Map the density of the Standard Volume

[Anonymous]

Hi. I'm working on a scene that involves several types of laser beams. They are modeled as cones and I was hoping to render them with the Standard Volume shader, but when a beam gets more focused (smaller radius) it becomes less visible instead of more visible.

So is there a way to 2D map the density so a small radius will light up more than a large radius?

[madsd]

Not entirely sure I understand, but intuition says Float ramp on a single axis, like v or u and then pipe it up and scale it.

[Anonymous]

Thanks for replying so quick! This screenshot might help. The diagonal part of the laser focuses on a small point and that's where I want the beam to be the most bright.

[madsd]

Added 2020 file as well.

[Anonymous]

Thanks for the effort! Still when I render the ramp seems to be aligned to the screen rather than to the object when viewed at an angle. I can't open your file because my workplace is still using Max 2019 (Arnold 3.0.77.0). Also my Ramp Float node has an extra input slot ("type").screenshot-2.jpg

[madsd]

Attached 2019 file.

Now I see your cone looks very different than mine, so I am not sure my setup is working for your item, but the gradient translates, so just adjust it so it works in your case.

[Anonymous]

Have you tried viewing it at an angle? Because your file has the same result (horizontal cutoff instead of object-aligned). You'll see it better with interpolation set to constant.

screenshot-3.jpg conev2.zip

[lee_griggs]

Btw, you can also achieve this with a spotlight using a high Lens Radius and atmosphere volume enabled.

[madsd]

That is because float ramp is screenspace pr default, you can map fix it in several ways.

I set up a camera projection here as an example:

[Anonymous · Accepted solution]

@Mads Drøschler could you please teach me how to adjust the Ramp from screenspace to object space? I still can't seem to make it work and I want to avoid using lights.

[madsd]

Try use a camera projection node, put the ramp into input and send out the info to the volume material from the camera projection shader, remember to pick actual scene camera ( you have to click a button in the shader UI and then pick the camera in the viewport ) - and adjust its position so it covers the item, now you can make a float ramp on a specific axis on the item.
If you need to animate the beams with rotation or soemthing simular, remember to move the camera projection camera with it, interconnect them.

[Anonymous]

That works perfectly! Thank you very Mads 🙂

[Anonymous]

Mads, thanks for your insights here. I'm having a hard time getting the camera projection to work the way I want- just a simple gradient or ramp on a box, where the bottom has a density of 1 and the top has a density of 0 and a clean blend in between. I'm trying to make an atmosphere box that I could stick in a valley to simulate an atmosphere that's thick down below and thinner higher up. You mentioned being able to fix the mapping of the float ramp in several ways- can you list some other options? Thanks so much!