[GRASS-user] r.neighbors - annulus (torus) neighbor

[Glynn Clements]

Jasiewicz Jarosław wrote:

> while I need annulus (or torus) neighbor to some of my work I added 
> easily it to neighbors (grass 65 delev) module. Because I do not won't 
> to create a fork of that module I put it on that url:

If you need neighbourhood shape other than a square or circle, use the
weights= option.

Masks can be created using NumPy; e.g.

	from numpy import *
	r = 7		# outer radius
	r0 = 3		# inner radius
	d = sqrt(fromfunction(lambda x, y: (x-r)**2 + (y-r)**2, (2*r+1, 2*r+1)))
	m = logical_and(d >= r0, d <= r)
	savetxt('weights', m, fmt = '%d')

Or for smooth edges:

	from numpy import *
	r = 7		# outer radius
	r0 = 3		# inner radius
	d = sqrt(fromfunction(lambda x, y: (x-r)**2 + (y-r)**2, (2*r+1, 2*r+1)))
	m = minimum(1, maximum(0, (r-r0)/2 - abs(d - (r+r0)/2)))
	savetxt('weights', m, fmt = '% .3f')

If you only need a mask (weights of 0 or 1), you can use anything
which can outupt PGM files (use the P2 "text" format and cut off the
header).

-- 
Glynn Clements <glynn at gclements.plus.com>