[AniMov] R package ADEhabitatLT - function ltraj/cutltraj - bursts

Calenge Clement Clement.Calenge at oncfs.gouv.fr
Thu Oct 9 15:41:51 CEST 2014


On 09/10/2014 15:36, Michael Sumner wrote:
> Would it not be ok to just interpolate a redundant point between the
> two? Then you don't fall foul of the rules?

yes, that would be a better solution (no need to edit the function then).
All the best,

Clément

>
> That seems safer and more reproducible than moving the ground under your feet?
>
> (Just my 2 cents having not tested either path).
>
> Cheers, Mike.
>
> On Thu, Oct 9, 2014 at 9:57 PM, Calenge Clement
> <Clement.Calenge at oncfs.gouv.fr> wrote:
>>
>>> I have a question concerning the ADEhabitatLT package in R. We are
>>> analyzing GPS data of beavers sampled at an 15 min interval from approx.
>>> 7 pm  - 7 am for 7 nights. The aim of our study is to look at changes in
>>> movement behavior after capture (we tag them with GPS units and release
>>> them afterwards).
>>>
>>> We used the ltraj function to create an ltraj object with bursts for
>>> every individual. We then divided the bursts into sub-bursts for every
>>> night with cutltraj by using time lags over 8 hrs (when beavers are
>>> inside the lodge during daytime) for splitting up. However, we get a
>>> warning message saying that
>>>
>>> Warning message:
>>>
>>> In cutltraj(Beav, "foo(dt)", nextr = TRUE) :
>>>
>>>     At least 3 relocations are needed for a burst
>>>
>>> 9 relocations have been deleted
>>>
>>> For our purpose, the first night after capture is really important. And
>>> just for this night, we sometimes only got 2 relocations since the
>>> animals went into their lodge (no GPS signal), meaning that the function
>>> just deletes the first night for some of our animals. We thus would like
>>> to include these bursts for analysis and wonder whether there is a
>>> possibility to create a burst with only 2 relocations?
>>
>> Some of the statistics used to describe the trajectory require at least
>> two steps, i.e. 3 relocations  (e.g. the relative angle, or turning
>> angles, between successive steps). However, if you insist, you can edit
>> the function cutltraj, e.g. using the command:
>>
>> cultraj<-edit(cutltraj)
>>
>> and delete the following commands at the end of the function:
>>
>>       resb <- res[rrr >= 3]
>>       if (length(res) != length(resb))
>>           warning(paste("At least 3 relocations are needed for a burst\n",
>>               sum(rrr[rrr < 3]), "relocations have been deleted"))
>>
>> This will avoid this unwanted behaviour. However, I cannot guarantee
>> that the other functions in adehabitatLT will work with a 2-relocations
>> ltraj (Two relocations do not define a trajectory; you need at least
>> three). You are on your own if you decide to do that!
>>
>> HTH,
>>
>> Clément Calenge
>> --
>> Clément CALENGE
>> Cellule d'appui à l'analyse de données
>> Direction des Etudes et de la Recherche
>> Office national de la chasse et de la faune sauvage
>> Saint Benoist - 78610 Auffargis
>> tel. (33) 01.30.46.54.14
>> _______________________________________________
>> AniMov mailing list
>> AniMov at faunalia.it
>> http://lists.faunalia.it/cgi-bin/mailman/listinfo/animov
>
>
>


-- 
Clément CALENGE
Cellule d'appui à l'analyse de données
Direction des Etudes et de la Recherche
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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