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plot.deldir

Plot objects produced by deldir

Description

This is a method for plot.

Usage

## S3 method for class 'deldir'
plot(x,add=FALSE,wlines=c('both','triang','tess'),
                      wpoints=c('both','real','dummy','none'),
                      number=FALSE,cex=1,nex=1,cmpnt_col=NULL,cmpnt_lty=NULL,
                      pch=NULL,xlim=NULL,ylim=NULL,axes=FALSE,
                      xlab=if(axes) 'x' else '',ylab=if(axes) 'y' else'',
                      showrect=FALSE,asp=1,...)

Arguments

x

An object of class "deldir" as returned by the function deldir.

add

logical argument; should the plot be added to an existing plot?

wlines

"which lines?". I.e. should the Delaunay triangulation be plotted (wlines='triang'), should the Dirichlet tessellation be plotted (wlines='tess'), or should both be plotted (wlines='both', the default) ?

wpoints

"Which points to plot?". I.e. should the real points be plotted (wpoints='real'), should the dummy points be plotted (wpoints='dummy'), should both be plotted (wpoints='both', the default) or should no points be plotted (wpoints='none')?

number

Logical argument, defaulting to FALSE; if TRUE then the points plotted will be labelled with their index numbers (corresponding to the row numbers of the matrix "summary" in the output of deldir).

cex

The value of the character expansion argument cex to be used with the plotting symbols for plotting the points.

nex

The value of the character expansion argument cex to be used by the text function when numbering the points with their indices. Used only if number=TRUE.

cmpnt_col

A vector or list specifying the colours to be used for plotting the (up to six) different components of the graphic, explictly the triangulation, the tesselation, the data points, the dummy points, the point numbers and the enclosing rectangle (x$rw) in that order. The components of this vector or list may be named, with the names chosen from "tri","tess","data","dummy","num","rect". The default is c(tri=1,tess=1,data=1,dummy=1,num=1,rect=1). If the vector or list is not named, the component names are assumed to be from the default list of names in the given order.

Colours may be specified as positive integers, corresponding to the entries of the current palette(), or as names of colours (from the list given by link{colors}()), or in terms of their RGB components with strings of the form "#RRGGBB". (See Color Specification in par().)

If fewer than six colours are given, the missing components are filled in with 1 or palette()[1] as is appropriate. If cmpnt_col does not have names then the components are simply recycled. If more than six colours are given, the redundant ones are ignored (i.e. only the first six are used).

cmpnt_lty

A vector or list (of length two) of line type numbers for plotting the two components of the graphic that consist of lines, i.e. the triangulation and the tesselation. The components of this vector or list may have names ("tri","tess"). The default is c(tri=1,tess=1). If a single value is given the missing one is filled in as 1. If more than two numbers are given, the redundant ones are ignored, i.e. only the first two are used. See par() for the meaning of these numbers.

pch

The plotting symbols for plotting the data points and the dummy points, in that order; may be either integer or character; defaults to 1:2. If only one value is given it is repeated. (If more than two values are given, the redundant ones are ignored.)

xlim

The limits on the x-axis. Defaults to rw[1:2] where rw is the rectangular window specification returned by deldir().

ylim

The limits on the y-axis. Defaults to rw[3:4] where rw is the rectangular window specification returned by deldir().

axes

Logical scalar. Should axes be drawn on the plot?

xlab

Label for the x-axis. Defaults to x if axes is TRUE and to the empty string if axes is FALSE. Ignored if add=TRUE.

ylab

Label for the y-axis. Defaults to y if axes is TRUE and to the empty string if axes is FALSE. Ignored if add=TRUE.

showrect

Logical scalar; show the enclosing rectangle rw (see deldir()) be plotted?

asp

The aspect ratio of the plot; integer scalar or NA. Set this argument equal to NA to allow the data to determine the aspect ratio and hence to make the plot occupy the complete plotting region in both x and y directions. This is inadvisable; see the Warning. The asp argument is ignored if add is TRUE.

...

Further plotting parameters (e.g. lw, col) to be passed to segments(). (Conceivably one might also use ... to supply additional arguments to be passed to points() or text() but this is unlikely.) Note that if col is specified as one of the ... arguments then this is used as the col argument of segments (and the values of cmpnt_col[1:2] are ignored.

Details

The points in the set being triangulated are plotted with distinguishing symbols. By default the real points are plotted as circles (pch=1) and the dummy points are plotted as triangles (pch=2).

Side Effects

A plot of the edges of the Delaunay triangles and/or of the Dirichlet tiles is produced or added to an existing plot. By default the triangles are plotted with solid lines (lty=1) and the tiles with dotted lines (lty=2). In addition the (data and dummy) points being triangulated may be plotted.

Warning

In previous versions of the deldir package, the aspect ratio was not set. Instead, the shape of the plotting region was set to be square (pty="s"). This practice was suboptimal. To reproduce previous behaviour set asp=NA (and possibly pty="s") in the call to plot.deldir(). Users, unless they really understand what they are doing and why they are doing it, are now strongly advised not to set the value of asp but rather to leave asp equal to its default value of 1. Any other value may distort the tesselation and destroy the perpendicular appearance of lines which are indeed perpendicular. (And conversely may cause lines which are not perpendicular to appear as if they are.)

Author(s)

See Also

Examples

x <- c(2.3,3.0,7.0,1.0,3.0,8.0) + 0.5
y <- c(2.3,3.0,2.0,5.0,8.0,9.0) + 0.5
dxy <- deldir(x,y,dpl=list(x=c(1,10,10,1),y=c(1,1,10,10)),rw=c(0,11,0,11))
plot(dxy)

# Plots the tesselation, but does not save the results:
deldir(x,y,dpl=list(x=c(1,10,10,1),y=c(1,1,10,10),rw=c(0,11,0,11)),plot=TRUE,
       wl='tess',cmpnt_col=c(1,1,2,3,4,5),num=TRUE)

# Plots the triangulation, but not the tessellation or the points,
# and saves the returned structure:

dxy <- deldir(x,y,dpl=list(x=c(1,10,10,1),y=c(1,1,10,10)),rw=c(0,11,0,11),plot=TRUE,
       wl='triang',wp="none")

# Plot everything:
plot(dxy,cmpnt_col=c("orange","green","red","blue","black","black"),cmpnt_lty=1,
     number=TRUE,nex=1.5,pch=c(19,9),showrect=TRUE,axes=TRUE)

# Complicated example from He Huang:
# "Linguistic distances".
vldm <- c(308.298557,592.555483,284.256926,141.421356,449.719913,
          733.976839,591.141269,282.842712,1.414214,732.562625)
ldm <- matrix(nrow=5,ncol=5)
ldm[row(ldm) > col(ldm)]  <- vldm
ldm[row(ldm) <= col(ldm)] <- 0
ldm <- (ldm + t(ldm))/2
rownames(ldm) <- LETTERS[1:5]
colnames(ldm) <- LETTERS[1:5]

# Data to be triangulated.
id <- c("A","B","C","D","E")
x  <- c(0.5,1,1,1.5,2)
y  <- c(5.5,3,7,6.5,5)
dat_Huang <- data.frame(id = id, x = x, y = y)

# Form the triangulation/tessellation.
dH <- deldir(dat_Huang)

# Plot the triangulation with line widths proportional
# to "linguistic distances".
all_col <- rainbow(100)
i       <- pmax(1,round(100*vldm/max(vldm)))
use_col <- all_col[i]
ind     <- as.matrix(dH$delsgs[,c("ind1","ind2")])
lwv <- ldm[ind]
lwv <- 10*lwv/max(lwv)
plot(dH,wlines="triang",col=use_col,wpoints="none",
     lw=lwv,asp=NA)
with(dH,text(x,y,id,cex=1.5))
deldir

Delaunay Triangulation and Dirichlet (Voronoi) Tessellation

v0.2-10
GPL (>= 2)
Authors
Rolf Turner
Initial release
2021-02-16

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