[GRASS-user] Re: grass-user Digest, Vol 46, Issue 63

[Richard Chirgwin]

Gary,
> Message: 2
> Date: Mon, 22 Feb 2010 05:00:09 -0800 (PST)
> From: Gary Nobles <garynobles at yahoo.com>
> Subject: [GRASS-user] Re: calculating maximum and minimum diameters
> 	with, GRASS or R and GRASS?
> To: grass-user at lists.osgeo.org
> Message-ID: <1266843609307-4611842.post at n2.nabble.com>
> Content-Type: text/plain; charset=us-ascii
>
>
> Is there no simpler way? e.g using the centroid as a center spot and then
> find the part of the polygon which is furthest away and use that distance
> for max radius? (and min dist for min radius)
>
> or make grass create a circle increasing in size untill it is fully outside
> the polygon then use that radius?
>
> Is this beyond GRASS? There must be a way using R - although I am still
> learning so I would be greatful of any instructions of how to do this in R
> (including which libraries to use) I may have to go to a R forum, any good
> ones?
>   

There are a few approaches that occur to me. One thing I think you'll 
need is a map showing just the centroid locations (as points). You can 
do this by using v.extract, eg:

v.extract <input map> output=<output map> type=centroid

Then you could use v.distance measure distance from the centroids to all 
the boundaries in the original map, capture this in a database table, 
and select the min and max associated with each centroid.

A question for others in the list: if you use the -a flag in v.distance, 
from centroid to line, I presume the measurement from the centroid is to 
all nodes on the line?

Richard