[R] Ternary Plots Do Not Display Ellipses in PDF

[Rich Shepard]

   A rather strange situation here and I've not found the source of the
problem.

   The point is to print a ternary plot matrix of compositional data with
ellipses enclosing 95% of the variance in each plot. The ellipses display on
the monitor, dev = x11cairo, but not when sent directly to a file, dev =
pdf.

   Here's winters.acomp:

structure(c(0.0666666666666667, 0.0612244897959184, 0.0434782608695652, 
0.043956043956044, 0.05, 0.0161290322580645, 0.6, 0.571428571428571, 
0.623188405797101, 0.593406593406593, 0.433333333333333, 0.629032258064516, 
0.0666666666666667, 0.0612244897959184, 0.101449275362319, 0.0659340659340659, 
0.0666666666666667, 0.032258064516129, 0.244444444444444, 0.26530612244898, 
0.217391304347826, 0.263736263736264, 0.366666666666667, 0.290322580645161, 
0.0222222222222222, 0.0408163265306122, 0.0144927536231884, 0.032967032967033, 
0.0833333333333333, 0.032258064516129), .Dim = c(6L, 5L), .Dimnames = list(
     NULL, c("filter", "gather", "graze", "predate", "shred")), class = "acomp")

   And this is the command sequence:

> library(compositions)
> plot(winters.acomp, main="Winters Creek", cex=0.5)
> r <- sqrt(qchisq(p=0.95, df=4))
> mn <- mean(winters.acomp)
> vr <- var(winters.acomp)
> plot(winters.acomp, main="Winters Creek", cex=0.5)
> ellipses(mean=mn, var=vr, r=r, steps=72, thinRatio=NULL, aspanel=FALSE,
 	col='red', lwd=2)
# monitor plot window is manually closed.
> pdf("winters-pdf.pdf")
> plot(winters.acomp, main="Winters Creek", cex=0.5)
> ellipses(mean=mn, var=vr, r=r, steps=72, thinRatio=NULL, aspanel=FALSE,
 	col='red', lwd=2)
> dev.off()

   What am I not seeing here that causes the different outputs?

Rich