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

Jarek Jasiewicz jarekj at amu.edu.pl
Mon Nov 15 10:57:55 EST 2010

```Glynn Clements pisze:
> 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