# [pstricks] x- and yunit behavior in 3D pictures

Leon Free leon.free at free.fr
Tue Jan 5 13:50:32 CET 2016

Hi Doris
What you say makes sense: the fixed points of the (x,y,z)->(x,.5y,z)
mapping are vectors with y=0. And obvioulsy, the plane in my example
is entirely characterized by such vectors (normal and origin).

But I am not sure this is the mapping that operates on the rendering
of 3D vectors after changing the yunit value (although that may be
true for (x,y) vectors). For instance, I get the same (distorted)
result as in my initial example when using a plane that goes through
(1,1,0) with normal (1,2,1)..

Le mardi 05 janv. 2016 à 09:54:14 (+0100), Doris Behrendt a écrit :
> Hi Leon,
>
> change the position of the plane, then you can understand better.
> Since you put the planes at (0,0,0) — which is mapped on itself by the linear mapping (x,y,z)->(x,.5y,z) — there is no effect of the mapping in your example. Try mine, where I put the planes at (1,0,0).
> Hope this helps.
>
>
> Doris
>
> \documentclass{article}
> \usepackage{pst-solides3d,pstricks}
>
> \begin{document}
> %1st picture with defaults for x- and yunit
> \begin{minipage}[t]{.5\linewidth}
>       \begin{pspicture}
>     \psset{viewpoint=40 25 15 rtp2xyz,Decran=60}
>       \axesIIID(-2,-2,-2)(2,2,2)
>        \psSolid[object=plan,%
>        definition=normalpoint,%
>        args={1 0 0 [0 0 1]},
>        fillcolor=blue,%
>        opacity=.2,%
>        base = -2 3 -1 3,%
>        planmarks]
> \end{pspicture}
> \end{minipage}
> %
> \hspace*{2cm}
> %
> \begin{minipage}[t]{.5\linewidth}
> %2nd picture : changed yunit value
>      \begin{pspicture}
>      \psset{xunit=1cm,yunit=.5cm,viewpoint=40 25 15 rtp2xyz,Decran=60}
>        \axesIIID(-2,-2,-2)(2,2,2)
>        \psSolid[object=plan,%
>        definition=normalpoint,%
>        args={1 0 0 [0 0 1]},
>        fillcolor=blue,%
>        opacity=.2,%
>        base = -2 3 -1 3,%
> planmarks]
> \end{pspicture}
> \end{minipage}
>
> \end{document}
>
>
> > On 05 Jan 2016, at 08:05, leon.free at free.fr wrote:
> >
> > Hi,
> >
> > In 2D drawing, I understand that the expected behavior of changing the
> > xunit/yunit parameter is to modify the aspect ratio, resulting in a
> > figure where all objects are rescaled accordingly to this ratio. In 3D
> > figures, it is unclear what changes occur after changing the values of
> > xunit and yunit.
> >
> > In the following example, both pictures result from identical
> > pstricks/pst-solides3d macros, excepted that the first uses the
> > defaults for x- and yunit, while in the second one, yunit is set to
> > 0.5cm. It appears that the size and the perspective rendering of the
> > axes are modified accordingly, but the \psSolid plan object is not
> > (neither in size nor in perspective).
> >
> >
> > \documentclass{article}
> > \usepackage{pst-solides3d,pstricks}
> >
> > \begin{document}
> > %1st picture with defaults for x- and yunit
> > \begin{minipage}[t]{.5\linewidth}
> >       \begin{pspicture}
> >     \psset{viewpoint=40 25 15 rtp2xyz,Decran=60}
> >       \axesIIID(0,0,0)(2,2,2)
> >        \psSolid[object=plan,%
> >        definition=normalpoint,%
> >        args={0 0 0 [0 0 1]},
> >        fillcolor=blue,%
> >        opacity=.2,%
> >        base = -2 3 -1 3,%
> >        planmarks]
> > \end{pspicture}
> > \end{minipage}
> > %
> > \hspace*{2cm}
> > %
> > \begin{minipage}[t]{.5\linewidth}
> > %2nd picture : changed yunit value
> >      \begin{pspicture}
> >      \psset{xunit=1cm,yunit=.5cm,viewpoint=40 25 15 rtp2xyz,Decran=60}
> >        \axesIIID(0,0,0)(2,2,2)
> >        \psSolid[object=plan,%
> >        definition=normalpoint,%
> >        args={0 0 0 [0 0 1]},
> >        fillcolor=blue,%
> >        opacity=.2,%
> >        base = -2 3 -1 3,%
> >        planmarks]
> > \end{pspicture}
> > \end{minipage}
> >
> > \end{document}
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