[R-sig-Geo] How to calculate time spent on a world grid with circumpolar trips

[Pinaud David]

Dear all,
I want to calculate a grid of time spent per cell with albatross data. 
The goal is then to relate this to fisheries data set on a 1x1° grid.
I use the trip package with tripGrid(), but have some problems with 
birds crossing the date line.
Usually I use a projection to do that but here I need to keep the 1x1° 
grid in order to relate density tu some data (fisheries...).
I've tried with recenter() and nowrapSpatialLines(), without success.
Here a code:

library(trip)
library(maps)   # to draw world maps

d <- data.frame(x=c(seq(50, 180, 10), seq(-170, 50, 10)), y=rnorm(n=37, 
m=-50, sd=3), tms=Sys.time()-(37:1*60*60*24), id=rep(1, 37))  # an example
coordinates(d) <- ~x+y
tr <- trip(d, c("tms", "id"))
proj4string(at) <- CRS("+proj=longlat +ellps=WGS84")

map('world')
plot(tr, add=T)
points(coordinates(tr), t="l")

# grid
grid.base <- expand.grid(Long=seq(-180, 180, by=1), Lat=seq(-70, -15, 
by=1))   # tab coords
coordinates(grid.base) <- ~ Long + Lat
proj4string(grid.base) <- CRS("+proj=longlat +ellps=WGS84")
gt <- makeGridTopology(grid.base, cellsize = c(1, 1))  # def grid topo

# time spent per cell
tppc <- tripGrid(tr, grid = gt)
tppc01 <- tppc               # a copy for pres/abs
tppc01 at data$z <- ifelse(tppc at data$z > 0, 1, 0)

image(tppc, col=rev(heat.colors(500)))  # seems ok
map('world', add=T)
points(coordinates(tr), t="l")

# but with presence/absence:
image(tppc01, col=c("white", "green"))
map('world', add=T)
points(coordinates(tr), t="l", col="blue")

Some ideas ?


Many thanks for your time.
David

-- 
***************************************************
David PINAUD
Ingénieur de Recherche "Analyses spatiales"

Centre d'Etudes Biologiques de Chizé - 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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