calculate raster values based on vector regions

library(rgdal)
library(RSAGA)

rastermap <- readGDAL("rastermap.asc")
rsaga.esri.to.sgrd(in.grids=" rastermap.asc", out.sgrds=" rastermap.sgrd", in.path=getwd())

cellsize <- rastermap at grid@cellsize[1]
rsaga.get.usage(lib="grid_gridding", module=3)
rsaga.geoprocessor(lib="grid_gridding", module=3, param=list(GRID="polygons.sgrd",

rsaga.sgrd.to.esri(in.sgrds="polygons.sgrd", out.grids="polygons.asc", out.path=getwd(), prec=0)
rastermap$polygons <- as.factor(readGDAL("polygons.asc")$band1)

raster.polygons <- boxplot(band1 ~ polygons, rastermap at data, col=rainbow(length(levels(rastermap

str(raster.polygons)

-----Original Message-----
From: r-sig-geo-bounces at stat.math.ethz.ch [mailto:r-sig-geo-bounces at stat.math.ethz.ch] On Behalf
Of Tomislav Hengl
Sent: Wednesday, January 28, 2009 9:56 AM
To: r-sig-geo at stat.math.ethz.ch
Cc: Alexander.Herr at csiro.au
Subject: Re: [R-sig-Geo] calculate raster values based on vector regions


Dear Herry,

If I understand what you problem, one solution is to use R+SAGA. You should first convert the
polygon map to the same grid, and then you can load it to R and do any type of aggregation:

library(maptools)
library(rgdal)
library(RSAGA)

# load the gridded map:

rastermap <- readGDAL("rastermap.asc")

# load the shapefile:

rsaga.esri.to.sgrd(in.grids=" rastermap.asc", out.sgrds=" rastermap.sgrd", in.path=getwd())

# convert the polygon map to a raster map:

cellsize <- rastermap at grid@cellsize[1]
rsaga.geoprocessor(lib="grid_gridding", module=3, param=list(GRID="polygons.sgrd",

INPUT="polygons.shp", FIELD=1, LINE_TYPE=0, USER_CELL_SIZE=cellsize,
USER_X_EXTENT_MIN=rastermap at bbox[1,1]+cellsize, USER_X_EXTENT_MAX=rastermap at bbox[1,2]-cellsize,
USER_Y_EXTENT_MIN=rastermap at bbox[2,1]+cellsize, USER_Y_EXTENT_MAX=rastermap at bbox[2,2]-cellsize))

rsaga.sgrd.to.esri(in.sgrds="polygons.sgrd", out.grids="polygons.asc", out.path=getwd(), prec=0)
rastermap$polygons <- as.factor(readGDAL("polygons.asc"))

# summary statistics per polygon class:

raster.polygons <- boxplot(band1 ~ polygons, rastermap @data,

col=rainbow(length(levels(negotingrid$SOIL))))

str(raster.polygons)

You will of course need to adjust the "FIELD" position in the attribute table and the precision
"prec".

To obtain and use SAGA, check this article:
http://spatial-analyst.net/wiki/index.php?title=Software

cheers,

How is the weather now in Canberra? In Amsterdam is freezing brrr.

T. Hengl

-----Original Message-----
From: r-sig-geo-bounces at stat.math.ethz.ch [mailto:r-sig-geo-bounces at stat.math.ethz.ch] On Behalf
Of Alexander.Herr at csiro.au
Sent: Wednesday, January 28, 2009 2:10 AM
To: r-sig-geo at stat.math.ethz.ch
Subject: [R-sig-Geo] calculate raster values based on vector regions


Hi List,

How would I go about assigning values to a raster based on polygon regions in R. Examples would

be

most appreciated.

I have (vector) regions assigned to a specific value. The raster has NAs and some pixels where
these values are likely to occur on ground. I need to assign these values to the raster and can

do

this in ArcInfo through vectors and rasterizing but only to a limited raster size. And R is much
more preferable anyway...

Any help appreciated.
Cheers
Herry