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

Roger Bivand Roger.Bivand at nhh.no
Wed Mar 7 21:33:43 CET 2007

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 

> 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:

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

which just preserves the raster cells crossed by roads as defined by 

Hope this helps,


> 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

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