Slope and Aspect calculations in R
On Thu, 9 Jul 2009, Josh London wrote:
Thanks for the suggestions so far regarding the use of GRASS or SAGA. We have considered those options but SAGA doesn't appear available for MacOS. My understanding is that spgrass6 is more for accessing R code/functions from within GRASS vs accessing GRASS functions from within R. We have all our other analysis coded up in R, and just need these functions to do one part of a bigger process. Maybe I'm misunderstanding how to use R and GRASS together. I'll do some further research.
From 0.6-* on CRAN, you can create an anonymous GRASS location on the fly
with initGRASS() and run GRASS commands like r.slope.aspect with execGRASS() from the R side. See http://www.geomorphometry.org/R.asp for some examples - foot of page. You may also want to look at the underlying literature, and some of the functionality being provided in the raster package on R-Forge. Roger
Thanks again Josh Josh London wrote:
Hello We are looking to mimic, in R, the slope (max magnitude difference between a cell and its neighbors) and aspect (direction of maximum magnitude difference) functions found in ESRI's Spatial Analyst package. We were just about to code up the slope function but thought I would make sure we weren't re-inventing any wheels already out there. Thanks Josh
Roger Bivand Economic Geography Section, Department of Economics, Norwegian School of Economics and Business Administration, Helleveien 30, N-5045 Bergen, Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43 e-mail: Roger.Bivand at nhh.no