection/contains between contours_levels and Peak_points yields no result as they don't seem to be associated to each other on "canvas", but in reality they do.

This is because contours are line features and those intersect/contain only on the line, not on the area enclosed by the line. I think you would convert the contours specific to given peak to polygon areas using v.type_wrapper in GRASS (probably not available through Grass toolbox, but everytving is accessible from the commandline of the toolbox), then use the spatial query on the polygon, then convert the result back to line. Just unfinished idea for a script...

  • I am unable to find v.type_wrapper even in the GRASS plugin tool set. So I have simply selected the contours around peak regions manually. Thanks for the help anyways. – csheth Apr 3 '14 at 9:12

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