[Numpy-discussion] constant shaded triangle mesh in mayavi2

[Robert Kern]

On Thu, Sep 30, 2010 at 16:26, Geoffrey Irving <irving at naml.us> wrote:
> On Fri, Oct 1, 2010 at 10:18 AM, Robert Kern <robert.kern at gmail.com> wrote:
>> On Thu, Sep 30, 2010 at 16:00, Geoffrey Irving <irving at naml.us> wrote:
>>> On Fri, Oct 1, 2010 at 9:38 AM, Robert Kern <robert.kern at gmail.com> wrote:
>>>> On Thu, Sep 30, 2010 at 15:30, Geoffrey Irving <irving at naml.us> wrote:
>>>>> Hello,
>>>>>
>>>>> I'm not sure where the correct place to ask questions about Mayavi, so
>>>>> feel free to redirect me elsewhere.
>>>>
>>>> https://mail.enthought.com/mailman/listinfo/enthought-dev
>>>>
>>>>> I have a triangle mesh with a bunch of data on each face.  The only
>>>>> color-relevant argument to triangular_mesh I know about is scalars,
>>>>> which is one value per vertex.  Is there a way to set color per
>>>>> triangle, ideally with control over rgb separately so I can visualize
>>>>> three different fields at once?
>>>>
>>>> Pretty difficult, unfortunately. The only way I have found is to
>>>> assign UV texture coordinates to the vertices and slap on a texture.
>>>> Assigning the UV coordinates is usually not easy.
>>>
>>> Is this a limitation in VTK, TVTK, or the Mayavi python code?  The VTK
>>> documentation seems to imply it supports cell data on polygon meshes
>>> (though I don't know how one would set them):
>>>
>>>    http://www.vtk.org/doc/release/5.6/html/a01445.html
>>>    "Point and cell attribute values (e.g., scalars, vectors, etc.)
>>> also are represented"
>>>
>>> I'm happy to hack TVTK or Mayavi (in order of happiness) to support
>>> cell data if VTK supports it.
>>
>> It's a VTK restriction. You can store whatever data you like on the on
>> the vertices or cells. There is no mapper (that I am aware of) that
>> takes that data and interprets them as RGB values on a per-vertex or
>> per-cell basis. There are mappers that turn scalar vertex and cell
>> attribute values into colors through a colormap table, but that's not
>> what you are asking for.
>
> Visualizing a signle cell scalar field is still quite useful (the data
> doesn't correspond to color).  In other words, the per-cell part of
> the question is more important than than the RGB part.  Is there a
> current way to set a cell attribute value on a Mayavi triangular_mesh?

You're better off not using triangular_mesh(). Construct the mesh
separately from the surface.

  s = mlab.pipeline.triangular_mesh_source(x,y,z,triangles)
  s.data.cell_data.scalars = .... # Your data here.
  surf = mlab.pipeline.surface(s)
  surf.contours.filled_contours = True

-- 
Robert Kern

"I have come to believe that the whole world is an enigma, a harmless
enigma that is made terrible by our own mad attempt to interpret it as
though it had an underlying truth."
  -- Umberto Eco