contourlines problem

contourlines problem

Post by crawford richa » Fri, 13 Dec 1996 04:00:00

> we have encountered the following problem when plotting contourlines:

> Using

>   set param
>   set nosurface
>   set view 0,0
>   set contour
>   set cntrparam levels discrete 0.05,0.1,0.5,1.0,1.5
>   set cntrparam bspline   #optional
>   splot 'wave__.d' w l

>   # see end of the text for file  'wave__.d'

> we find that the contourlines are not symmetric with
> respect to the horizontal x-axis, although
> the z numbers in 'wave__.d' are the same for positive and
> negative y value.
> (This applies to unix version 3.5 (pre 3.6)
>         patchlevel beta 273
> and also to
>         patchlevel beta 322
> under Linux and under HP-UX)

> Has anyone any idea why this goes wrong ?

> [data file deleted]

I've noticed this in the past.  I believe that the algorithm isn't
symmetric, in that if it passes through the data top to bottom, it
gets a different result than if it passes the other way.

I can imagine an algorithm that behaves this way, but I've not had
the time or patience to wade through the code to see how gnuplot's
contouring works, if it's relatively easily fixable or if it needs
a wholesale rewrite.

I know this doesn't really help :-(


1. contourlines in 3d field


i've got a 3d-field of data, x and y are
coordinates, z is an amplitude varying between -1
and 1. I want to have a projection of the data in
the x,y-square with lines corresponding to z-values
1, 0.9, 0.8, 0.7 ... -0.8, -0.9, -1. How can i plot
such isolines with gnuplot

Please mail me,
 thanks in advance

 Thorsten Kamps

***                Thorsten Kamps                     ***
***     DESY-IFH / Platanenallee 6 / 15738 Zeuthen    ***
*** vox +49-(0)33762-77-202 / fax +49-(0)33762-77-330 ***


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