[vtkusers] Re: LookupTable and ScalarBar

[Steve Joyce]

Hi,

For a log scale to be displayed correctly in a scalar bar you need to use vtkLogLookupTable.
The vtkScalarBarActor class does not treat this the same as vtkLookupTable with SetScaleToLog10(), even though it should.
To create a custom scale you can use a vtkColorTransferFunction, which vtkScalarBarActor will also accept, although it doesn't always handle it very well.

It might be nice to have a scalar bar class that you just passed a set of labels and a set of colours to and it just displayed them, perhaps with options to control the width of each colour band and the positioning of the labels.
That would allow any type of non-linear scale to be displayed.

Steve

>>> vtkusers-request at vtk.org 04/08/2004 17:00:08 >>>
 
                       I am trying to plot (pressure) values from 10^ -7 to 10^ +7 in VTK. But most of the values are centered around 10^ +5.  I want the full range of colors in the scalar bar between 10^+4 and 10^ +6. Is there a way to do this in VTK?? I cannot set range between 10^ +4 and 10^+6, because I want to plot the other values as well.
 
                      In other words, I want to map particular values(of pressure) to particular colors on the scalar bar. Can I build a lookuptable which can do this??
 
                     I tried using the log scale. But all it does is it converts the colors into logarthmic fashion keeping the values linear.I would have expected the labels to progress logorithmically over the range so that I can clearly see the colors in the map. Can I get this effect without having to write my own lookup table/scalar bar?

Thanking you,
Nikhil Butala
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