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\name{computeContour3d}
\alias{computeContour3d}
\title{Compute Isosurface, a Three Dimension Contour}
\description{
Computes a 3D contours or isosurface by the marching cubes algorithm.
}
\usage{
computeContour3d(vol, maxvol = max(vol), level,
x = 1:dim(vol)[1],
y = 1:dim(vol)[2],
z = 1:dim(vol)[3], mask)
}
\arguments{
\item{vol}{a three dimensional array.}
\item{maxvol}{maximum of the \code{vol} array.}
\item{level}{The level at which to construct the contour surface.}
\item{x,y,z}{locations of grid planes at which values in \code{vol} are
measured.}
\item{mask}{a function of 3 arguments returning a logical array, a
three dimensional logical array, or \code{NULL}. If not
\code{NULL}, only cells for which \code{mask} is true at all eight
vertices are used in forming the contour.}
}
\value{
A matrix of three columns representing the triangles making up the
contour surface. Each row represents a vertex and goups of three
rows represent a triangle.
}
\details{
Uses the marching-cubes algorithm, with adjustments for dealing with
face and internal ambiguities, to compute an isosurface.
See references for the details. The function
\code{\link[misc3d]{contour3d}} provides a higher-level interface.
}
\references{
Chernyaev E. (1995)
Marching Cubes 33: Construction of Topologically Correct Isosurfaces
\emph{Technical Report CN/95-17, CERN}
Lorensen W. and Cline H. (1987)
Marching Cubes: A High Resolution 3D Surface Reconstruction Algorithm
\emph{Computer Graphics} \bold{vol. 21, no. 4}, 163-169
Nielson G. and Hamann B. (1992)
The Asymptotic Decider: Resolving the Ambiguity in Marching Cubes
\emph{Proc. IEEE Visualization} \bold{92}, 83-91
}
\seealso{
\code{\link[misc3d]{contour3d}}
}
\examples{
x <- seq(-2,2,len=50)
g <- expand.grid(x = x, y = x, z = x)
v <- array(g$x^4 + g$y^4 + g$z^4, rep(length(x),3))
con <- computeContour3d(v, max(v), 1)
drawScene(makeTriangles(con))
}
\keyword{hplot}
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