Groups > comp.graphics.apps.gnuplot > #4005

Re: Samples, isosamples, and how they affect contour lines

From	Karl Ratzsch <mail.kfr@gmx.net>
Newsgroups	comp.graphics.apps.gnuplot
Subject	Re: Samples, isosamples, and how they affect contour lines
Date	2018-07-12 08:08 +0200
Organization	solani.org
Message-ID	<pi6r9e$cjn$1@solani.org> (permalink)
References	<884eb2ab-a118-41a9-aaa1-bfcdd71f0d0e@googlegroups.com> <pi4igh$v3p$1@solani.org> <31e8c304-ae02-4814-b3f3-48c06a77dded@googlegroups.com>

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Am 12.07.2018 um 07:39 schrieb nawridlz@gmail.com:
> I'm sorry, I still have no idea what's going on here. Consider the following example:
> 
>     set samples 6
>     set isosamples 500
>     set table $surface
>     splot x ** 2 + y ** 2
>     unset table
>     set contour
>     set cntrparam levels discrete 80
>     set view map
>     splot $surface
> 
> 1. Why is there a smooth curve in the interval [-10, -6]?
> 2. Why is there a straight line in the interval [-6, -2]?
> 3. Why are there no points at all in the interval [-2, 2]?
> 

gnuplot takes the grid values in x-direction, and adds an interpolated
contour point wherever the connection between these two points crosses
the y-grid. (afterwards it does the same in the other direction, and
sorts the interpolated points into a closed contour line)

The 2 lines between -2 and 2 are horizontal, so they don't cross the
y-grid at all.

I mean, you cannot expect a nice-looking contour on a data grid that
only has six values in one direction, right? You need a grid with
similar density in BOTH directions.

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Thread

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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