Hamish wrote: > Bob Moskovitz wrote: >> I have a 20 foot contour map shapefile that has over 47000 line strings. >> Many of these lines have gaps (see >> http://picasaweb.google.com/bobdebm/Problems/photo#5133539789447176242 ) >> in many of the contour lines. I want to use v.surf.rst to make a dem. Will >> I have problems using this file?
> v.to.rast + r.surf.contour is the usual way for creating DEMs from contour > lines. > > r.surf.contour still needs some updating from the GRASS 4 days, ie the output > is integer only and it treats 0 elevation as NULL. you can work around that by > multiplying the input map by 1000 or 10000 and then shifting 0 values up one > unit before processing and dividing by the same after. Another issue is that r.surf.contour doesn't handle disjointed contour lines well, which might be problematic for you. Also, it interpolates "flat peaks" and "lakes" if you don't supply elevation points at hilltops and depressions in the input raster. You might consider r.surf.nnbathy (with alg=nn or alg=ns) from the the GRASS AddOns WIKI - unlike r.surf.contour it handles disjointed contour lines fine, though it suffers from the latter issue as well. BTW - can anybody say if the algorithm used in r.surf.contour is the same as that described in [1] -> "ILWIS Operations" -> "Interpolation" -> "Contour interpolation" -> "Algorithm"? The authours mention: Gorte, B.G.H. and Koolhoven W., 1990. Interpolation between isolines based on the Borgefors distance transform. ITC Journal 1990-3, pp. 245-247. ITC, Enschede in the references. [1]http://52north.org/joomla/downloads/ilwis_help/ilwis.chm Maciek _______________________________________________ grass-user mailing list [email protected] http://lists.osgeo.org/mailman/listinfo/grass-user
