# [pstricks] Points and vectors on a sphere with pst-3dplot

Felix Suwald felix.suwald at gmail.com
Wed Jul 5 11:06:31 CEST 2006

Hello

I would like to draw a sphere with the
invisible axis dashed, and the visible
part of the axis pointing outwards as an
arrow. The problem is, that the outer axis
lines seem not to start at the surface
of the sphere, but somewhere below,
when I say that the start point is at a
distance equal to the radius of the sphere.
I tried with and without spherical coordinates.
What am I missing? What is wrong with
the radius of the sphere? I am confused,
because:
I tried the package pst-vue3d before,
and there it seems to work. I could draw
lines starting on the surface of the sphere
by stating the radius of the sphere as distance.
I then gave up pst-vue3d because when I
draw a tangential plane on the sphere
(using unit vectors e_theta and e_phi)
and a parallel plane above the tangential one,
the unit vectors were not parallel anymore,
and that confuses a lot. Is there a way to
switch off the perspective view in pst-vue3d?

Here my basic example with the strange
axis behaviour.

%%%%%% A sphere %%%%%%
\documentclass[a4paper]{article}
\usepackage{pstricks}
\usepackage{pst-3dplot}
\begin{document}
\begin{figure}
\begin{pspicture}(-10,15)(0,0)
\pstThreeDCoor[xMin=0,yMin=0,zMin=0]
\pstThreeDSphere[linewidth=0.5pt](0,0,0){3}
\psset{SphericalCoor}
\pstThreeDNode(3,0,0){x_base}
\pstThreeDNode(6,0,0){x_end}
\psline[linecolor=black]{->}(x_base)(x_end)
% uhh, where does this axis start?
\pstThreeDLine[linecolor=green]{->}(3,0,90)(6,0,90)
\end{pspicture}
\end{figure}
\end{document}

Regards, Felix
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