gridweights
Compute Quadrature Weights Based on Grid Counts
Computes quadrature weights for a given set of points, using the ``counting weights'' for a grid of rectangular tiles.
Usage
gridweights(X, ntile, ..., window=NULL, verbose=FALSE, npix=NULL, areas=NULL)Arguments
- X
- Data defining a point pattern.
- ntile
- Number of tiles in each row and column of the rectangular grid. An integer vector of length 1 or 2.
- ...
- Ignored.
- window
- Default window for the point pattern
- verbose
- Logical flag. If
TRUE, information will be printed about the computation of the grid weights. - npix
- Dimensions of pixel grid to use when computing a digital approximation to the tile areas.
- areas
- Vector of areas of the tiles, if they are already known.
Details
This function computes a set of quadrature weights
for a given pattern of points
(typically comprising both ``data'' and `dummy'' points).
See quad.object for an explanation of quadrature
weights and quadrature schemes.
The weights are computed by the ``counting weights'' rule
based on a regular grid of rectangular tiles.
First X and (optionally) window are converted into a
point pattern object. Then the bounding rectangle of the window of
the point pattern is
divided into a regular ntile[1] * ntile[2] grid of rectangular tiles.
The weight attached to a point of X is the area of the tile
in which it lies, divided by the number of points of X lying in
that tile.
For non-rectangular windows the tile areas are currently calculated
by approximating the window as a binary mask. The accuracy of this
approximation is controlled by npix, which becomes
the argument dimyx of as.mask.
Value
- Vector of nonnegative weights for each point in
X.
See Also
Examples
Q <- quadscheme(runifpoispp(10))
X <- as.ppp(Q) # data and dummy points together
w <- gridweights(X, 10)
w <- gridweights(X, c(10, 10))