distance calculation; meuse.grid

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. 

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

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