[AniMov] summing BB outputs

S. Skrafner s.skrafner at gmail.com
Tue May 17 21:55:52 CEST 2011


Hello,



I am looking for some advice.  I’ve been struggling with tyring to combine
Brownian Bridge UD’s of the class estUD for work similar to that carried out
by Sawyer et al (Ecological Applications 2009, 19:2016-2025).  My goal is to
get some ideas of common space use (similar to migration corridors) for my
animals by summing the individual UD’s and rescaling to a single probability
surface.



I have created the BB probability surfaces using the function kernelbb which
creates a class estUD.  What I am having trouble with is determining how to
sum the different surfaces so that I can then rescale the cumulative values
back to 1 and then create a Volume surface using getvolumeUD.  Any
suggestions on how I would go about summing the different UD’s would be
extremely helpful.



I hope that makes sense and I've provided enough information.


An example of the code I am using for a single animal is below:


###################################

# data is in a data.frame named 'temp'

gridbox <- data.frame(x=c(min(na.omit(temp$x))-15000,
max(na.omit(temp$x))+15000), y = c(min(na.omit(temp$y))-15000,
max(na.omit(temp$y))+15000))
gridbox<-SpatialPoints(gridbox)
ascgrid <- ascgen(gridbox, cellsize=500)

xy<-temp[,c("x","y")]
da<- as.POSIXct(strptime(as.character(temp$Date), "%d/%m/%Y %X"))
 #create an animal trajectory
tr <- as.ltraj(xy[temp$AnID==j,], date = da[temp$AnID==j], id=j)
tr2 <- setNA(tr, tr[[1]]$date[1], dt=4, units="hour")
tr<- tr2


sig <- liker(tr, sig2 = sig.2, rangesig1=c(1,100), le=2500)

bb.out <- kernelbb(tr, sig1 = sig.num, sig2 = sig.2, grid = ascgrid, extent
= 0.5)

vol.out <- getvolumeUD(bb.out)

###################################


Thanks in advance,

Steve
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