secr (version 3.2.1)

make.systematic: Construct Systematic Detector Design

Description

A rectangular grid of clusters within a polygonal region.

Usage

make.systematic(n, cluster, region, spacing = NULL, origin = NULL, 
    originoffset = c(0,0), chequerboard = c('all','black','white'), ...)

Arguments

n

integer approximate number of clusters (see Details)

cluster

traps object defining a single cluster

region

dataframe or SpatialPolygonsDataFrame with coordinates of perimeter

spacing

scalar distance between cluster centres

origin

vector giving x- and y-cooordinates of fixed grid origin (origin is otherwise random)

originoffset

numeric; 2-vector (x,y offsets); see Details

chequerboard

logical; if not `all' then alternate clusters are omitted

…

arguments passed to trap.builder

Value

A single-session `traps' object.

From 3.2.0 these additional attributes are set --

origin	coordinates of grid origin	centres
coordinates of true cluster centres (cf cluster.centres)	originbox	vertices of rectangular spatial sampling frame for random origin

Details

region may be any shape. The sp class SpatialPolygonsDataFrame is useful for complex shapes and input from shapefiles using rgdal (see Examples). Otherwise, region should be a dataframe with columns `x' and `y'.

spacing may be a vector with separate values for spacing in x- and y- directions. If spacing is provided then n is ignored.

If n is a scalar, the spacing of clusters is determined from the area of the bounding box of region divided by the requested number of clusters (this does not necessarily result in exactly n clusters). If n is a vector of two integers these are taken to be the number of columns and the number of rows.

After preparing a frame of cluster centres, make.systematic calls trap.builder with method = `all'; … allows the arguments `rotation', `edgemethod', `plt', and `detector' to be passed. Setting the trap.builder arguments frame, method, and samplefactor has no effect.

If origin is not specified then a random uniform origin is chosen within a box (width = spacing) placed with its bottom left corner at the bottom left of the bounding box of region, shifted by originoffset. Before version 3.1.8 the behaviour of make.systematic was equivalent to originoffset = c(wx,wy) where wx,wy are the cluster half widths.

chequerboard = "black" retains black `squares' and chequerboard = "white" retains white `squares', where the lower left cluster in the candidate rectangle of cluster origins is black, as on a chess board. The effect is the same as increasing spacing by sqrt(2) and rotating through 45 degrees.

See Also

trap.builder, cluster.centres, readOGR

Examples

# NOT RUN {
mini <- make.grid(nx = 2, ny = 2, spacing = 100)
region <- cbind(x=c(0,2000,2000,0), y=c(0,0,2000,2000))
temp <- make.systematic(25, mini, region, plt = TRUE)
temp <- make.systematic(c(6, 6), mini, region, plt = TRUE,
    rotation = -1)

## Example using shapefile "possumarea.shp" in
## "extdata" folder. By default, each cluster is 
## a single multi-catch detector

# }
# NOT RUN {
datadir <- system.file("extdata", package = "secr")
possumarea <- rgdal::readOGR(dsn = datadir, layer = "possumarea")

possumgrid <- make.systematic(spacing = 100, region =
    possumarea, plt = TRUE)

## or with 2 x 2 clusters
possumgrid2 <- make.systematic(spacing = 300,
    cluster = make.grid(nx = 2, ny = 2, spacing = 100),
    region = possumarea, plt = TRUE, edgemethod =
    "allinside")
## label clusters
text(cluster.centres(possumgrid2), levels(clusterID
    (possumgrid2)), cex=0.7)

## If you have GPSBabel installed and on the Path
## then coordinates can be projected and uploaded
## to a GPS with `writeGPS', which also requires the
## package `proj4'. Defaults are for a Garmin GPS
## connected by USB.

writeGPS(possumgrid, proj = "+proj=nzmg")

# }
# NOT RUN {
# }