Mask Buffer Width
Determines a suitable buffer width for an integration mask. The
‘buffer’ in question defines a concave polygon around a detector array
constructed using make.mask with type = "trapbuffer". The
method relies on an approximation to the bias of maximum likelihood
density estimates (M. Efford unpubl).
suggest.buffer(object, detectfn = NULL, detectpar = NULL,
noccasions = NULL, ignoreusage = FALSE, ncores = NULL, RBtarget = 0.001,
interval = NULL, binomN = NULL, ...)
bias.D (buffer, traps, detectfn, detectpar, noccasions, binomN = NULL,
control = NULL)object |
single-session ‘secr’, ‘traps’ or ‘capthist’ object |
detectfn |
integer code or character string for shape of detection function 0 = halfnormal etc. – see detectfn |
detectpar |
list of values for named parameters of detection function – see detectpar |
noccasions |
number of sampling occasions |
ignoreusage |
logical for whether to discard usage information from
|
ncores |
integer number of threads to use for parallel processing |
RBtarget |
numeric target for relative bias of density estimate |
interval |
a vector containing the end-points of the interval to be searched |
binomN |
integer code for distribution of counts (see
|
... |
other argument(s) passed to |
buffer |
vector of buffer widths |
traps |
‘traps’ object |
control |
list of mostly obscure numerical settings (see Details) |
The basic input style of suggest.buffer uses a ‘traps’ object and
a detection model specified by ‘detectpar’, ‘detectfn’ and ‘noccasions’,
plus a target relative bias (RB). A numerical search is conducted for
the buffer width that is predicted to deliver the requested RB. If
interval is omitted it defaults to (1, 100S) where S is the
spatial scale of the detection function (usually
detectpar$sigma). An error is reported if the required buffer
width is not within interval. This often happens with
heavy-tailed detection functions (e.g., hazard-rate): choose another
function, a larger RBtarget or a wider interval.
Setting ncores = NULL uses the existing value from the environment variable
RCPP_PARALLEL_NUM_THREADS (see setNumThreads).
Convenient alternative input styles are –
secr object containing a fitted model. Values of ‘traps’,
‘detectpar’, ‘detectfn’ and ‘noccasions’ are extracted from
object and any values supplied for these arguments are ignored.
capthist object containing raw data. If detectpar is
not supplied then autoini is used to get ‘quick and dirty’
values of g0 and sigma for a halfnormal detection
function. noccasions is ignored. autoini tends to
underestimate sigma, and the resulting buffer also tends to be
too small.
bias.D is called internally by suggest.buffer.
suggest.buffer returns a scalar value for the suggested buffer
width in metres, or a vector of such values in the case of a
multi-session object.
bias.D returns a dataframe with columns buffer and RB.D
(approximate bias of density estimate using finite buffer width,
relative to estimate with infinite buffer).
The algorithm in bias.D uses one-dimensional numerical
integration of a polar approximation to site-specific detection
probability. This uses a further 3-part linear approximation for the
length of contours of distance-to-nearest-detector (r) as a
function of r.
The approximation seems to work well for a compact detector array, but
it should not be taken as an estimate of the bias for any other purpose:
do not report RB.D as "the relative bias of the density
estimate". RB.D addresses only the effect of using a finite
buffer. The effect of buffer width on final estimates should be checked
with mask.check.
The default buffer type in make.mask, and hence in
secr.fit, is ‘traprect’, not ‘trapbuffer’, but a buffer width
that is adequate for ‘trapbuffer’ is always adequate for ‘traprect’.
control contains various settings of little interest to the
user.
The potential components of control are –
method = 1 code for method of modelling p.(X) as a function of buffer (q(r))
bfactor = 20 q(r) vs p.(X) calibration mask buffer width in multiples of trap spacing
masksample = 1000 maximum number of points sampled from calibration mask
spline.df = 10 effective degrees of freedom for
smooth.spline
ncores = NULLinteger number of cores
temptraps <- make.grid() detpar <- list(g0 = 0.2, sigma = 25) suggest.buffer(temptraps, "halfnormal", detpar, 5) ## Not run: suggest.buffer(secrdemo.0) suggest.buffer(ovenCH[[1]]) RB <- bias.D(50:150, temptraps, "halfnormal", detpar, 5) plot(RB) detpar <- list(g0 = 0.2, sigma = 25, z=5) RB <- bias.D(50:150, temptraps, "hazard rate", detpar, 5) lines(RB) ## compare to esa plot esa.plot (temptraps, max.buffer = 150, spacing = 4, detectfn = 0, detectpar = detpar, noccasions = 5, type = "density") ## compare detection histories and fitted model as input suggest.buffer(captdata) suggest.buffer(secrdemo.0) ## End(Not run)
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