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Groups > comp.graphics.apps.gnuplot > #3995

Samples, isosamples, and how they affect contour lines

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Contour lines generated by gnuplot can look pretty strange (unexpected) if you do not set both `samples` and `isosamples` to appropriate values. I struggled for hours to find out how exactly `set samples` and `set isosamples` affect the appearance of contour lines, however, all I observed is that setting both to sufficiently large values will generate good-looking contours. Still, I want to understand how exactly this works.

1. What is the difference between `set samples` and `set isosamples` in the context of contour lines?
2. How does `set samples` affect the generation of contour lines?
3. How does `set isosamples` affect the generation of contour lines?

For example, consider the following simple case:

    unset surface
    set contour
    set cntrparam levels discrete 10, 20
    set samples 250, 2
    set isosamples 2, 250
    set view map
    splot x**2 + y**2

To generate correct contour lines, it appears you need to set the first parameter of `samples` and the second parameter of `isosamples` to sufficiently large values. However, setting the second parameter of `samples` and the first parameter of `isosamples` to the smallest possible value does no harm. This is not exactly intuitive. So how does this work?

I note that I asked this question before on Stack Overflow, but got no answers.

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Samples, isosamples, and how they affect contour lines nawridlz@gmail.com - 2018-07-11 00:02 -0700
  Re: Samples, isosamples, and how they affect contour lines Karl Ratzsch <mail.kfr@gmx.net> - 2018-07-11 11:26 +0200
    Re: Samples, isosamples, and how they affect contour lines nawridlz@gmail.com - 2018-07-11 22:39 -0700
      Re: Samples, isosamples, and how they affect contour lines Karl Ratzsch <mail.kfr@gmx.net> - 2018-07-12 08:08 +0200
        Re: Samples, isosamples, and how they affect contour lines nawridlz@gmail.com - 2018-07-11 23:50 -0700
          Re: Samples, isosamples, and how they affect contour lines Karl Ratzsch <mail.kfr@gmx.net> - 2018-07-12 17:18 +0200
            Re: Samples, isosamples, and how they affect contour lines nawridlz@gmail.com - 2018-07-13 00:22 -0700
              Re: Samples, isosamples, and how they affect contour lines Karl Ratzsch <mail.kfr@gmx.net> - 2018-07-13 12:39 +0200
  Re: Samples, isosamples, and how they affect contour lines Karl Ratzsch <mail.kfr@gmx.net> - 2018-07-13 09:53 +0200

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