[vtkusers] Adding chars to 3D char array in python or how to add colors to array?

[David Doria]

On Mon, Dec 21, 2009 at 2:56 PM, David Gobbi <david.gobbi at gmail.com> wrote:
> On Mon, Dec 21, 2009 at 12:32 PM,  <lynx.abraxas at freenet.de> wrote:
>> On 21/12/09 01:42:22, David Gobbi wrote:
>>> Hi Lynx,
>>>
>>> Use SetTuple3(), the doubles are converted to the array type before
>>> they are stored.
>>
>> Thanks David G. for this hint. It works nicely with this.
>>
>>> Also a note about this example: it's best to use SetScalars() to add
>>> colors to the data, so that you don't have to do anything special in
>>> order to display them.  That example is misleading, the array name
>>> "Colors" doesn't have any special meaning in VTK.
>>>
>>> smoothed_polys.GetPointData().SetScalars(colors)
>>
>> Hm, I'm not getting this. Isn't my colors actually a vector? If I use
>> smoothed_polys.GetPointData().SetScalars(colors) instead of
>> smoothed_polys.GetPointData().AddArray(colors)
>
> VTK Scalars are allowed to have multiple components, so that is not a problem.
>
>> I get an error in vtkDataArray.cxx line 470:
>> vtkUnsignedCharArray ...: The number of components do not match the number requested: 3 != 1
>
> Before you add any tuples, you have to set the number of components in
> your array:
>
> colors.SetNumberOfComponents(3)
>
>   David
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>

Here is another common point of confusions - you can see how most
people are confused by "scalars" rather than "colors" especially since
colors typically have 3 components (RGB), which is not a scalar! :)
The SetPointColors function could go ahead and SetNumberOfComponents
to 3 as well as do whatever else may be necessary
(SetScalarModeToUseXXX(); or something).

I will not attempt to fight for adding these functions (as like you
said they can have many repercussions and may not make sense for all
users), but a lack of "easy to understand" API certainly calls for a
good set of examples ;) Lynx, now that David G got you up and running
with this problem, you've just self-volunteered for adding examples
demonstrating this :)

Thanks,

David