[R-sig-Geo] overlay SpatialPolygons and SpatialGridDataFrame, overlay
e.pebesma at gmail.com
Thu Dec 24 16:59:39 CET 2009
Patrick Giraudoux wrote:
> I am trying to clip a SpatialGridDataframe using a
> SpatialPolygonsObject (actually a simple rectangle, e.g. a region),
> the ultimate aim being to extract the corresponding area to a new
> SpatialGridDataFrame corresponding to the region. I was supposing that
> I can start doing it using the overlay function. Here we are:
> I get:
> Error in WorldTemp[!is.na(idx), ] :
> (subscript) logical subscript too long
> The SpatialGridDataframe has 259200 pixels. Am I too greedy and is
> there really a limitation in length?
do first a
fullgrid(WorldTemp) = FALSE
and then do the overlay. If you want to select individual pixels, this
needs be done on SpatialPixelsDataFrame objects; if you select the way
you did it, on a SpatialGridDataFrame object, it will select grid rows,
as in WorldTemp[rowNumbers,colNumbers] -- no wonder that the pixel
indexes (cell index numbers) vector was too long.
From a design perspective, this might sound complex, but both selection
mechanisms are convenient at times, and they match the way the data are
stored. If your selection is as simple as you sketch above, you might
prefer to select straight away on grid rows and columns of a
> A second step would be to compute the upper left coordinates, etc...
> to get the new SpatialGridDataFrame But this is another story...
R does this for you automatically, by
but note that the bbox values for *Grid* and *Pixel* objects are grid
and cell corners, not cell centers.
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http://www.52north.org/geostatistics e.pebesma at wwu.de
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