Ground dust opacity by velocity?

[KristianThuesen]

I am a new user to phoenix but i already love it!

In the carpet bombing tutorial there is already a fat layer of dust covering the ground. How would one go about making that dust render only when it moves? that way the dust wont cover the ground until the shockwaves themselves stir them up.

I am about to do a anchor simulation where it hits the soft sandy seabed and would like the water and ground to be detailed with rocks and everything, then having the force of the anchor hitting to stir up the dust. I have tried doing this with vray distance texture and it worked ok, but not great up close.

Any suggestions here?

[LarsSonparsson]

Have you tried using velocity channel to control smoke density?
You could then have a fully transparent smoke until it starts to move.

http://docs.chaosgroup.com/display/P213M/Smoke+density

[KristianThuesen]

are you thinking of the speed option?

I am trying different to play with the different settings but i am struggling to get it to work.

[LarsSonparsson]

Ah, you are right. There isn't velocity option for smoke density anymore.
I'm playing with some ideas for it at the moment. I'll tell you later how it went.

[squintnic]

i would also like to know how to approach this.

[Svetlin.Nikolov]

Hey guys,

The Velocity is the vector speed containing the direction, while 'Speed' is the scalar value that contains just the magnitude. Speed in the smoke density should do the job.

@squintnic, you should make sure you have Speed or Velocity exported from the Output panel (Velocity will take 3 times more space than Speed in the cache files), and then you could use the Speed channel for the Smoke Opacity and draw an increasing line from 0 to 1 (this should be the default as well), so the faster the speed, the more opacity you would have.

Cheers!

[KristianThuesen]

Thanks for the good answer Svetlin! I thought it was weird as whatever i did in the speed curve didn't do much. Lets try enabling it in the output then :P


Edit:

Okay, so i have tested this a bit now and it does seem to work, but i am not getting the detail amount as opposed to leaving it at simple smoke.

when i bring the curve to start at 0 or 0,1 to be able to get as much as i can of the slowest moving smoke as well it seems to reveal smoke that is not generated by anything. Is there always a atmosphere within the grid?

This is with simple smoke in the smoke density tab



And this is the best i could do with the speed curve. I am problably just missing something here, but as you can see i am not getting even half of the details as the simple smoke result and i have tried fiddling back and forth with the speed curve.

[Ivaylo Katev]

i think with pure velocity based opacity the smoke will look weird, better use it as mask for the real opacity, using the modulate option. unfortunately this is not as easy as it sounds, because the circular references that will arise.
you will need two simulators, one to the velocity map, and one for the rendering.

[stevesideas]

I was looking for this option as well with a helicopter touching down. I have to have smoke already in the scene whereas ideally I would like it created as it start to move more. Is there still no way to do this ?

[Svetlin.Nikolov]

There is a way - you could shade the smoke by velocity and if the detail is not enough, you could base the opacity on Speed and also modulate it by a texture, which can be a Phoenix GridTex connected to that same simulator. There will be no circular reference as we reworked the connector and it should be fine.

You could also approach this as a simulation solution instead of a rendering one - you could use the V-Ray distance tex in the ground dust source so that it would start creating dust when the helicopter closes in. Another tool that ight be useful to you as well are the Discharge Modifiers on the source that can be set to emit only when the emitter geometry is moving.

Something that would be very helpful in your case is on our TODO list - getting sources to emit depending on some conditions in the simulator - e.g. the source will emit smoke only in areas of the simulator where the velocity is high.

[stevesideas]

I wouldn't know where to begin on shading the smoke with velocity. How do I go about doing that ?

[stevesideas]

There is a way - you could shade the smoke by velocity and if the detail is not enough, you could base the opacity on Speed and also modulate it by a texture, which can be a Phoenix GridTex connected to that same simulator. There will be no circular reference as we reworked the connector and it should be fine.

You could also approach this as a simulation solution instead of a rendering one - you could use the V-Ray distance tex in the ground dust source so that it would start creating dust when the helicopter closes in. Another tool that ight be useful to you as well are the Discharge Modifiers on the source that can be set to emit only when the emitter geometry is moving.

Something that would be very helpful in your case is on our TODO list - getting sources to emit depending on some conditions in the simulator - e.g. the source will emit smoke only in areas of the simulator where the velocity is high.

I've started another thread showing the pop-up issue with smoke but I think the opacity by speed option will probably resolve this. Not sure if you want to check the other thread out ?

Here's the link: http://forums.chaosgroup.com/showthr...op-on-creation