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View Full Version : Heat Distortion in XSI?


RobertTMiller
02-20-2009, 04:49 AM
Hello XSIheads.

I've been working on a VFX shot for a short film. The shot is a quick flyby of a UH60 chopper heading towards Chicago.

Here's the scene:
http://www.vimeo.com/3256821

I've got it to a level where I'm pretty happy with it, just sort of tweaking it to get it where I want it.

However, I want to add some heat distortion coming from the chopper's exhaust. I feel this would be a knock out punch to the shot.

But I'm having trouble pulling it off. I assume heat distorition is going to be some sort of dynamics simulation, but google searches have brought up little help.

Based on the few returns I did get with google, I managed to sim this with legacy particles Fluid V2 (sorry, can't find the link for where I grabbed the add-on) simulations:
http://www.youtube.com/watch?v=9hbFXRxMnvc

That's OK... needs lots of work... the general idea is that you've got a clear sim that distorts images behind it.

Problem with using the FluidV2 is that when I animated it, when I move it along with the chopper, the effect is borked and looks terrible. I haven't figured out a good solution to this yet.

So,

how would you guys go about simulating heat distortion in XSI?

And on a related note... is there any way to attatch a particle emitter with an object, like the UH60 model?

-Bobby

Pinionist
02-20-2009, 10:59 AM
Of course, you should pick "Particles from Selection" option. Then really, any kind of particles should suffice, as you would use this extra pass of particles as a displacement/blur map for the image. Really simple particle system would suffice for this.

RobertTMiller
03-14-2009, 05:47 PM
*smacks head

Yeah, particles from selection. Makes perfect sense. Rather disturbed I didn't think about that earlier. (I'm still quite n00b with particles)

How exactly do you set a displacement/blur map to a particle cloud? When I used the Legacy FluidV2 shaders, it was already set. I know there's got to be an easy method for plugging in a shader, but I just can't seem to find it.

Like I said, I haven't worked much with particles.

Pinionist
03-14-2009, 07:33 PM
If you want to add turbulent motion to your particles, in simulation tab add Turbulence in Forces. Connect it to the particles via environment\add force (or sth like that).

Blur, well, that would be motion blur.

PureMoxi
03-26-2009, 11:15 PM
The displacement or blur could be accomplished through motion blur (As Pinionist stated) or it could be done in post with something like real smart motion blur in AE or Digital Fusion...you could render out a raster motion pass from XSI...just an additional thought in case you run into issues with the motion blur rendering out in a timely or predictable fashion.

However, I think another thing to consider is the particle shader. I think a lot of the effect of a heat distortion is the refraction paired with transparency to give it a wobble and wavering effect. Although this is a completely lame, you get the idea with the first bit from this ref:

http://www.youtube.com/watch?v=moX6Lps9w70

Personally, I think you might be more successful and slightly less aggravated by trying to emulate this effect in comp since it happens so fast...might want to explore those options as well...as I do not know what software you are comping in, I really can't offer more detailed thoughts on that.

In the meantime, here is a post that has additional ideas:

http://forums.cgsociety.org/showthread.php?t=148001
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If you are from Elkhart...I'm hoping you are from Indiana...my South Bend sensibilities would dig it. ha.

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