Dear list, I have been given a set of ASCII grids which I read into R using readAsciiGrid(). The grids represent an interpolated water depth data set for a set of lakes; each grid represents a separate lake. For some reason I have been asked to convert this gridded data into a set of polygons. For example; given the gridded data, I want to generate a polygon that covers the area of the lake (from the grid) that is 1-2m deep say. I would then need to write out this polygon as an ESRI shape file.
Are there tools in R to do this sort of conversion? It is a bit more complex that the simple example, as lakes can have multiple basins (areas of deeper water). Say a lake has two deep areas so a cross section through the lakes might look like a W, for such a lake I would require an object that contained two polygons representing the area of the lake between 4 and 5 meters say in *each* of the basins. These would then be read out into a shape file. My GIS colleague indicates that ArcGIS/ArcMAP has a function to polygonise a raster grid in such a way. Is there something similar in the R spatial software stack? An alternative approach would be to contour (at appropriate depth intervals) the interpolated grid and convert the set of contours into polygons for individual lakes. Is there a function to do this? As you can see, this is very much a look-see at the moment. We are evaluating whether it would be quicker to work out how to do this in R as opposed to doing it by hand in ArcGIS. Any suggestions would be most gratefully received indeed! All the best, Gavin -- %~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~% Dr. Gavin Simpson [t] +44 (0)20 7679 0522 ECRC, UCL Geography, [f] +44 (0)20 7679 0565 Pearson Building, [e] gavin.simpsonATNOSPAMucl.ac.uk Gower Street, London [w] http://www.ucl.ac.uk/~ucfagls/ UK. WC1E 6BT. [w] http://www.freshwaters.org.uk %~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~%~% _______________________________________________ R-sig-Geo mailing list R-sig-Geo@stat.math.ethz.ch https://stat.ethz.ch/mailman/listinfo/r-sig-geo
