[R-sig-Geo] shortest realistic distance for fish travel

[van Etten, Jacob (IRRI)]

You could also look at "resistance distance" (open-source software available at http://www.circuitscape.org/) if your fish travel as random-walkers.

Jacob van Etten

-----Original Message-----
From: r-sig-geo-bounces at stat.math.ethz.ch on behalf of Alisa Coffin
Sent: Fri 19/12/2008 04:16
To: Jon Loehrke
Cc: r-sig-geo at stat.math.ethz.ch
Subject: Re: [R-sig-Geo] shortest realistic distance for fish travel
 
Jon,

You could tackle it using a raster-based least-cost path analysis as was
suggested. For that you will need a data layer at the appropriate resolution
to serve as a cost surface. I would expect it to contain at least
bathymetry, but possibly other variables as well, depending on what the
critter considers a more or less costly way to move (e.g. seagrass density,
currents, etc.).

If you had a network of origins and destinations, you could approach it as a
shortest-path network problem. The only R module I'm familiar with for
network analysis is igraph, which I have used to calculate the shortest
(topological) path from point 1 to point 2 within a network graph.

Alisa.

On Thu, Dec 18, 2008 at 2:38 PM, Jon Loehrke <jloehrke at umassd.edu> wrote:

> Hi,
>
>        I am trying to find an algorithm or thoughts on approach for how to
> compute the shortest realistic distance between two points.  I define
> shortest realistic distance as the shortest distance between two points that
> a fish (which is what I study) could move through.  Hence the path must wrap
> around land, islands, archipelagos, etc.
>
> Point 1
>
> 41.15   N
> 71.26   W
>
> Point 2
>
> 42.17   N
> 70.37   W
>
>        I'm sure this issue has come up with the geo-statistical community,
> but simply need a starting direction.
>
> Thank much and happy holidays.
>
> Jon Loehrke
> Graduate Research Assistant
> Department of Fisheries Oceanography
> School for Marine Science and Technology
> University of Massachusetts
> 200 Mill Road, Suite 325
> Fairhaven, MA 02719
> jloehrke at umassd.edu
> T 508-910-6393
> F 508-910-6396
>
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>
>


-- 
Alisa Coffin, PhD. Candidate
Department of Geography
University of Florida
Gainesville, FL  32611

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