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Tool to Calculate and Additively Combine Anisotropic and Isotropic Cost Distances?

Question asked by geonetadmin on Feb 10, 2011
Original User: tnunez

I'm in search of a GIS function that will calculate cost distances, but in a specific way: I need it to calculate an anisotropic cost (from an elevation raster), and an isotropic cost (from a modeled surface of resistance to animal movement), and then I need it to additively combine these together as it accumulates cost weighted distances from the source (a polygon of animal habitat).

Spatial Analyst's PathDistance function calculates anisotropic costs, but it combines them with costs from isotropic cost calculations multiplicatively, using the formula:

Cost_distance = Surface_distance * Cost_Surface *  Vertical_factor
, where Vertical_factor = ([anisotropic change in elevation]*[Cost per
unit change in elevation])

(see http://help.arcgis.com/en/arcgisdesktop/10.0/help/index.html#/How_the_path_distance_tools_work/009z00000027000000/)

Instead, I need a function that specifically does this:

Cost_distance = Surface_distance * (Cost_Surface + Vertical_factor)

If anyone knows of a tool that does this in Arc (I'm assuming it's impossible to manually change the code for PathDistance) or one of the open source alternatives, or knows of a workaround, I would greatly appreciate it.

Many thanks,

Tristan

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