On Tue, 5 Jan 2010, laure velez wrote:
Dear list member,
Although the answer to this might be straightforward I'm struggling with this
issue for weeks now :
I have a shapefile (only one polygon) and a raster (.tif). I would like to know
the value of each pixel on the raster which overlap with the polygon in the
shapefile.
I had various tries but none did work :
library(rgdal)
pol = readOGR(?shape.shp?, layer = ?shape?)
grid = readGDAL(?raster.tif?)
overlay(grid,pol)
With this I obtain ?NA? for all pixels
Could you help me ?
Please try:
image(grid, axes=TRUE)
plot(pol, add=TRUE)
If the polygon doesn't show up in the correct place, do examine summary()
output for both objects. I suspect that the coordinate values of the
objects - seem in the bounding boxes in the summary output - do not
overlap, probably because the coordinate reference systems differ.
Roger
Thanks in advance,
Laure
Please find attached the shape and the raster
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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.biv...@nhh.no
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