[pstricks] Disappearing points

[John Culleton]

I take a given file and draw a \psccurve with [showpoints=yes]
parameter.

I run the file through tex and dvips -Ppdf

If I display the result using gv the curve appears and the points of
the curve are also shown.

If i then convert it to a pdf using ps2pdf and display the result
using acroread the curve is still there but the points have
disappeared. 

 If I display it using xpdf the points have also disappeared.

So the line drawing function of pstricks passes through to the pdf
file but the points do not.  

Can someone cite a general rule for what pieces of pstricks
will pass through ps2pdf and what pieces won't.?

John Culleton
john at wexfordpress.net