model.matrix.ppm.Rd
\name{model.matrix.ppm}
\alias{model.matrix.ppm}
\title{Extract Design Matrix from Point Process Model}
\description{
Given a point process model that has been
fitted to spatial point pattern data,
this function extracts the design matrix of the model.
}
\usage{
\method{model.matrix}{ppm}(object, ..., keepNA=TRUE)
}
\arguments{
\item{object}{
The fitted point process model (an object of class \code{"ppm"}.)
}
\item{keepNA}{
Logical. Determines whether rows containing NA values will be
deleted or retained.
}
\item{\dots}{
Other arguments (such as \code{na.action}) passed to
\code{\link{model.matrix.lm}}.
}
}
\details{
This command is a method for the generic function
\code{\link{model.matrix}}. It extracts the design matrix of a
spatial point process model (class \code{"ppm"}).
More precisely, this command extracts
the design matrix of the generalised linear model associated with
a spatial point process model.
The \code{object} must be a fitted point process model
(object of class \code{"ppm"}) fitted to spatial point pattern data.
Such objects are produced by the model-fitting
function \code{\link{ppm}}.
This function \code{model.matrix.ppm}
extracts the model matrix for the GLM.
The result is a matrix, with one row for every quadrature point
in the fitting procedure, and one column for every constructed
covariate in the design matrix.
If there are \code{NA} values in the covariates,
the argument \code{keepNA} determines whether to retain or delete
the corresponding rows of the model matrix. The default
\code{keepNA=TRUE} is to retain them. Note that this differs from
the default behaviour of many other methods for \code{model.matrix},
which typically delete rows containing \code{NA}.
The quadrature points themselves can be extracted using
\code{\link{quad.ppm}}.
}
\value{
A matrix. Rows of the matrix correspond to quadrature points
in the fitting procedure (provided \code{keepNA=TRUE}).
Columns are covariates in the model.
}
\author{Adrian Baddeley
\email{adrian@maths.uwa.edu.au}
\url{http://www.maths.uwa.edu.au/~adrian/}
and Rolf Turner
\email{r.turner@auckland.ac.nz}
}
\seealso{
\code{\link{model.images}},
\code{\link{ppm}},
\code{\link{ppm.object}},
\code{\link{quad.ppm}},
\code{\link{residuals.ppm}},
\code{\link{model.matrix}}
}
\examples{
data(cells)
fit <- ppm(cells, ~x)
model.matrix(fit)
# matrix with two columns: '(Intercept)' and 'x'
}
\keyword{spatial}
\keyword{models}