[pstricks] Defining a maxmum and minimum point

[Herbert Voss]

Arne Hallam wrote:
> ions (which I can easily do).
>
> Show a small circle or disc at (x1,x2,0) in the x1-x2 plane(which I 
> cannot do)
>   

with pst-3dplot you have a parallel projection and
with pst-vue3d a central projection

\documentclass[12pt]{article}

\usepackage{pstricks}
\usepackage{pst-3dplot,pst-vue3d}

\begin{document}

\begin{pspicture}(-2,-1.25)(2,3)
  \psset{Beta=10,Alpha=30}
  \pstThreeDCoor[xMax=2,yMax=2,zMax=4,linecolor=black,linestyle=dashed]
  \psset{linecolor=red,linewidth=2pt}
  \pstThreeDCircle(0,0,0)(1.5,0,0)(0,1.5,0)
  \pstThreeDCircle[linecolor=green](0,0,1)(1.5,0,0)(0,1.5,0)
 
\pstThreeDCircle[linecolor=blue,fillstyle=solid,fillcolor=blue](0,0,2)(1.5,0,0)(0,1.5,0)
  \pstThreeDDot[dotscale=2,linecolor=white](0,0,2)
\end{pspicture}

\begin{pspicture}(-2,-1.25)(2,5)
  \AxesThreeD[linecolor=black,linestyle=dashed,arrows=->](30,30,40)
  \psset{linecolor=red,linewidth=2pt,normaleLatitude=90,normaleLongitude=0}
  \CircleThreeD(0,0,0){15}
  \CircleThreeD[linecolor=green,fillstyle=solid,fillcolor=green](0,0,10){15}
  \CircleThreeD[linecolor=blue](0,0,20){15}
\end{pspicture}

\end{document}

more informations in the documentation of the packages

Herbert