[vtkusers] Point rendering : how to filter values with a vtkLookupTable

[David.Pont at ForestResearch.co.nz]

Hi Aurélien,
   The code fragment below constructs a greyscale lookuptable with 5
colors. After the call to Build one color is changed so that alpha is 0.
Data values mapped into this color in the lookuptable will be transparent.

      vtkLookupTable *lut1 = vtkLookupTable::New();
            lut1->SetRange( 0, 0.5 );
            lut1->SetNumberOfColors( 5 );
            lut1->SetHueRange( 0, 0 );
            lut1->SetSaturationRange( 0, 0 );
            lut1->SetValueRange( 0, 1 );
            lut1->Build();
            lut1->SetTableValue( 1, 0, 0, 0, 0 );     // make one band
disappear, note: rgb values not important

      vtkPolyDataMapper *pdm1 = vtkPolyDataMapper::New();
            pdm1->SetInput( clpd1->GetOutput() );
            pdm1->SetScalarRange( 0, 0.5 );
            pdm1->SetLookupTable( lut1 );
            pdm1->ScalarVisibilityOn();

You should be able to use appropriate values for SetRange,
SetNumberOfColors, SetTableValue and SetScalarRange to hide parts of your
dataset. This worked for me on polydata surfaces, I am not sure about
rendering points, but I would expect it to work.

  bon chance
     Dave Pont



                                                                                                               
                      REGAT-BARREL                                                                             
                      Aurélien                 To:       VTK <vtkusers at vtk.org>                                
                      <arbvtk at yahoo.fr>        cc:                                                             
                      Sent by:                 Subject:  [vtkusers] Point rendering : how to filter values     
                      vtkusers-admin at vt         with a vtkLookupTable                                          
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                      05/02/2004 03:24                                                                         
                                                                                                               
                                                                                                               




Hello,
I have a vtkStructuredPoints which contains some interesting values but
also some "empty" values (=0) that are viewed in black, all around the
interesting object which is composed by points from values 1 to 255.  I
would like to not see points with value zero, in order to "free" the object
inside.  I tried to play with a vtkLookupTable in order to assign a null
alpha value to black points (=0) but it didn't work. The mapper seems to
ignore my changes to its lookuptable.  Here is an example. How can I filter
black values without modifying my vtkStructuredPoints.

package require vtk
package require vtkinteraction
package require vtktesting
vtkMath math
# 20x10x10 points
set numberOfInputPoints 2000
vtkUnsignedCharArray scalars
for {set i 0} {$i < $numberOfInputPoints} {incr i 1} {
    scalars InsertNextTuple1 [math Random 0 255]
}
vtkStructuredPoints cloud
    cloud SetDimensions 20 10 10
    cloud SetOrigin 0 0 0
    cloud SetSpacing 1 1 1
    [cloud GetPointData] SetScalars scalars
vtkDataSetMapper mapper
    mapper SetInput cloud
    mapper SetScalarRange 0 256
vtkActor actor
    actor SetMapper mapper
vtkRenderer ren
    ren AddActor actor
    ren SetBackground 0 0 0

vtkRenderWindow renWin
renWin AddRenderer ren
vtkRenderWindowInteractor iren
iren SetRenderWindow renWin
renWin SetSize 500 500
renWin Render
iren Start
wm withdraw .

Later, I would like to create a slider that allows the user to filter
viewed values from 0 to 255. How to do that ?
I attach a screenshot that shows my problem. I have a 3D object but I can't
see it well. Black values are undesirable.

Thanks.

Aurélien


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