The last few days we had quite a mix of heavy rain and sunshine in austria and as consequence you could observe quite a lot of rainbows.
So I thought lets build one in Houdini. I managed to create a volume with density and Cd assigned but now I have some questions.
How can I make a volume light emissive ?? The default volume is just light absorbing ..
How can I get a Viewport visualization of my volume with the colors ?
As you can see in the attached file, the viewport looks quite weird. If the volume just has density the viewport looks quite nice, but as soon as Cd is mapped it looks like the whole volume das density values greater than zero.
Is it possible to check color ( Cd ) values with the slice tool ? For me it just worked on density.

martin

I tried like hinted in this thread :
http://www.sidefx.com/index.php?option=com_forum&Itemid=172&page=viewtopic&p=87378&sid=a4f408313b2cd666af764ef876fed630 [sidefx.com]
to crank up to colors to ranges of 0 to 100 ( from 0 to 1 ) and enabled pbr rendering but I dont get any glowing, emitting volumes.
Can someone give me a hint what I am missing ?
thx martin

This isn't that straighforward. Firstly the default smoke (volume) shaders deal with reflected not emitted light. For your rainbow to emit light you need to use something like the flames shader, which allows you to emit light from a volume. I've converted it to do this in the attached file. You need to convert all the fields to say density rather than temperature etc. and you need to set the color ramp to white, and then enable tint with point colour.

Secondly you need to use PBR rendering and on the shading tab make sure the diffuse limit is 1 or more. To increase quality increase max ray samples on the sampling tab, and if necessary decrease the noise level.

Thanks a lot. It really starts to look great. Maybe you can answere one more question.
I think I understand the diffuse limit parameter, but what is the volume limit parameter doing ? Shouldnt this be the parameter to set above 1 ?

I wanted to share a working version of this rainbow scene ( thanks to peter ) ..

nice