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As promised here's the technique we used to create the volume for last week's tutorial. It's a setup we find ourselves using quite frequently in commercial projects, especially when it comes to still renderings. Creating a velocity volume to drive your advection makes the behaviour and look of your volume extremely adaptable and art directable. Which comes in very handy when you're trying to meet a client's feedback :)

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Volumes 101 pt. 21: "Dissolving" Geometry

Comments

Acroyear

Thank you for the cool technique. Is there a quick way to animate this or to turn it into a simulation?

Jose Medina

Thank so much man. this are great!

Mark Pamatat

im going to keyframe the ramp to animate it that way.. but there is probably better ways to animate it

Luis B

Hello Mo. You should be quite busy by now, but I try to ask anyway: how would you generate velocity out of a more complex and defined density volume? Using noise is already clear and effective in many cases, but let's say I want to advect particles through a Volume generated by a CT Scan. An object with stuff inside, but no infos about tangents or something similar. How to generate some Velocity info out of those density values? I'd guess using VEX to search for the voxel with the closest grey value to the actual one? Don't know, may be a good follow up tutorial?... :)

entagma

Hi Luis, why not use the volume's gradient? This gives you vectors pointing in the direction of the steepest descent of your volume values. Can be calculated either by using the VDB Analysis SOP or the Volume Analysis SOP - depending on the type of your volume. Cheers, Mo

entagma

Hi Raghid, make sure you enter density in the volume visualisation node's density attribute field. That changed a few versions ago. Now you can/have to specify which field to visualize. Hope that solves it. Cheers, Mo