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

[Michael Sumner]

Thanks David, I'll investigate.

Also, I've been thinking there's probably no real reason not to allow
2-location trips. ;)

Cheers, Mike

2010/9/30 Pinaud David <pinaud at cebc.cnrs.fr>:
>  Hi Mike!
> I've fixed my problem by running this (unelegant) code, with the same idea
> as yours. I don't know if it's worth to include it in the trip package, but
> here is the code! Feel free to adapt it and use it if you want.
> I needed to change a little bit the trip class definition to convert a path
> with two locations in a trip object. You set the limit at 3 locs when
> defining a trip object, it makes sense that an interesting trip would have
> more than 3 locs, but some colleagues here are working with dispersal of
> individuals, calculating distance and bearing with 2 locs (birth / death or
> birth/first reproduction place), so the package can be also usefull in this
> case.
> Thanks
> David
>
> Le 09/09/2010 15:28, Michael Sumner a écrit :
>>
>> Sorry to have missed this.
>>
>> There's really no way to do this in longitude / latitude without a lot
>> of manual handling. You could split into two trips, one using the
>> eastern hemisphere, the other the western and use a shared [-180,180]
>> grid that you sum together.
>>
>> What to do at the split coordinate depends on your actual data, there
>> are many options.
>>
>> If you are still looking for an answer I could have a closer look at
>> your example code, but real data would be more helpful if you can
>> share it. There are a number of problems in the code you posted that
>> prevent it from being easily run.
>>
>> Cheers, Mike.
>>
>>
>>
>>
>> On Fri, Aug 6, 2010 at 8:10 PM, Pinaud David<pinaud at cebc.cnrs.fr>  wrote:
>>>
>>> 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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>>
>>
>
> --
> ***************************************************
> 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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> database 5492 (20100930) __________
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-- 
Michael Sumner
Institute for Marine and Antarctic Studies, University of Tasmania
Hobart, Australia
e-mail: mdsumner at gmail.com