Dear All, I am trying to combine various layers of data into a single image. The last layer is a sea mask to blank out some extraneous kernel areas. I have a map (read in from an ESRI shapefile using readShapePoly) as a SpatialPolygonsDataFrame, which obviously has all the countries as 'foreground', does anyone know of an easy to invert this, so the sea becomes forground? I can see in principle you might be able to do something with the RingDir slot (to turn polygons into holes and vice versa), but can't figure out how to access it to try. Any hints gratefully received! Cheers rob *** Want to know about Britain's birds? Try www.bto.org/birdfacts *** Dr Rob Robinson, Senior Population Biologist British Trust for Ornithology, The Nunnery, Thetford, Norfolk, IP24 2PU Ph: +44 (0)1842 750050 E: rob.robinson at bto.org Fx: +44 (0)1842 750030 W: http://www.bto.org eSafe scanned this email for viruses, vandals and malicious content (!) ==== "How can anyone be enlightened, when truth is so poorly lit" =====
Manipulating SpatialPolygonsDataFrames
2 messages · Rob Robinson, Roger Bivand
On Tue, 3 Apr 2007, Rob Robinson wrote:
Dear All, I am trying to combine various layers of data into a single image. The last layer is a sea mask to blank out some extraneous kernel areas. I have a map (read in from an ESRI shapefile using readShapePoly) as a SpatialPolygonsDataFrame, which obviously has all the countries as 'foreground', does anyone know of an easy to invert this, so the sea becomes forground? I can see in principle you might be able to do something with the RingDir slot (to turn polygons into holes and vice versa), but can't figure out how to access it to try.
It isn't that easy, unfortunately. You'll need not only to create an outer rectangle, but also to link up all of the internal holes so that the first fill of the mask doesn't flood the holes. That is, polygons are drawn from largest to smallest, so your initial graphic will be covered by the external mask first. Could the kernel points/rasters be overlay()ed over the land first, and then select (as say SpatialPixels) the ones to image() if falling on land? Roger
Any hints gratefully received! Cheers rob *** Want to know about Britain's birds? Try www.bto.org/birdfacts *** Dr Rob Robinson, Senior Population Biologist British Trust for Ornithology, The Nunnery, Thetford, Norfolk, IP24 2PU Ph: +44 (0)1842 750050 E: rob.robinson at bto.org Fx: +44 (0)1842 750030 W: http://www.bto.org eSafe scanned this email for viruses, vandals and malicious content (!) ==== "How can anyone be enlightened, when truth is so poorly lit" =====
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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