[R-sig-Geo] R, raster & SAGA

[Andy Wilson]

Hi all,
I'm new to R (and SAGA) and hope you can help resolve a problem which is 
perplexing me. As part of my project i would like to use the 
ta_morphometry module in the RSAGA library to calculate curvatures for a 
DEM. I've cut back my code to the basics below: read the DEM, write this 
into a SAGA format (I think I need to do this to make use of the SAGA 
functions), call the RSAGA function which outputs the data in SAGA 
format and finally read that data file (curve.sdat) into a raster 
object. It seems to work (no errors thrown), but when I try to do 
anything with the curve raster (including just plot it) I get the error 
message "Error in endrow - nrow : non-numeric argument to binary operator".

This all works fine within the SAGA GUI, including plotting the curve 
data, but I still cant read the output data file into R using raster. 
Instead I have to export from SAGA as another format (eg Surfer) in 
order to be able to read the data into a raster object. However I'd like 
to be able to script the process without resorting to using the GUI to 
change the file format.

Many thanks for your advice,
Andy Wilson

library (rgdal)
library (RSAGA)
library(raster)

r_elev <- raster("C:/Dissertation/DEMs/DEM.IMG")

#set environment for SAGA
myenv <- rsaga.env(workspace="C:/Dissertation/SAGA")
#output the DEM raster into a SAGA readable format
writeRaster(r_elev, filename="C:/Dissertation/SAGA/elev.sgrd", 
format="SAGA", overwrite=TRUE)
# call the module function using geoprocessor
rsaga.geoprocessor("ta_morphometry", 0, 
list(ELEVATION="elev.sgrd",SLOPE="slope",ASPECT="aspect", 
CURV="curve",METHOD=5),env=myenv)
#create a raster from the curve data file
r_curve <- raster("C:/Dissertation/SAGA/curve.sgrd")
#plot the curve data
plot(r_curve)