[GRASS-user] raster area problem

[Michael Barton]

Jason,

To do this, you need to implement some grass commands in a script that
iterates. We¹ve done something similar for the Mediterranean Landscape
Dynamics project. Our script ³grows² an agricultural catchment that meets
certain criteria (slope below some cutoff and minimizing travel costs to the
fields) until it reaches a certain number of hectares (i.e., number of
cells).

We iterate over a cost surface. You could do the same. Alternatively, you
could start with a small circular mask and increment it with r.grow. At each
iteration, you can parse r.info to calculate the number of cultivatable
cells. When you reached the desired size, you stop the loop and turn your
mask into a raster catchment.

Michael
__________________________________________
Michael Barton, Professor of Anthropology
School of Human Evolution & Social Change
Center for Social Dynamics & Complexity
Arizona State University

phone: 480-965-6213
fax: 480-965-7671
www: http://www.public.asu.edu/~cmbarton




From: Jason Jorgenson <jjorgenson at gmail.com>
Date: Wed, 1 Nov 2006 13:17:14 +0000
To: <grassuser at grass.itc.it>
Subject: [GRASS-user] raster area problem

Hi all.  This is my first attempt at using the mailing list...

I have digitized a topo map's landuse classes into a vector layer, and then
converted the vector to a raster.  I want to see how much land would have
been required for settlements at point x,y with population of 'P' to sustain
themselves.  Example, for site 'Shuna'  with a population of 5000 I need 16
sq km (of landuse classes 1,2,5 (agricultural,olive,fruit)).
http://arkygeek.blogspot.com <http://arkygeek.blogspot.com/>   for a crude
drawing of what i mean...

 What I am trying to do is (ultimately) determine the radius of the circle
that will contain 'A' square meters of usable land.  These are the general
steps I have come up with...

1.  the landuse classification data
       - convert the vector layer of classified land to a raster.
           
2. this new raster will contain 2 values - 0=not usable and 1=usable
(??should i do this??) and then I can do this
     - ask for population size of settlement
     - ask for site to analyze which will give xy
     - ask for ratio of crop:fallow  (any other variables can be set here as
well) 
     - computer determines amount of land required to sustain population
     - calculate the radius of a circle surrounding site that encompasses
the required amount of land

3. The logic for calculating the radius looks like this: (??????)
    
    for every locality do
       set solution found flag to false
            while solution not found
                 increment proposed radius
                 select all cells within proposed radius
                 test if solution is found

4. Once the radius is found, mask the results, convert the results to a
vector, and this should give me the solution. (???????)

Any suggestions???

Thanks for your time!



-- 
Jason Jorgenson
Post Grad Research Student
University of Liverpool

"If you don't get out of the box you've been raised in, you won't understand
how much bigger the world is." - Angelina Jolie

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