Dear List,
After solving the last problem (thanks to you), I'm now having some
trouble in performing a first passage time analysis.
It seems that the most important step of this analysis is to define
the scale "r". But, how do I choose the "optimal" radii?
The example given by R Help (adehabitat manual) is the following:
data(puechcirc)
i <- fpt(puechcirc, seq(300,1000, length=30))
plot(i, scale = 500, warn = FALSE)
Could someone explain to me the above mentioned steps?
"puechirc" is an object of class "ltraj", but what does "
seq(300,1000, length=30))" stands for?
and "scale = 500" is the radius?
Another example which I don't understand entirely:
scales<-c(2, seq(5, 45, 5), seq(50, 500, 25)) #what does it mean?
a.cut <- FPT.cut(file=loc1, Long=loc1$Long, Lat=loc1$Lat,
Date=loc1$DateD, d=2) #cut the trip into intermediate locations of
2km, but R doesn't recognise "FPT.cut"
a.fpt <- FPT.calc(a.cut, r=scales) # FPT for the specified
scales (it can be quite long!)
I have an object of class "ltraj" (tr <- as.ltraj(TB2[,
c("LON","LAT")], TB2$Date, TB2$Bird) containing the relocations of
Birds. Further, the maximum foraging trip duration is 35h, total
distance travelled: 426km, max. distance from the nest: 162km. GPS
recorded a fix every 5 min (some GPS every 2min and every 4 min
depending on the tag used). With the fpt I would like to determine the
ARS of each individual. From my data set, it seems that the birds
mainly forage at the farthest point of the track and sometimes on the
way back to the colony.
Now, how do I define the scales where fpt will be calculated? And how
do I calculate my fpt? Would it be helpful cutting the tracks into
intermediate locations of 2km for example and then to calculate the
fpt for a defined scale?
I'm still a R beginner, thus apologies in advance in case I ask some
"obvious" stuff.
Thank you in advance for any ideas and suggestions. I would also
highly appreciate recommendations of manuals, books or papers on this
issue, although I think I have got most of them.
Best regards,
Julia
Julia Sommerfeld - PhD Candidate
Institute for Marine and Antarctic Studies
University of Tasmania
Private Bag 129, Hobart
TAS 7001
Phone: +61 458 247 348
Email: [email protected]
[email protected]
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