You could try the focalFilter function in the raster package: install.packages("raster", repos="http://R-Forge.R-project.org")
with this argument for the Sobel filter: filter=matrix(c(1,2,1,0,0,0,-1,-2,-1) / 4, nrow=3) (For using raster this way you should upgrade to R 2.9 first, if you have not done so yet; otherwise you will get an old version; this is an unpleasant feature of R-forge) Robert On Wed, May 6, 2009 at 11:15 AM, Tim Sippel <tsip...@gmail.com> wrote: > I'm looking to calculate gradients from oceanographic variables (ie. sea > surface temperature, chlorophyll, etc.) for which I have downloaded in ESRI > grid format (.asc). From some research on gradient analysis, I have found a > few people who have used a Sobel filter to estimate gradients in images (ie. > presumably .tif or similar files). However, I have tons of data in ESRI > grid format, and all of it is unprojected (ie. lat/lon coordinates). I'd > appreciate suggestions on this if anyone has ideas. One of the primary > issues to overcome is that the units of my grids are different (ie. > x=longitude, y=latitude, z=temperature) and my grid files span the entire > south Pacific Ocean. > > Thanks, > > Tim > > [[alternative HTML version deleted]] > > _______________________________________________ > R-sig-Geo mailing list > R-sig-Geo@stat.math.ethz.ch > https://stat.ethz.ch/mailman/listinfo/r-sig-geo > _______________________________________________ R-sig-Geo mailing list R-sig-Geo@stat.math.ethz.ch https://stat.ethz.ch/mailman/listinfo/r-sig-geo