[Paraview] how does ScalarOpacityUnitDistance affect volume rendering?

[Moreland, Kenneth]

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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