Dear Andrea,
I have isolated some of the problematic points and tested at different
resolutions, and different smoothing parameters. The results do not seem
to be affected by any of these changes, and even when running the analysis
with only 2 points in question, the errors still occur.
Actually, you identified a bug in the function kernelbb. This bug occurs
when the smoothing parameter is much smaller than the length of the line
segment connecting two successive relocations (your smoothing parameter
sig2 is about 5m, whereas the size of the first step in your trajectory
is several thousands metres; if you try to increase the smoothing
parameter to larger values, the problem no longer occurs). This bug is
caused by a "bounding box" defined internally around each grid cell,
which is used to identify the most influential relocations (this was
used to speed up the process); the size of this bounding box depends on
the smoothing parameter (the "blank" area in your graphs is the set of
pixels for which no relocations were found in this bounding box -- which
also explains the shape of this area).
I corrected this function, and have included the correction in the new
version of the package (1.8.2). I just have uploaded this new version to
CRAN. It will probably be available on CRAN on next Monday or Tuesday.
Thanks for the bug report,
Regards,
Clément.
--
Clément CALENGE
Office national de la chasse et de la faune sauvage
Saint Benoist - 78610 Auffargis
tel. (33) 01.30.46.54.14
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