[Paraview] how does ScalarOpacityUnitDistance affect volume rendering?

[Jeff Mauldin]

Ken is right. 0 is full opacity and 1 is full transparency.

Moreland, Kenneth wrote:
> The correct expression for radiative transform defines light attenuation
> per unit length.  The Scale value allows you to set what that unit length
> is.  The larger the unit length, the further light has to travel to
> attenuate the same amount.
>
> Your description of the behavior seems backward.  If you set the unit
> distance to 0, you should see full opacity.  It means that when light
> travels 0 distance it's attenuated a finite amount.  Thus, any finite
> distance should attenuate all light.  The larger you make the unit
> distance, the more transparent the rendering should become.  This is the
> behavior I get with disk_out_ref.  Are you sure you didn't get it
> backwards?
>
> -Ken
>
>    ****      Kenneth Moreland
>     ***      Sandia National Laboratories
> ***********  
> *** *** ***  email: kmorel at sandia.gov
> **  ***  **  phone: (505) 844-8919
>     ***      web:   http://www.cs.unm.edu/~kmorel
>
>
>
>
> On 8/2/11 11:21 AM, "Jeff Mauldin" <jamauld at sandia.gov> wrote:
>
>   
>> I am working with volume rendering on a particular data set.  I am doing
>> projected tetra volume mapping.  When I bring up the Color Scale Editor
>> dialog (which I have used extensively), there is an entry called "Scale"
>> that I haven't been able to find documentation to.  In playing with the
>> python tracing, I see that it alters a value called
>> ScalarOpacityUnitDistance.  The effect appears to be that setting this
>> parameter to zero causes the rendering to be completely invisible (alpha
>> zero everywhere, presumably) and setting it to 1 causes the rendering to
>> be completely opaque.  I'm guessing it's some kind of multiplier to the
>> opacity value in color transfer function, and possibly some kind of
>> multiplier applying to how much each volume ray segment contributes to
>> the overall opacity of a pixel.  What exactly is this scale value doing
>> (so I can understand what I'm looking at)?
>>
>>
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