Dear list members,
I am trying to implement a toroidal correction in a 10x10 matrix (meaning
that for example cells on the left edge are direct neighbors to cells on the
right edge). I wanted to achieve this by recalculating the distances in a
neighborhood matrix created with find.neighbor() from module(spatial). I
first recalculated the distances as they should be in the neighborhood
matrix and found a surprising deviation. For example the cell pair with
coordinates (1,1) and (10,10) should have a Euclidean distance of
> sqrt(2*9^2)
[1] 12.72792
However, in the matrix created by find.neighbor() the corresponding distance
is:
> x12.nhbr[1,3]
[1] 12.75879
Can anyone enlighten me why the numbers differ? The find.neighbor function
calls on a C routine for finding the distances, so I cannot look at the code
directly.
I'm using Splus 6.1 for Windows on a Windows XP pro computer.
Thanks
Volker
_______________________________
Volker Bahn
Dept. of Wildlife Ecology - Rm. 210
University of Maine
5755 Nutting Hall
Orono, Maine
04469-5755, USA
Tel. (207) 581 2799
Fax: (207) 581 2858
volker.bahn@umit.maine.edu
http://www.wle.umaine.edu/used_text%20files/Volker%20Bahn/home.htm
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