[R-sig-Geo] comparing raster and vector data with Grass/R

[Roger Bivand]

On Wed, 7 Mar 2007, Schmitt Thierry wrote:

> I am struggling to overlay spatialLinesDataFrame and
> SpatialGridDataFrame. The overlay method doesn't allow me to do so.
> 

There is no overlay method, you would need to write one, or interpolate 
points along your lines and overlay the resulting point object on the 
raster.

> As mentioned by matt, I might have a look at starspan. However, I might
> be interested to have some solution within the Grass/R interface

Could I suggest that you try v.to.rast in GRASS, and simply use multiple 
rasters? You may need care with the resolution, but in spearfish:

v.to.rast input=roads output=v_roads use=cat

then in R:

library(spgrass6)
sp <- readRAST6(c("v_roads", "elevation.dem"))
summary(sp)
sp1 <- as(sp, "SpatialPixelsDataFrame")
summary(sp1)
sp2 <- sp1[!is.na(sp1$v_roads),]
summary(sp2)
by(sp2$elevation.dem, sp2$v_roads, summary)

which just preserves the raster cells crossed by roads as defined by 
v.to.rast.

Hope this helps,

Roger

> 
> Thierry
> 
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-- 
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