The following R example might be a bit off-topic, but it does show how
to create a point grid
and then use it to extract samples from an underlying set of vector
polygons. The vector polygon
data could probably be replaced by a raster grid. Though not a very big
one, given R's memory
limitations.
http://www.nceas.ucsb.edu/scicomp/GISSeminar/UseCases/SampleVectorPolygonsRasterGrid/SampleVectorPolysRastGrid.html
I might suggest the use of GRASS for this task.
Rick Reeves
Dylan Beaudette wrote:
On Wednesday 10 December 2008, Rob Robinson wrote:
Help - please! :-)
I have what I thought was a really simple problem. I have a raster image
of satellite data from which I would like to extract an arbitrary (but
simple rectangular) portion for subsequent analysis (which I'll need to do
for many images). I have the data as a (projected) SpatialGridDataFrame and
have tried two approaches: create a SpatialPolygon and overlay it (but I
don't think overlay does what I would like it to do), or access the coords
slot of the data set and pick those within the range. I haven't been able
to get either to work - presumably because my R is not good enough! It
seems a fairly common task, but I haven't yet stumbled across an FAQ or
page in ASDAR which seems to help. Any pointers anyone?
Many thanks for any help
Cheers
rob
Not sure how to do this in R, but gdal_translate can do this for you on the
command line. you will need a working GDAL install.
Cheers,
Dylan
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