[Paraview] colormap for logarithmic quantities

[Kent Eschenberg]

I didn't mean "do your data values make sense"; I'm sure they do.

What I questioned is whether changing the lower bound of the log color scale as you suggest makes sense.

Remember, changing the color scale does not change the data -- the original values, both positive and negative, will be passed through the color lookup table to find their color.

I think with the change you suggest all values from -1e+15 to +1e+15 would get the same color, the one for +1e+15. The colors would only vary between +1+e15 an 9.999e+18. Does that make sense?

If you want to work with the absolute value of your data first pass it through the Calculator and take the absolute value. If needed also set a floor so values don't get too close to 0 where the log blows up.

Kent
Pittsburgh Supercomputing Center

John Doe wrote:
> In semiconductor devices, the net doping is a signed quantity which
> can very exponentially.  It is typical in most device simulation
> packages as it refers to the signed number of donors (positive) and
> acceptors (negative).
> 
> Other candidates for a colormap options would be a "Use log of the
> absolute value", or even "Use asinh scale".
> 
> Regards,
> 
> Juan
> 
> On Tue, Jul 8, 2008 at 1:23 PM, Kent Eschenberg <eschenbe at psc.edu> wrote:
>> That would prevent the error but would it make sense?
>>
>> Kent
>> Pittsburgh Supercomputing Center
>>
>> John Doe wrote:
>>> When I try to view a color map logarithmically, I get the following error:
>>> ERROR: In
>>> /home/berk/Work/ReleaseBuilds/ParaView3/VTK/Common/vtkLookupTable.cxx,
>>> line 120
>>> vtkLookupTable (0x8ff2ae0): Bad table range for log scale: [-1e+15,
>>> 9.999e+18], adjusting to [1, 10]
>>>
>>> Would it be reasonable to request that the log option for the colormap
>>> takes the absolute value of the quantity for which the log is taken?
>>>
>>> Thanks,
>>>
>>> Juan