Changing the origin in polar.plot in plotrix package

John Beamer wrote:

I am trying to draw a polar plot, which is easy enough to do in the
plotrix package through the polar.plot function.

However I would like to change the origin of the length vector. For
instance all my length values are between 75 and 85, so instead of
having the origin as 0 (the default) I'd like it to be, say, 50.

Is there any way do to this in the polar.plot function, or if not is
there an additional package that will accomplish this.

I am running R 2.5 and the latest version of plotrix.

Hi John,
The short answer is no.

The long answer is:

radial.plot<-function(lengths,radial.pos=NULL,
  labels=NA,label.pos=NULL,start=0,clockwise=FALSE,
  rp.type="r",label.prop=1.1,main="",xlab="",ylab="",
  line.col=par("fg"),mar=c(2,2,3,2),show.grid=TRUE,
  show.radial.grid=TRUE,grid.col="gray",
  grid.bg="transparent",grid.left=FALSE,
  point.symbols=NULL,point.col=NULL,
  show.centroid=FALSE,radial.lim=NULL,...) {

  if(is.null(radial.lim)) radial.lim<-range(lengths)
  length.dim<-dim(lengths)
  if(is.null(length.dim)) {
   npoints<-length(lengths)
   nsets<-1
   lengths<-matrix(lengths,nrow=1)
  }
  else {
   npoints<-length.dim[2]
   nsets<-length.dim[1]
   lengths<-as.matrix(lengths)
  }
  lengths<-lengths-radial.lim[1]
  lengths[lengths<0]<-NA
  if(is.null(radial.pos))
   radial.pos<-seq(0,pi*(2-2/npoints),length=npoints)
  radial.pos.dim<-dim(radial.pos)
  if(is.null(radial.pos.dim))
   radial.pos<-matrix(rep(radial.pos,nsets),
    nrow=nsets,byrow=TRUE)
  else radial.pos<-as.matrix(radial.pos)
  if(clockwise) radial.pos<--radial.pos
  if(start) radial.pos<-radial.pos+start
  if(show.grid) {
   grid.pos<-pretty(radial.lim)
   if(grid.pos[1] <= radial.lim[1])
    grid.pos<-grid.pos[-1]
   maxlength<-max(grid.pos-radial.lim[1])
   angles<-seq(0,1.96*pi,by=0.04*pi)
  }
  else {
   grid.pos<-NA
   maxlength<-diff(radial.lim)
  }
  oldpar<-par("xpd","mar","pty")
  par(mar=mar,pty="s")
  plot(c(-maxlength,maxlength),c(-maxlength,maxlength),
   type="n",axes=FALSE,
   main=main,xlab=xlab,ylab=ylab)
  par(xpd=TRUE)
  if(length(line.col) < nsets) line.col<-1:nsets
  rp.type<-unlist(strsplit(rp.type,""))
  if(match("s",rp.type,0)) {
   if(is.null(point.symbols)) point.symbols<-1:nsets
   if(length(point.symbols)<nsets)
    point.symbols<-rep(point.symbols,length.out=nsets)
   if(is.null(point.col)) point.col<-1:nsets
   if(length(point.col)<nsets)
    point.col<-rep(point.col,length.out=nsets)
  }
  # split up rp.type if there is a combination of displays
  for(i in 1:nsets) {
   # get the vector of x positions
   xpos<-cos(radial.pos[i,])*lengths[i,]
   # get the vector of y positions
   ypos<-sin(radial.pos[i,])*lengths[i,]
   # plot radial lines if rp.type == "r"
   if(match("r",rp.type,0))
    segments(0,0,xpos,ypos,col=line.col[i],...)
   if(match("p",rp.type,0))
    polygon(xpos,ypos,border=line.col[i],col=NA,...)
   if(match("s",rp.type,0))
    points(xpos,ypos,pch=point.symbols[i],
     col=point.col[i],...)
   if(show.centroid)
    points(mean(xpos),mean(ypos),col=point.col[i],
     pch=point.symbols[i],cex=2,...)
  }
  if(missing(labels)) {
   label.pos<-seq(0,1.8*pi,length=9)
   labels<-as.character(round(label.pos,2))
  }
  if(clockwise) label.pos<--label.pos
  if(start) label.pos<-label.pos+start
  xpos<-cos(label.pos)*maxlength
  ypos<-sin(label.pos)*maxlength
  if(show.radial.grid) segments(0,0,xpos,ypos,col=grid.col)
  xpos<-cos(label.pos)*maxlength*label.prop
  ypos<-sin(label.pos)*maxlength*label.prop
  boxed.labels(xpos,ypos,labels,ypad=0.7,border=FALSE)
  if(show.grid) {
   print(grid.pos)
   for(i in seq(length(grid.pos),1,by=-1)) {
    xpos<-cos(angles)*(grid.pos[i]-radial.lim[1])
    ypos<-sin(angles)*(grid.pos[i]-radial.lim[1])
    polygon(xpos,ypos,border=grid.col,col=grid.bg)
   }
   ypos<-rep(-maxlength/15,length(grid.pos))
   boxed.labels(grid.pos-radial.lim[1],ypos,
    as.character(grid.pos),border=FALSE)
  }
  par(oldpar)
}

But you will have to test it, and I would appreciate knowing if anything
breaks. Thanks.

Jim