[R-sig-Geo] Step characteristics on raster maps

[Mathieu Basille]

Dear list members,

I'm trying to compute characteristics along steps (i.e. segments between 
two points), based on underlying raster maps. The steps originally come 
from radiotracking data, converted to ltraj objects (adehabitat). The 
idea is to compute (for example) the habitat composition corresponding 
to each step instead of each points, as we are interesting in the 
movement path.

I tried different solutions, as I would like to do it with R. I did not 
find any solution using adehabitat (or the development versions 
adehabitatMA/LS); 'join' only works for point characteristics, not 
steps. I also tried using sp and SpatialLinesDataFrame, but overlay does 
not seem to work with SpatialLines(DataFrame) and SpatialPixelsDataFrame:

Error in function (classes, fdef, mtable)  :
   unable to find an inherited method for function "overlay", for 
signature "SpatialPixelsDataFrame", "SpatialLinesDataFrame"

I also investigated packages raster, trip, and rgeos, without success. 
Maybe the low level functions of rgeos could be used, but it seems a bit 
out of my skills (and time available) at the moment.

Another solution might be to use spgrass6 in conjunction with GRASS, but 
I'm not familiar enough with GRASS to judge if it is a viable alternative...

I'd welcome any hints/thoughts on this question.
Sincerely,
Mathieu Basille.


-- 

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Mathieu Basille, Post-Doc

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Laboratoire d'Écologie Comportementale et de Conservation de la Faune
+ Centre d'Étude de la Forêt
Département de Biologie
Université Laval, Québec

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http://ase-research.org/basille

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``If you can't win by reason, go for volume.''
Calvin, by Bill Watterson.