Dear all,
I'm calculating time spent per cell over a grid (study area) with the
package "trip", for satellite-tracked seabirds.
Some birds bred outside the area of interest (Kerguelen Plateau, to
design marine protected areas), so their trips didn't lie entirely in
the grid. In this case, it seems that time is added in some cells that
are not visited by the bird (tipically in the border of the grid).
This problem seems coming from pixellate(), and because I need to set
spatstat.options(checksegments=F)...
Any solution?
Many thanks
David
Here a reproducible exemple:
library(trip)
Le chargement a n?cessit? le package : sp
Le chargement a n?cessit? le package : spatstat
Le chargement a n?cessit? le package : mgcv
This is mgcv 1.7-6. For overview type 'help("mgcv-package")'.
Le chargement a n?cessit? le package : deldir
deldir 0.0-15
Please note: The process for determining duplicated points
has changed from that used in version 0.0-9 (and previously).
spatstat 1.23-4
Type ?help(spatstat)? for an overview of spatstat
?latest.news()? for news on latest version
?licence.polygons()? for licence information on polygon calculations
spatstat.options(checksegments=F) # to allow segment outside the window
# a trip with some parts outside the study area :
d <- data.frame(x = 1:10, y = c(1, 1.5, 2, 4, 5, 5.5, 8, 8, 6, 10), tms
= Sys.time() + seq(10,100, 10), id = rep(1, 10))
coordinates(d) <- ~x+y
tr <- trip(d, c("tms", "id"))
# the sutdy area :
gridaa <- expand.grid(Long=seq(-0.5, 10.5, by=1), Lat=seq(3.5, 6.5, by=1))
coordinates(gridaa) <- ~ Long + Lat
gridded(gridaa) <- T
fullgrid(gridaa) <- T
gt <- getGridTopology(gridaa)
# time spent per cell
tgrid <- tripGrid(tr, grid = gt)
image(tgrid, axes=T)
points(coordinates(tr), t="l", col="blue")
points(gridaa, pch="+")
text(x= midpoints.psp(as.psp(tr)), col="green", pos=3, labels=1:9)
sessionInfo()
R version 2.13.1 (2011-07-08)
Platform: i386-pc-mingw32/i386 (32-bit)
locale:
[1] LC_COLLATE=French_France.1252 LC_CTYPE=French_France.1252
[3] LC_MONETARY=French_France.1252 LC_NUMERIC=C
[5] LC_TIME=French_France.1252
attached base packages:
[1] stats graphics grDevices utils datasets methods base
other attached packages:
[1] trip_1.1-10 spatstat_1.23-4 deldir_0.0-15 mgcv_1.7-6
[5] sp_0.9-88
loaded via a namespace (and not attached):
[1] grid_2.13.1 lattice_0.19-30 Matrix_0.9996875-3 nlme_3.1-101
***************************************************
Dr. David PINAUD
Ing?nieur de Recherche "Analyses spatiales"
Centre d'Etudes Biologiques de Chiz? - CNRS UPR1934
79360 Villiers-en-Bois, France
poste 485
Tel: +33 (0)5.49.09.35.58
Fax: +33 (0)5.49.09.65.26
http://www.cebc.cnrs.fr/
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