shortest realistic distance for fish travel

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.

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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