On Thu, Jul 7, 2011 at 5:25 PM, Sarah Papworth <sarah.papwort...@imperial.ac.uk> wrote: > Dear all, > > I have a jpg map of altitudinal contours in my study area which I > would like to map and use in R to calculate the altitude and slope of > GPS coordinates. > So far, I have painstakingly traced these contours in ArcMap to create > a shapefile (of polylines) with altitude. I have now imported this > file shapefile into R. > > What I would like to do is turn it into a raster of slope and > altitude, but I can't seem to find any method of doing this in the > online R help archives. Does anyone have any idea which package I > should be using, or perhaps if it is even possible to turn this type > of shapefile into a raster?
There's definitely tools for doing this in GRASS-GIS: http://linfiniti.com/2010/12/3d-visualisation-and-dem-creation-in-qgis-with-the-grass-plugin/ but not sure about R. One approach might be: load shapefile into R as a SpatialLinesDataFrame, so that each line has its height attribute. consider a grid of points over the space, and use rgeos functions to find the nearest contour line and its height. Assign height to that grid point. That will give you a grid that will look a bit like terraces between the contours, which you could possibly then smooth, although there may be systematic errors with this method... I suspect there's a better way by looking at more than one nearby contour line and doing some interpolation.... Actually the GRASS algorithms are discussed here: http://grass.osgeo.org/wiki/Contour_lines_to_DEM Barry _______________________________________________ R-sig-Geo mailing list R-sig-Geo@r-project.org https://stat.ethz.ch/mailman/listinfo/r-sig-geo