[R-sig-Geo] Extracting minimum convex polygons of species distributions

[Jaime Burbano Girón]

The script....

2012/3/15 Jaime Burbano Girón <jaimebg27 at gmail.com>

> Hi Louise, I have calculated minimum convex polygons with "calc_mcp"
> function from package "aspace", but I think this function is not longer
> available, so I attach my script using it, where the function is written.
>
> An other tool that I have used is the Hawth's Analysis Tools extension for
> ArcGIS: http://www.spatialecology.com/htools/tooldesc.php
>
> Cheers...
>
>
> On Thu, Mar 15, 2012 at 8:56 AM, Louise Mair <lm609 at york.ac.uk> wrote:
>
>> Hello,
>>
>> I have a distribution dataset for species consisting of xy coordinates at
>> the 1km resolution, with only presence data. So a simplified example of a
>> species distribution might be:
>>
>> y <- rbind(as.integer(rnorm(100,50,20)), as.integer(rnorm(200,100,30)),
>> as.integer(rnorm(100,180,15)))
>> x <- rbind(as.integer(rnorm(200,50,20)), as.integer(rnorm(200,100,20)),
>> as.integer(rnorm(100,200,15)))
>> plot(y~x)
>>
>> I would like to create polygons for each species distribution, where if an
>> island is present (as I have tried to show in the example), it would be a
>> seperate polygon, and the jagged edges where species distributions meet
>> coastlines etc are maintained. I have tried functions such as mcp in the
>> package adehabitat, but this produces a very coarse polygon, which doesn't
>> provide the detailed distribution edges that I need. Other functions I've
>> tried require the data already to be in the format where the only xy
>> coordinates present are the outline of the polygon.
>>
>> Can anyone please recommend a function I can use here, or suggest a way of
>> extracting the outline points? I have tried this manually but cannot seem
>> to write a code that will effectively take account of jagged edges and
>> islands.
>>
>> Thanks very much for your help,
>>
>> Louise.
>>
>>        [[alternative HTML version deleted]]
>>
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>>
>
>
>
> --
> Jaime Burbano Girón
> Maestría en Ciencias Biológicas - Ecología
> Universidad Nacional de Colombia
> Bogotá - Colombia
> (57) 3168573713
>



-- 
Jaime Burbano Girón
Maestría en Ciencias Biológicas - Ecología
Universidad Nacional de Colombia
Bogotá - Colombia
(57) 3168573713
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