Graphics, Figures & Tables ⇒ [pstricks] psRandom - distance to clipping object

[mushroom20]

Dear all,

I would like to draw a certain amount of dots or circles randomly arranged in an ellipse. So I used the command \psRandom from the package pstricks-add and got the following result

Code: Select all

\documentclass[a4paper]{scrbook}

\usepackage[ngerman]{babel}
\usepackage{pstricks-add}

\begin{document}
  \begin{pspicture}(4,4)
  \definecolor{orange}{cmyk}{0,0.61,0.87,0.001}
  \psgrid[gridcolor=orange, gridwidth=0.5pt,subgridwidth=0.1pt, subgridcolor=orange,subgriddiv=10]
  \psRandom[dotsize=0.5mm, randomPoints=500](1.9,1)(2.9,2){%
  \psellipse[linestyle=none](2.5,1.5)(0.5,0.3)}
  \end{pspicture}
\end{document}

Unfortunately, the dots at the edge of the ellipse are cut, because \psRandom arranges the dots in a rectangular object. Is there a possibility to arrange the dots with a certain distance to the edge of the ellipse, so that all dots are completely within the ellipse and not cut anymore?

I posted the issue also in http://golatex.de/pstricks-psrandom-abs ... 18455.html in german.

Thanks
Markus

[Stefan Kottwitz]

Hi Markus,

welcome to the forum!

Very good!

• You made an excellent minimal example.
• You linked the cross-post for information.

So I really want to answer even though I'm not so familiar with PSTricks, but with TikZ. So here is a TikZ solution - you can adapt it to PSTricks of cause.

Truly random points can look bad: some dense clusters, some big gaps. So I would do a small trick: distribute the points equally along the x axis, and make the y value random. Using the math function for an ellipse, you can plot a function in x with the value of the y height multiplied with a random value between -1 and 1. Make it a bit smaller to stay inside the ellipse.

Code: Select all

\documentclass[tikz, border=10pt]{standalone}
\usepackage{pgfplots}
\pgfplotsset{compat=1.11}
\pgfmathsetseed{5}
\begin{document}
\begin{tikzpicture}
  \begin{axis} [
      hide axis,
      axis equal
    ]
    \addplot [only marks, samples=120, domain=-3.9:3.9]
      ({ x },{rand * (sqrt( 2^2 * (1 - \x^2/(4^2) ) - 0.4)} );
    \draw (0,0) ellipse [x radius=4, y radius=2];
  \end{axis}
\end{tikzpicture}
\end{document}

random-circles.png (17.33 KiB) Viewed 5373 times

Of course you could also make a loop and make the x value random, the way is the same. I can show that too, if desired. I just like that a bit equally distributed still random looking plot.

Stefan

[CrazyHorse]

Code: Select all

\documentclass[pstricks]{standalone}
\usepackage{pst-plot}
\begin{document}
	
\begin{pspicture}[showgrid](-4.3,-2.3)(4,2.2)
\psplot[plotstyle=dots,algebraic,plotpoints=200]{-3.9}{3.9}{Rand*(sqrt(4-x^2/4)-0.1)}
\psplot[plotstyle=dots,algebraic,plotpoints=200]{-3.9}{3.9}{Rand*(-sqrt(4-x^2/4)+0.1)}
\psellipse(0,0)(4,2)
\end{pspicture}
\end{document}

Bildschirmfoto vom 2017-01-19 17-45-12.png (38.71 KiB) Viewed 4573 times

[mushroom20]

Thanks, Crazyhorse

with your hint, it's also working now in my case.