[vtkusers] Coloring PolyDatas depending on various (externally computed) values

[Arnaud GELAS]

On 10/25/2010 08:42 PM, David Doria wrote:
> On Mon, Oct 25, 2010 at 6:04 PM, Arnaud GELAS 
> <arnaud_gelas at hms.harvard.edu <mailto:arnaud_gelas at hms.harvard.edu>> 
> wrote:
>
>     Hi all,
>
>     I would like to color some PolyData depending on different kind of
>     information/data.
>
>     For each polydata, I have an initial color (chosen by the user),
>     and N values (volumes, surface, etc...), and I would like to
>     efficiently switch from the chosen color, to a color which
>     represents the value.
>
>         * To store these values (computed externally), which
>           vtkPolyData's data container should I use?
>           Note that I have about 10k meshes with ~500 triangles, and
>           about 10 computed values, and I'd like each polydata to
>           store its N value.
>               o vtkFieldData?
>               o vtkCellData?
>               o vtkPointData?
>         * How can I efficiently switch from rendering with colors
>           which would represent one value (e.g. volume), to colors
>           which would represent another one (e.g. surface), then to
>           the original color (the one chosen by the user)?
>
>
>     Thanks in advance,
>     Arnaud
>
>
> Arnaud,
>
> The choice of Field,Cell, or Point data depends strictly on where 
> these colors are defined. Are they defined at the points of the meshes 
> or the triangles? If its at the points (i.e. each point has a color), 
> you'll want to use PointData. If it's at the triangles (i.e. each 
> triangle has a color) you want to use CellData. FieldData is for 
> "global information" about the whole data set typically, so you 
> wouldn't want to use that here.
>
> Lets go forward assuming that the colors are defined on the points. 
> You would want to do this
>
> vtkUnsignedCharArray* colors1 = vtkUnsignedCharArray::New();
> colors1->SetName("colors1");
> ... fill the colors array
>
> vtkUnsignedCharArray* colors2 = vtkUnsignedCharArray::New();
> colors2->SetName("colors2");
> ... fill the colors array
>
> polydata->GetPointData()->AddArray(colors1);
> polydata->GetPointData()->AddArray(colors2);
>
> Now here is the key. To select which one is used, use this:
>
> polydata->GetPointData()->SetActiveScalars("colors1");
>
> I think that is what you were looking for? Give it a try and let us 
> know if it wasn't.
>
> David

David,

It works fine with PointData and CellData; however I could not figure 
out how to proceed with FieldData (There is no method SetActive at this 
level in the hierarchy :-/, and my values are attributes to one mesh 
(constant for a single mesh).
Is there a way to proceed with vtkFieldData?

---

If not, I can use CellData instead. In this case, I can switch from 
active scalar array to original mesh colors by setting it to one that 
does not belong to the mesh:

polydata->GetCellData->SetActiveScalars( "" );

Is there a better way to proceed?

Thanks,
Arnaud


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