[R-sig-Geo] accumulate gridcells to a specific value - summary

[Alexander.Herr at csiro.au]

Hi list,

Attached code from Barry Rowling to estimate variable radii based on a given allocation value (ie matrix cell sums). The code will calculate the radii of circles that sum to a given value. It starts from the hightest value in a matrix, than second highest etc. and excludes values already allocated to a circle. The output is a matrix of circles/semi-circles and dataframe of result. See circle_allocate.r for a trial.

Cheers
Herry



-----Original Message-----
From: Matthew Perry [mailto:perrygeo at gmail.com] 
Sent: Saturday, August 02, 2008 3:12 AM
To: Herr, Alexander Herr - Herry (CSE, Gungahlin)
Cc: r-sig-geo at stat.math.ethz.ch
Subject: Re: [R-sig-Geo] accumulate gridcells to a specific value

This might be what you're looking for ...

http://grass.itc.it/grass62/manuals/html62_user/r.cost.html

On Thu, Jul 31, 2008 at 4:51 PM,  <Alexander.Herr at csiro.au> wrote:
> Hi Barry,
>
>> Can you explain a bit more about your problem?
>> * What are the inputs? Just a grid of values or are there some
> starting points?
>
> Inputs is a floating grid. Starting point is 1) the highest values in 
> the grid. Once first accumulation achieved, exclude this area and 2) 
> find highest value on grid for next starting points and so on.
>
>> * What are the outputs? A list of grid cells that add up to your
> accumulated value?
>
> outputs: accumulation areas where sum of grid points (within areas) is 
> a given value.
>
>
> Does that clarify?
> Cheers
> Herry
>
> -----Original Message-----
> From: b.rowlingson at googlemail.com [mailto:b.rowlingson at googlemail.com]
> On Behalf Of Barry Rowlingson
> Sent: Thursday, July 31, 2008 7:09 PM
> To: Herr, Alexander Herr - Herry (CSE, Gungahlin)
> Cc: r-sig-geo at stat.math.ethz.ch
> Subject: Re: [R-sig-Geo] accumulate gridcells to a specific value
>
> 2008/7/31  <Alexander.Herr at csiro.au>:
>
>> I am trying to accumulate gridcells to a specific value. This means I 
>> need to extent the nearest neighbours (or search radius) to a size so 
>> that the sum of gridcell values reaches the desired value (or stops 
>> if
>
>> sum value of gridcells/radius goes beyond a specific size). It should 
>> start with the highest gridcell value then next remaining highest etc.
>>
>> Of course this could also work with points/polygons or on a matrix.
>>
>> Rather than re-inventing the wheel I was wondering if anyone has or 
>> knows of a tool/script.
>
>  It's not totally clear what you want to do, but it sounds like the 
> sort of raster operation that GRASS GIS does.
>
>  http://grass.itc.it/
>
>  Can you explain a bit more about your problem?
>
>  * What are the inputs? Just a grid of values or are there some 
> starting points?
>  * What are the outputs? A list of grid cells that add up to your 
> accumulated value?
>
>  I ask this because this week I wrote some code that did something 
> very similar, namely:
>
>  Given a grid of resource values and a number of population centres, 
> compute the areas on the grid that allocate a given resource total to 
> each population centre by minimising the distance from each centre, 
> and not allowing any grid square to be allocated to more than one centre.
>
>  It basically grows areas out from the centres, by finding the minimum 
> centre-resource cell distance for unallocated cells and allocating 
> that cell to that centre.
>
>  This was written in Python and used gdal to read grids. Took me a day 
> to write and a day to document.
>
>  I'll have to start charging for this :)
>
> Barry
>
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>



--
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"The best way to predict the future is to invent it." -- Alan Kay Matthew T. Perry http://www.perrygeo.net


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