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

Patricia Maria Graf patricia.m.graf at hit.no
Thu Oct 9 16:21:47 CEST 2014


Thanks a lot for your advice, we managed to solve the problem by interpolating a redundant point!

All the best,
Patricia


-----Opprinnelig melding-----
Fra: AniMov [mailto:animov-bounces at faunalia.it] På vegne av Calenge Clement
Sendt: 9. oktober 2014 15:42
Til: Animal Movement
Emne: Re: [AniMov] R package ADEhabitatLT - function ltraj/cutltraj - bursts

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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