[vtkusers] coloring an isosurface with a second variable

[Charles Boivin]

Hi John,

Well, this perhaps will show my ignorance of VTK as I am a relative
newbie, but as far as I know, point data *is* field data. If you look at
the vtkPointData documentation, you will see that that class is derived
from vtkFieldData. 

By the way, a call to vtkPolyData::GetPointData() (like you have in
your example code below) returns a pointer to a vtkPointData object, so
I think using vtkPolyDataMapper::SelectColorArray() should still work.
Make sure that you have called
vtkPolyDataMapper::SetScalarModeToUsePointFieldData() first. 

So, as far as I understand it, this should work (it does for me,
although I am not using the vtkXMLStructuredGridReader). Hope this
helps!

Charles

>>> "John Clyne" <clyne at ucar.edu> 10/29/04 12:23pm >>>
Charles, this shows my ignorance of vtk, but it looks like
SelectColorArray
can be used when you have "Field" data. the vtkXMLStructureGridReader
loads
the scalar data as "Point" data. I don't really understand the
difference
between Point and Field data, nor how you might convert one to the
other.
Any insight here?

Thanks for your quick response, Charlse.

cheers - jc


----- Original Message ----- 
From: "Charles Boivin" <Charles.Boivin at rwdiwest.com>
To: <clyne at ucar.edu>; <vtkusers at vtk.org>
Sent: Friday, October 29, 2004 11:31 AM
Subject: Re: [vtkusers] coloring an isosurface with a second variable


> Hi John,
> 
> I have been using vtkPolyDataMapper::SelectColorArray() to color an
> isosurface with another variable. Seems to work pretty well for me.
> 
> Charles
> 
> >>> "John Clyne" <clyne at ucar.edu> 10/29/04 11:16am >>>
> I'm trying to do what I would think would be a trivial operation but
I
> can't for for the life of me figure out how to do in vtk. I have an
XML
> data
> file (.vts) that contains two scalar variables (temperature and
> humidity).
> I'd like to generate an isosurface of one and color it with the
other.
> Selecting the field to isosurface is easy enough:
> 
> vtkXMLStructuredGridReader reader
>     reader SetFileName $Datafile
>     reader Update
>     [[reader GetOutput] GetPointData] SetActiveScalars "humidity"
> 
> This selects the appropriate field for the isosurfacer, and if I do
a
> 
> puts "[[mapper GetInput] Print"
> 
> 
> I see both the temperature and humidity arrays named as "Point
Data",
> but
> now I have no idea how to tell the mapper to map the temperature
field
> through the lookup table to assign color to the resulting geometry
> coming
> out of the vtkContour.
> 
> Any pointers would be greatly appreciated.
> 
> thanks!
> 
> 
> John Clyne (clyne at ncar.ucar.edu)
> National Center for Atmospheric Research
> 1850 Table Mesa Dr. Boulder, CO 80303 USA
> 1.303.497.1236
> 
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