[Octave-bug-tracker] [bug #48552] isonormals should point towards lower values for Matlab compatibility

[Markus Mützel]

URL:
  <http://savannah.gnu.org/bugs/?48552>

                 Summary: isonormals should point towards lower values for
Matlab compatibility
                 Project: GNU Octave
            Submitted by: mmuetzel
            Submitted on: Mon 18 Jul 2016 11:50:49 AM GMT
                Category: Plotting
                Severity: 3 - Normal
                Priority: 5 - Normal
              Item Group: Matlab Compatibility
                  Status: None
             Assigned to: None
         Originator Name: 
        Originator Email: 
             Open/Closed: Open
         Discussion Lock: Any
                 Release: dev
        Operating System: Any

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Details:

As can be seen in [1], the vertex normals as calculated with "isonormals"
point in the opposite direction as compared to Matlab.
See also:

[x,y,z] = meshgrid (-2:0.2:2, -2:0.2:2, -2:0.2:2);
val = x.^2 + y.^2 + z.^2;
[f,vert] = isosurface (x, y, z, val, 1);
vn = isonormals (x, y, z, val, vert);

dirn = vn ./ vert;
all (dirn(isfinite (dirn)) <= 0) % true in Matlab
all (dirn(isfinite (dirn)) >= 0) % true in Octave


I will attach a patch with a change to get the same result in Matlab and in
Octave as soon as I get a bug number.

[1] http://josoansi.de/octave_plot_compare/compare_plot_demos_04.html#light_08




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