[GRASS-user] Landscape connectivity

[Markus Metz]

Hi Miltinho,

hmm I think the theory of Urban and Keitt (2001) practically applied to 
raster maps is what I want. But Fall et al (2007) is also very 
interesting and surely seems closer to what I'm looking for. Problem is, 
I don't have time right now to write a new module implementing these 
ideas, and want to avoid that I reinvent the wheel.
BTW, I think I found a very simple way to get my clusters in grass, just 
an idea, still have to test it.

Thanks,

Markus


Milton Cezar Ribeiro wrote:
> Hi Markus,
> So, if I understood well the practical theory you need is not that one 
> described by Urban & Keitt (2001), because they use nodes and edges, 
> and you want a patch-based graph theory, isn't it? May be Fall et all 
> (2007) is a better technical approach?
> Andrew Fall, Marie-Josee Fortin, Micheline Manseau, and DanO’Brien
> Spatial Graphs: Principles and Applications for Habitat Connectivity
> Ecosystems (2007) 10: 448–461 - DOI: 10.1007/s10021-007-9038-7
> bests
> miltinho
> brazil=toronto
>
> 2009/12/2 Markus Metz <markus.metz.giswork at googlemail.com 
> <mailto:markus.metz.giswork at googlemail.com>>
>
>     Hi all,
>
>     for a raster map with habitat patches separated by gaps in
>     between, I want to know for each habitat patch 1) how far away is
>     the nearest other habitat patch, 2) what's the id of the nearest
>     habitat patch (each contiguous patch must have a unique ID), 3)
>     how do I get to the nearest habitat patch, i.e. what is the
>     shortest path connecting one patch and its nearest other patch.
>
>     Then I need to get clusters of patches, each cluster consisting of
>     patches connected by paths not longer than max_distance, i.e. I
>     can visit all patches within a cluster by traversing gaps not
>     broader than max_distance (hop from one patch to the next, but I
>     can hop only so far...)
>
>     That would be interesting for meta-populations, dispersal etc,
>     habitats could be islands, forest fragments, trees of a particular
>     species, any habitat type with a patchy spatial distribution and
>     one or more species dependent on that habitat.
>
>     Any idea how to do that in grass or some other (fragment
>     analysis-specific) application?
>
>     Using the habitat map twice as input to r.distance would be a
>     start with r.distance maps=habitat_map,habitat_map, but r.distance
>     is too slow for my taste (running for 2 hours by now), and I still
>     have to get the nearest patches, shortest paths and clusters
>     connected with max_distance. Running r.cost or r.walk for each
>     patch as starting points and all other patches as stop points is
>     not an option because I have ~200,000 patches in a 300 million
>     cell raster. Converting the raster habitat map to a vector with
>     areas and using v.net.* modules doesn't work because AFAIK these
>     modules work with points as graph nodes, and some of the areas are
>     quite large, using centroids would give wrong distances.
>
>     The theory of what I want to do is described in Urban and Keitt
>     (2001) [1]
>
>     Thanks,
>
>     Markus M
>
>     [1] link to pdf:
>     http://www.keittlab.org/~tkeitt/papers/urban-keitt-2001.pdf
>     <http://www.keittlab.org/%7Etkeitt/papers/urban-keitt-2001.pdf>
>
>     PS: The grass module I would like to have for this kind of
>     analysis would use a habitat map as input, have as optional output
>     raster paths with distances as cell values, vector paths with
>     costs and ids of the two patches connected by each path, one
>     cluster map for each maxdistance=max1,max2,max3,..., and an ascii
>     file in the same format like r.distance for all paths connecting
>     habitat patches. X-mas is getting close ;-)
>
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