I use GRASS to produce contours from DEM (r.contours for SRTM rasters). They looks fine, but most of the line features occures to be duplicated; i.e. verticies duplicated. Here are pictures of output line (first) and line with some moved vertices (second) to make my problem more clear

Original vertices

Shifted vertices

This happens to contours, which are not closed. So, they looks fine, but after generalization occure lots of artifacts, and this is unsuitable for relief visualisation.

Could somebody point out the reason of this duplication or offer a way to correct them?

  • Note: r.contours of GRASS GIS itself will not create duplications since it is a topological GIS. They must originate from somewhere else... – markusN May 15 '15 at 14:01

I'm not sure what the reason is for this duplications, but you could try running v.clean with tool=rmdupl to remove duplicates.

See also the v.clean documentation: http://grass.osgeo.org/grass70/manuals/v.clean.html

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