Create the “dividing chain” of a Dirchlet tesselation. The tessellation must have been created from a set of points having associated categorical “weights”. The dividing chain consists of those edges of Dirichlet tiles which separate points having different values of the given weights.
# S3 method for deldir
divchain(x, ...)An object of class “deldir”. This object must have
been created in such a way that the points of the set being
tessellated have associate categorical “weights”. That is,
deldir() must have been called with a factor
valued z argument or the x argument to deldir()
must have had an appropriate component which could be taken to
be z.
Not used.
An object of class “divchain” consisting of a data frame with columns named “x0”, “y0”, “x1”,“y1”, “v01”, “v02”, “v03”, “v11”, “v12” and “v13”.
The columns named “x0” and “y0” consist of the coordinates of one endpoint of an edge of a Dirichlet tile and the columns named “x1” and “y1” consist of the coordinates of the other endpoint.
The columns named “vij”, i = 0, 1, j = 1, 2, 3, consist
of the indices of the vertices of the Delaunay triangles
whose circumcentres constitute the respective endpoints of the
corresponding edge of a Dirichlet tile. The entries of column
“vi3” may (also) take the values $-1, -2, -3$, and $-4$.
This will be the case if the circumcentre in question lay outside
of the rectangular window rw (see deldir())
enclosing the points being tessellated. In these circumstances the
corresponding endpoint of the tile edge is the intersection of the
line joining the two circumcentres with the boundary of rw,
and the numeric value of the entry of column “vi3” indicates
which side. The numbering follows the convention for numbering
the sides of a plot region in R: 1 for the bottom side,
2 for the left side, 3 for the top side and 4 for the right side.
Note that the triple of vertices uniquely identify the endpoint of the tile edge.
The object has an attribute rw which is equal to the
specification of the rectangular window within which the
class “deldir” object x was constructed.
(See deldir().)
# NOT RUN {
set.seed(42)
x <- runif(50)
y <- runif(50)
z <- factor(kmeans(cbind(x,y),centers=4)$cluster)
dxy <- deldir(x,y,z=z,rw=c(0,1,0,1))
dc <- divchain(dxy)
# }
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