[R-sig-Geo] distance calculation; meuse.grid

[Roger Bivand]

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