Description Usage Arguments Details Value See Also
Numerically estimate the c2
parameter for fbtgUD
using a data-driven approach.
1 2 |
traj |
animal movement trajectory in the form of an |
tl |
a |
timefun |
method for converting time into probability (see |
sigma |
location uncertainty parameter (see fbtgUD) |
lower |
lower bound for |
upper |
upper bound for |
rand |
if |
niter |
used to define maximum number of iterations of golden-search routine |
tolerance |
used to define precision of golden search routine (i.e., routine stops when the absolute difference between two consecutive test points is below this value). |
plot |
logical, whether or not to plot the log-likelihood curve. |
THe estimation of the c2
parameter for fbtgUD
model takes an identical approach to that used with Brownian bridges, as originally proposed by Horne et al. (2007). A leave-one-out estimation technique is used, which essentially removes fixes and then estimates the fbtgUD surface between the two adjacent fixes – termed a segment – and computes the probability associated with the missing fix. The c2
value is returned that numerically maximizes the log-likelihood (for a given timefun
– see details in fbtgUD
) for length.out
evenly spaced values of c2
between (user-defined) min
and max
. With plot = TRUE
the user can verify that the chosen range of potential c2
values is appropriate, and if not, retry using a differnt range. The process is computationally demanding and is highly dependent on the number of 'segments' used. The parameter rand
can be used to adjust the number of segments used to minimize computational time. If rand = NA
it removes every second fix, and estimates c2
based on these n/2 segments (the default). Otherwise rand
can be passed in as an integer, and rand
randomly selected segments will be chosen to estimate c2
. This is beneficial for trajectories with many fixes, where it might be useful to choose rand <<< n/2
. Parrallelization is possible to further decrease computational time. This can be implemented by choosing an appropriate integer value for the parallel
parameter (implemented using the foreach
package).
This function returns a numerical value estimate for c2
associated with the maximum of the log-likelihood.
fbtgUD
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