• john gehman

    john gehman - 2001-05-23

    I'm having issues with attempts to contour my 3D data.

    I'm running gnuplot 3.7 patch level 1 on Redhat6.2.

    Briefly, I 'set contour base', 'set' a number of contour
    options like discrete levels and cntrparam bspline, then
    'set dgrid3d 100,10,4', 'set term table', 'set out file',
    'splot <data>' then set terminal to either X11 or latex,
    set all the format options, and 'plot file'

    This has worked fine for me in the past. I am now trying
    to process some data that is (along x) 561 points between
    0 and 1, and (along y) 19 points between 0.01 and 0.1 There
    is a z value for every x,y pair. Most of the detail that I
    want to contour is found at x<0.05 (415 of the 561 points)
    and at y = 0.01, 0.015, and somewhat at 0.02. However, using
    the previously successful approach described above, I get
    contours with x component much larger, but roughly parallel,
    to where they should be.

    If I view the surface without dgrid3d or contour, it looks
    just as I would expect. Is there some known limitation of
    gnuplot to deal with extreme slopes, or perhaps a problem
    with using such large numbers with dgrid3d?

    Any assistance would be immensely appreciated. I've been
    struggling with this for days now.

    • Hans-Bernhard Broeker

      You shouldn't be using dgrid3d in this situation. You don't need it, as your datafile already has the 'grid structure' needed by contouring. At least implicitly, it does. By your use of 'dgrid3d', you're effectively killing all detail of the original input data below 1/100 of the total xrange --- for the case you describe, that's over 80% of the original level of detail.

      If gnuplot complains it "cannot contour non-grid data",  that's because the layout of the datafile isn't following the rules, yet. Inserting a few linebreaks would fix that in an instant, and get you a better plot than dgrid3d to a fixed-size grid.


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