\name{is.marked}
\alias{is.marked}
\title{Test Whether Marks Are Present}
\description{
  Generic function to test whether a given object (usually a point
  pattern or something related to a point pattern) has ``marks''
  attached to the points.
}
\usage{
  is.marked(X, \dots) 
}
\arguments{
  \item{X}{
    Object to be inspected
  }
  \item{\dots}{
    Other arguments.
  }
}
\value{
  Logical value, equal to \code{TRUE} if \code{X} is marked.
}
\details{
  ``Marks'' are observations attached to each point of a point pattern.
  For example the \code{\link{longleaf}} dataset contains the locations
  of trees, each tree being marked by its diameter;
  the \code{\link{amacrine}} dataset gives the locations of cells
  of two types (on/off) and the type of cell may be regarded as a mark attached
  to the location of the cell.

  Other objects related to point patterns, such as point process models,
  may involve marked points.

  This function tests whether the object \code{X}
  contains or involves marked points.
  It is generic; methods are provided
  for point patterns (objects of class \code{"ppp"})
  and point process models (objects of class \code{"ppm"}).
}
\seealso{
  \code{\link{is.marked.ppp}},
  \code{\link{is.marked.ppm}}
}
\author{Adrian Baddeley
  \email{Adrian.Baddeley@csiro.au}
  \url{http://www.maths.uwa.edu.au/~adrian/}
  and Rolf Turner
  \email{r.turner@auckland.ac.nz}
}
\keyword{spatial}
\keyword{manip}