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Attaching Realflow emitter to an actors hand

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Mickey Ndubuka
Attaching Realflow emitter to an actors hand
on Sep 3, 2012 at 12:11:03 pm

Hello, I have a VFX shot to do where water sprays out of someones hands. Im using real flow and Maya. Does anyone have any ideas on how I could achieve. So far, i'm thinking I need to track the actors hands somehow, then attach the emitter to it, but how do i do that. Any advice at all would be much appreciated.
Thanks.


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Ben van Hamelen
Re: Attaching Realflow emitter to an actors hand
on Sep 4, 2012 at 3:39:37 pm

Alright, I think I got a decent idea, though my experience with RealFlow is very limited.

I'm not sure if you're stuck with the shot already or if it still has to be shot and you can be there to supervise. Because if the latter is the case, let them shoot it with a tiny tracking marker on his hand. Get the shot into PFTrack or whatever tracking software you prefer and track the marker (and preferably some other objects on different depths so you get parallax, which greatly improves your 3D tracking results).

I'm not sure if you can import tracking data into RealFlow. If not: pull the results into Maya. Your tracking points will show as locators. Maybe you can replace them by tiny cubes and import that scene into RealFlow. Parent your emitter to the cube that represents the hand-marker and you should be good. I would do it something like that.

TL;DR: Everything depends on the trackability of the hand, really.

http://www.fireinthesole.com/


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Mickey Ndubuka
Re: Attaching Realflow emitter to an actors hand
on Sep 5, 2012 at 7:24:19 am

Hi Ben, thanks for responding. The shoot is this Friday. That actually was the workflow I planned to use. Ill run some tests tonight when I get back from todays shoot. I normally track with Autodesk Matchmover.

Speaking about parallax, I know I need to track at different depths, I was thinking maybe all the trackers needed to be on his hands. I actually ran a test, and that failed because I couldnt find a solid way to achieve all the markers on the hand at various depths. your post has given me insight, can I actually put trackers in other parts of the scene to help the track, or must they all be on the actors hand?

Thanks again


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Ben van Hamelen
Re: Attaching Realflow emitter to an actors hand
on Sep 5, 2012 at 12:25:00 pm

Oh no, they don't need to be on just the hand. I think that it'd even be extremely hard to achieve parallax on just a hand. I figured it'd be nice to have some 3D coordinates you can use in Maya/RealFlow, so you have a general idea of the scale of the scene.

I would put three small* markers on the actors hand. That way you can accurately track his movements in 2D space, like rotation and position. The other markers in the rest of the scene will help you place the hand in 3D space.

* Keep in mind that you might have to do some marker removal in post. The smaller the markers, the easier it is to clean up (though possibly harder to track). But maybe the RealFlow stuff can cover up the markers.

http://www.fireinthesole.com/


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Mickey Ndubuka
Re: Attaching Realflow emitter to an actors hand
on Sep 6, 2012 at 12:14:01 am

Hello Ben. Thanks for the advice. Extremely helpful. Ill definitely give that a shot. hope I have time to test before the shoot.
Similarly, there is another shot where someone throws a spear as his opponent side steps it.. Its also meant to be a CG spear. Im going to model the spear, but would you have any advise. the shoot is tomorrow, im going to be on set, I know i'll need markers like you stated earlier, I'll be able to paint them out. (done some tests). Can you give me some more tips that may be useful and make post easier. I'm relatively new to tracking. Im thinking I need to give the actor something like a place holder also with markers on to hold in hand and throw.
Thanks again.


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Ben van Hamelen
Re: Attaching Realflow emitter to an actors hand
on Sep 6, 2012 at 8:36:16 am

That's not an easy thing to do. Here's why: As the actor throws the spear/playholder, naturally the object moves fast, generating motion blur. Motion blur is one of a matchmovers greatest enemies. It can be done, but it's hard.

Either way, I would give the actor a plastic tube. Apply some bright, easy to track tape at the ends and possibly some more towards the middle. As always, some extra markers at different depths is preferred. You could either go for traditional matchmoving, but maybe you'll get better results with object-based tracking. I'm sure Autodesk Matchmover supports that. Try which works best.

Closing, I don't know how experienced you are in matchmoving, but for the love of god: glue yourself to the cameraman. Ask him at which focal lengths he shoots during which scenes, what type of camera he has, what kind of lens, sensor, etc. You'll be annoying, but you will NEED that information. And if you're interested, check out Tim Dobbert's book 'Matchmoving: The Invisible Art of Camera Tracking', a.k.a. the matchmoving bible. I'm not an avid reader, but this one was very easy to get through and VERY helpful.

Let me know how it works out.

http://www.fireinthesole.com/


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