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Thread: shooting sparks

  1. #1
    Registered User Jakkar's Avatar
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    shooting sparks

    I have a job that requires sparks shooting our from train wheels as it slams on its brakes. This is not the first time. I was given this grinding wheel photo as reference.
    Has anyone been able to duplicate this look?
    Try as I might, I can't get particles to take on this appearance. Even with photoreal motion blur, stuff traveling this fast has very angular and faded blur instead of these bright, curving paths. I think it has to be done with a cheat.
    Appreciate any help...
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    Last edited by Jakkar; 06-24-2008 at 12:28 AM.

  2. #2
    Dimension the Third voriax's Avatar
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    Tough one.. You can get so close using particleFX but you can't do the curving paths with particle blur.
    I'm getting (sorta) close by using highly luminous objects linked to a particle emitter, with high PR blur and multiple blur passes. That will allow you to get the curved motion.

    Maybe it's just not possible in LW though...
    Last edited by voriax; 06-24-2008 at 02:03 AM.

  3. #3
    Goes bump in the night RebelHill's Avatar
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    Photoreal MB should deal with things using HDR values... u can either use objects attatched to particles, or the particles themselves I would have thought... and turn their brightness/luminous way WAY up over 100%, and prmb ahould create this streaking for u.

  4. #4
    Pixel and Poly Pusher JeffrySG's Avatar
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    Just a though:

    Would there be a way to use some wind emitters to push different groups of sparks into slight arcs like that?

  5. #5
    I agree with JeffrySG.

    I think you can use several different wind emitters with varying degrees of strength.

    Also, the Proton Videos have a tutorial with water flowing through pipes using several "guides" to control the water flow.

    May be worth checking out to see if would work for you, too.

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  6. #6
    Registered User Jakkar's Avatar
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    Ok, the problem isn't how to vary the paths, that's pretty basic with particles and wind. Maybe I didn't explain it well. The problem lies in getting the motion blur to render the arcing path properly. Moving an object very quickly and rendering one frame with photoreal motion blur works well. But when you attach geometry to a particle system, the blur does not render curved paths well. Instead, each blur pass creates a hard looking angled blur vector, not a smooth curve as it should. This seems to be a problem with the particle system.
    I'll post images of what I'm getting...

  7. #7
    Registered User Jakkar's Avatar
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    blur tests

    Ok, here's an example of what I'm experiencing...
    The nice curve on the right is from 1 object traveling a curved path over 3 frames, this is a render from frame 2 with the real lens camera, AA set to 2 with 40 blur passes. Perfect, exactly how you'd expect real motion blur to work.
    However, as you can see on the left, I attached a clone of this object to an emitter using fxlinker. The emitter settings approximated the velocity of the single object over 3 frames. Added enough gravity and wind to see the attached ones traveling in an arced path. And if you scrub the timeline with "allow fractional frames" on, you can see the curvature as they travel. However, the motion paths of the particles in the GL view show up as straight line vectors that suddenly pop and change after a point. And this is what renders as well.
    Very frustrating. I know from other posts that this also occurs when using hypervoxels and "particle blur" selected in the camera settings. But this doesn't use the particle blur setting as these are actual objects, and still getting this.
    Anyone have success getting curved blur out of particles? Or is this simply impossible with LightWave?
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  8. #8
    Unregistered Guest Sarford's Avatar
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    Don't know if it is possible in LW, but what if you bake out the motion of the objects, get rid of the particles and then try with motion blur?
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  9. #9
    Recycled User vfxwizard's Avatar
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    Quote Originally Posted by Jakkar View Post
    Anyone have success getting curved blur out of particles? Or is this simply impossible with LightWave?
    It can be done, but I don't know if it fits your scene (as it requires a separate render pass).

    To the best of my knowledge LW's motion blur interpolates deformations linearly so you have to cross the border between frames to get more points and define a curved path.

    So set Blur Length to an high value, say 1500%, and a large number of passes. Particles will draw curved trails, very effective for wispy smoke. Hope it can work for sparks as well, but timing will be way off wrt to what you see in Layout.

    BTW, Sarford's idea is likely to solve your problem better than this trick.
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  10. #10
    Goes bump in the night RebelHill's Avatar
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    U can use the editfx tab after calculating ur pfx to bake down the paths the particles take to standard object motion paths, or curves... then it should work as per ur working example once the motion is "free" from the emitter.

  11. #11
    Registered User Jakkar's Avatar
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    Quote Originally Posted by RebelHill View Post
    U can use the editfx tab after calculating ur pfx to bake down the paths the particles take to standard object motion paths, or curves... then it should work as per ur working example once the motion is "free" from the emitter.
    Thought of that, but this has to be a huge shower of intermittent sparks with the flexibility to modify the intensity, speed, size of the bursts etc... Saving out hundreds of motion paths is not practical in that case.
    Lightwave needs a serious overhaul of its particle system. It has remained unchanged for too long and is definitely behind max and maya in this regard.

  12. #12
    Super Member LightFreeze's Avatar
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    could you increase your frame rate when you calculate the particles then play them back slower when you go back to your original frame rate or put a step value in when rendering to get back your fps
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  13. #13
    NewTek Developer jameswillmott's Avatar
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    Quote Originally Posted by Jakkar View Post
    I have a job that requires sparks shooting our from train wheels as it slams on its brakes. This is not the first time. I was given this grinding wheel photo as reference.
    Has anyone been able to duplicate this look?
    Try as I might, I can't get particles to take on this appearance. Even with photoreal motion blur, stuff traveling this fast has very angular and faded blur instead of these bright, curving paths. I think it has to be done with a cheat.
    Appreciate any help...
    Can you film the real thing ( use a grinder, not a train :P ) and fake it all using a textured polygon?
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  14. #14
    Registered User Jakkar's Avatar
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    Quote Originally Posted by jameswillmott View Post
    Can you film the real thing ( use a grinder, not a train :P ) and fake it all using a textured polygon?
    That's why we're trying it in 3D now. Originally (as would be the simplest solution) was to use grinding wheel stock footage (see my original post with reference from this) and track it in behind the wheels in a compositing package like Flame. Problem is, the director wants it to be more intermittent, bursty-er, which you can't really do to the footage. Sure you can scale it down and dim it out, but it looks scaled and dimmed. What you need is a birthrate, particle speed ramps, gotta go 3D particle system.
    Trying a cheat now...more soon.

  15. #15
    You might want to try by calculating pfx as always until you get the sparks motion you are looking for (render with 50-100% mblur). Later in post, you can exaggerate the mblur effect.

    A test with 100% LW mblur (particle mblur) and Eco filter from AE:



    Eco filter can slow down sensation of speed:



    so you may want to stretch the duration of the final comp for this particlefx pass, I guess.



    Gerardo

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