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Greenscreen with 3D Camera Tracker tips?

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Matthew Beall
Greenscreen with 3D Camera Tracker tips?
on Aug 21, 2016 at 2:28:32 am

I will be shooting a greenscreen scene next week. I can bring avery stickers for tracking.
The camera will be on a jib and the director wants to do lots of camera moves.
I do not think any shots will be full body and show the floor, so there will probably only be one trackable plane.
Any tips to make sure I get a good camera match for a virtual room in AE?


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Spencer Tweed
Re: Greenscreen with 3D Camera Tracker tips?
on Aug 21, 2016 at 4:02:38 am

Your life will be hell if you do not go out and get a bunch of little stands to place all over the place. Trust me... If you only have 1 plane to track your solve will either fail or suck, no matter what software you use (I've professionally used AE's tracker, syntheyes, boujou, 3D Equalizer, PF Matchit and Nuke's cameratracker...). Granted I'm not the world's expert on matchmoving but I've done my fair share, and I've supe'd on set plenty of times.

What I've done in the past for a shot like this is get a few of these guys from one of the gaffers (or grip or whomever is your friend): https://static.bhphoto.com/images/images500x500/Matthews_B756040_Hollywood_....
Extend the arm out at whatever angle you want and tape 2-3 of these suckers on there: https://www.flickr.com/photos/alba/2505310839/.
Now just make sure of 2 things: A) you have the c-stands at different depths from the camera (a few feet, a few yards, etc depending on the size of your set), B) they don't go behind your actor unless you like roto.

- Spencer

PS I actually like another type of stand that is much smaller and light-weight but I forget what they're called. They look like a thinner c-stand and are usually black instead of the traditional silver. I think the stills guys use them for umbrellas and flashes and the like.


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Matthew Beall
Re: Greenscreen with 3D Camera Tracker tips?
on Aug 21, 2016 at 4:08:07 am

Spencer,

Thank you for the info! That all makes perfect sense.
I will have control over the shoot, so I can put as many c-stands with trackers on them I need.
We shoot wed, but the set will be ready Tue and I can run a test.



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Matthew Beall
Re: Greenscreen with 3D Camera Tracker tips?
on Aug 21, 2016 at 5:22:09 pm

Spencer,

Is there any need to take notes on lens info, distance between trackers, etc..?



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Matthew Beall
Re: Greenscreen with 3D Camera Tracker tips?
on Aug 22, 2016 at 11:09:44 pm

I printed out the tracking markers for $28 at Walmart on a 20x30 board print. It is very thick cardstock, almost like plastic, but I was able to cut it with heavy scissors. They should last a long time, and much better than printing paper and gluing them to cardstock/foamboard.
10463_vfxtrackingmrkr20x30.pdf.zip



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Spencer Tweed
Re: Greenscreen with 3D Camera Tracker tips?
on Sep 1, 2016 at 12:36:01 am

Nice! Last time I did this I just glue-stick'd a printout of the marker onto a piece of cardboard. Your method seems much more professional ;) Just make sure your paper is not reflective or you'll have problems. Trackers typically hate luminescence changes, so the more matte the better.

- Spencer


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Spencer Tweed
Re: Greenscreen with 3D Camera Tracker tips?
on Sep 1, 2016 at 12:44:52 am

Lens info absolutely. But truthfully it all depends how far you're planning on taking this shot. If you want to go all out you would do the following:

1) focal length of that shot. Avoid zooms but if a must, at least get the starting and ending focal length.
2) film back size. Or at least note exactly what camera you're using so you can look it up later.
3) lens grid for undistorting your footage. This goes beyond the scope of After Effects but if you're going into PFMatchit, Syntheyes or anything heavy-lifting like that it can seriously improve your track. If you think about it most lenses distort at least a few pixels (if you're lucky). Well imagine all of your tracks drifting a few pixels! It can make a difference. And trying to undistort footage without a lens grid is, in my humble experience, often worse than just leaving it (particularly on greenscreen where you have very little data to work with).
4) distance from camera lens's nodal point to a key object.
5) height from ground to camera lens's nodal point.
6) survey data - such as object sizes and distances.

The last two are only really needed if you are going to be re-creating your set in 3D and trying to match 3D objects in. it doesn't actually improve your track very much unless you're going ILM style with LIDAR scans and stuff. Which I seriously doubt... but would be pretty damn fun to play around with. Anyway the AE cameratracker doesn't have any use for real-world survey data unfortunately, so you can probably skip it.

Good luck!

- Spencer


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