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<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
<p class="MsoNormal"><span style="color:#1F497D"><o:p> </o:p></span></p>
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<p class="MsoNormal"><b><span lang="EN-US" style="mso-fareast-language:EN-GB">From:</span></b><span lang="EN-US" style="mso-fareast-language:EN-GB"> Bertram Sabrowsky-Hirsch
<br>
<b>Sent:</b> 29 March 2018 13:29<br>
<b>To:</b> 'vtkusers@vtk.org' <vtkusers@vtk.org><br>
<b>Subject:</b> vtkProjectedTetrahedraMapper to map one component only<o:p></o:p></span></p>
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<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Hi everyone,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I have troubles implementing a similar feature found in Paraview: I do have a vtkUnstructuredGrid where the PointData contains 4 different (Float) Arrays (e.g. “Pressure”, “Velocity”, …).
<br>
One of those Arrays has 3 components and I want to let the user decide which one of the components is used for the color mapping.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">What I do:<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoListParagraph" style="text-indent:-18.0pt;mso-list:l0 level1 lfo2"><![if !supportLists]><span style="mso-list:Ignore">-<span style="font:7.0pt "Times New Roman"">
</span></span><![endif]>Set the active Attribute of the grid to select the array that is visualized:<o:p></o:p></p>
<p class="MsoListParagraph"><span style="font-size:9.5pt;font-family:Consolas;color:black">grid->SetActiveAttribute(grid->GetInformation(),
</span><span style="font-size:9.5pt;font-family:Consolas;color:darkcyan">vtkDataObject</span><span style="font-size:9.5pt;font-family:Consolas;color:black">::</span><span style="font-size:9.5pt;font-family:Consolas;color:#314F4F">FIELD_ASSOCIATION_POINTS</span><span style="font-size:9.5pt;font-family:Consolas;color:black">,
“Velocity”, </span><span style="font-size:9.5pt;font-family:Consolas;color:darkcyan">vtkDataSetAttributes</span><span style="font-size:9.5pt;font-family:Consolas;color:black">::</span><span style="font-size:9.5pt;font-family:Consolas;color:#314F4F">SCALARS</span><span style="font-size:9.5pt;font-family:Consolas;color:black">);</span>
<o:p></o:p></p>
<p class="MsoListParagraph"><o:p> </o:p></p>
<p class="MsoListParagraph" style="text-indent:-18.0pt;mso-list:l0 level1 lfo2"><![if !supportLists]><span style="mso-list:Ignore">-<span style="font:7.0pt "Times New Roman"">
</span></span><![endif]>Use a vtkDataSetTriangleFilter and connect it with a vtkProjectedTetrahedraMapper and finally set the mapper to a vtkVolume that is rendered<o:p></o:p></p>
<p class="MsoListParagraph"><o:p> </o:p></p>
<p class="MsoListParagraph" style="text-indent:-18.0pt;mso-list:l0 level1 lfo2"><![if !supportLists]><span style="mso-list:Ignore">-<span style="font:7.0pt "Times New Roman"">
</span></span><![endif]>Set a custom <span style="font-size:9.5pt;font-family:Consolas;color:darkcyan">
vtkColorTransferFunction </span>in the volumes properties to map the scalar values to colors<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Now, for single component arrays, this works just fine. <o:p>
</o:p></p>
<p class="MsoNormal">For arrays with multiple components - as I understand it - this will always use the magnitude of the components to map the scalar values.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal"><span style="font-size:9.5pt;font-family:Consolas;color:darkcyan">vtkColorTransferFunction
</span>does offer to<span style="font-size:9.5pt;font-family:Consolas;color:darkcyan">
</span>set the vector components using the functions (<span style="font-size:9.5pt;font-family:Consolas;color:black">SetVectorModeToComponent(), SetVectorComponent(idx), SetVectorSize(1))
</span>and I tried this,<o:p></o:p></p>
<p class="MsoNormal">however, after inspecting the source code of vtkProjectedTetrahedraMapper I think that this feature is ignored by the mapper. Also, I didn’t find any way to adjust the grid in a way that a specific component is used (I figured there might
be something like SetActiveComponent as it exists for attributes with SetActiveAttribute).<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">I also looked into using vtkArrayCalculator and vtkExtractBlock but I don’t understand the VTK data concept well enough to find a solution on my own.<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Is there a simple way to get the vtkProjectedTetrahedraMapper to use one specific component?<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Thanks in advance,<o:p></o:p></p>
<p class="MsoNormal"><o:p> </o:p></p>
<p class="MsoNormal">Kind regards,<o:p></o:p></p>
<p class="MsoNormal">Bertram<o:p></o:p></p>
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