[R-sig-Geo] Walruses and adehabitatHR: class estUDm exclusion of non-habitat pixels and summary over all animals

[afischbach]

I am tracking a variable number of walruses throughout their summering range
in the Chukchi Sea.
We wish to summarize monthly summer foraging home ranges based on daily
locations and a daily summary of foraging behavior measured by instruments
on-board the satellite-linked tag, which is a metric similar in nature to
the 'activity' index utilized by Benhamou and Cornelis (2010).

For each walrus with a threshold amount of tracking in each month I
construct a utilization distribution.  Then I must exclude land as
non-habitat from each walruses monthly utilization distribution.  
Because their summering range abuts a coastline that is too complex (sharp
peninsulas and sounds that violate the angle rules and relatively short
shore line segments that violate the 3*h rule of Benhamou and Cornelis
(2010)) the BRB(boundary=simpleCoastLine) option fails.  As such, I am
inclined to resort to the raster exclusion approach, whereby a
pre-constructed raster with cell values assigned to 1 (habitat) or 0
(non-habitat) is multiplied against each utilization distribution, all built
on the same raster grid.

Under the predecessor package, adehabitat, I would multiply each estimated
utilization distribution (class asc) by a raster (also of class asc, read in
using the rgdal readGDAL() function).

Please advise on  how to multiply out the non-habitat from the estUDm class
object and how to normalize total volume back to 1.

Also, please advise on how to summarize utilization distributions across
walruses (in each estUDm object) to derive a single generalized utilization
distribution for each month.


-----
Tony Fischbach, Wildlife Biologist
Walrus Research Program
Alaska Science Center
U.S. Geological Survey
4210 University Drive
Anchorage, AK 99508-4650

AFischbach at usgs.gov
http://alaska.usgs.gov/science/biology/walrus
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