distance calculation; meuse.grid
On Mon, 3 Jul 2006, Adrian Baddeley wrote:
karl.sommer at dpi.vic.gov.au writes:
I was wondering if there is a way in "R" or "sp" to calculate shortest distance from a given object such as a river, similar to the data example "meuse.grid" under the gstat package.
In package 'spatstat' there is a function distmap() designed for this purpose.
Excellent! I'll add suitable functions to the sourceforge repository spspatstat package to interface sp classes to this solution, probably within a month. The as.mask() arguments can be derived from a SpatialGrid GridTopology slot, so this will help more people. Visiting http://www.spatstat.org/ is always instructive!
The object (the river) may be either - a list of line segments (line segment pattern object, class "psp") - a list of x,y coordinate points (point pattern object, class "ppp") or - a binary pixel image (window object, class "owin", type "mask") The return value is a pixel image; the brightness value of each pixel gives the shortest distance from that pixel to the target object. You can display the pixel image, extract the values at chosen locations using the subset operator "[ ]", or extract the entire pixel array using "as.matrix". Adrian Baddeley
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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