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

Michael Sumner mdsumner at gmail.com
Thu Oct 9 15:32:53 CEST 2014

Would it not be ok to just interpolate a redundant point between the
two? Then you don't fall foul of the rules?

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)
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Michael Sumner
Software and Database Engineer
Australian Antarctic Division
Hobart, Australia
e-mail: mdsumner at gmail.com

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