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

>

> _______________________________________________

> R-sig-Geo mailing list

> R-sig-Geo at stat.math.ethz.ch

>

https://stat.ethz.ch/mailman/listinfo/r-sig-geo>

>

--

Alisa Coffin, PhD. Candidate

Department of Geography

University of Florida

Gainesville, FL 32611

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