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From: Karl Ratzsch <mail.kfr@gmx.net>
Newsgroups: comp.graphics.apps.gnuplot
Subject: Re: Point size default
Date: Tue, 4 Apr 2017 06:02:19 +0200
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Am 03.04.2017 um 15:57 schrieb jacques.Lebourlot@obspm.fr:
> No! Please check carefully the example given (at the end of my
> initial message).
> 
> * This is a 3D plot (splot), not 2D. hence I cannot use objects. 
> * "6" is not the size, but the "point type" (pt), which is an
> empty circle * That circle MUST have exacly a physical size of
> "1.0" => i.e. a radius equal to the unit size of the 3 axes. * It
> must stay in the plane of the screen when I move the 3D object
> with the mouse.
> 
> I know that sizes are terminal dependent. That is the point of
> the question... I had to ajust things by trial and errors, by
> multiplying an "unknown" initial size to get the desired result.
> That size *has* to be defined (or computed) somewhere in the
> code, and passed to the graphical engine at some point, but I am
> not fluent enough in C to find where from the source code.


Ah, sorry. I wasn't aware that both don't work in 3D plots.
Well, you could derive it from the source code, but that's also by
no means a clean solution, plus sounds tricky. What's wrong with
using an empirical value instead?

There are two variables GPVAL_VIEW_ROT_(X/Z) that would allow you to
always have a plotted circle's normal always point in the viewers
direction, but they only update upon "replot", not during mousing.