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3D camera tracking problem: footage or tracking?

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Joost van Doremalen
3D camera tracking problem: footage or tracking?
on Aug 6, 2012 at 7:39:31 am

I am experimenting a bit with camera tracking and shot some random footage, which I uploaded here:






The shaking was intentional btw :)

I am using the camera tracker from the foundry, but I am unable to find a solid ground plane. The average RMS error seems to be around 2.0. I can get it a bit lower, to 1.7, by removing some bad tracks. After that, when I create a solid from some points that seem to lie on the ground (tried different sets of points), the solid is unstable during the shot. My goal is just to place a 3d object on the grass.

Can I do something about this within the camera tracker of is my footage unfit for this type of analysis?


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Darby Edelen
Re: 3D camera tracking problem: footage or tracking?
on Aug 6, 2012 at 9:22:35 pm

The clip looks okay. It looks very close to a nodal pan which changes the camera tracking because there is little to no parallax.

Without parallax the camera tracker may have a difficult time determining things like the camera's focal length accurately. Take a look at your camera's motion path in one of the Custom Views and see if it's moving significantly. Were you standing still when you shot this? Do the camera's keyframes make sense? Does the focal length assigned to the composition camera seem right?

If not then you might try re-tracking the scene with "Rotating Camera" selected for "Track Validation" in the Tracking section. When solving you should also choose "Rotation Only" in the Solve section.

Beyond that I'd recommend making sure that you're not getting track points in the sky by creating a matte and setting your Matte Source in CameraTracker before tracking. The sky is too uniform to track reliably and too distant to really help in the camera solve.

Also if you know the focal length you used and film back for your camera then manually entering them may help get a better solve.

Darby Edelen


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Joost van Doremalen
Re: 3D camera tracking problem: footage or tracking?
on Aug 6, 2012 at 10:00:08 pm

Thanks for your reply, appreciate that.
The camera solve seems to look fine. I was standing still, but the camera moved a bit (no tripod) and this is reflected in the camera track. I tried retracking using your tips and that doesn't seem to change the camera solve a lot.
The main problem I get is when I try to make a solid that lies on the ground. On the grass there are only a few good tracking points and when I select them and make a solid the orientation is way off (and it is shifting during the clip).

Are there any tools to rotate the solid in perspective?
And if this doesn't work, would using mocha be an option?


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Tom Daigon
Re: 3D camera tracking problem: footage or tracking?
on Aug 6, 2012 at 10:33:06 pm

The Foundys Camera Tracker and Syntheyes both have the ability for you to tell the software that its a nodal pan. I suggest you download a demo of Camera Ttracker to be sure it can do what you want.

Tom Daigon
PrP / After Effects Editor
http://www.hdshotsandcuts.com





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Joost van Doremalen
Re: 3D camera tracking problem: footage or tracking?
on Aug 6, 2012 at 11:31:23 pm

Thanks, Tom. I'm not sure how cameratrackers in general handle this kind of 'imperfect' nodal pan (because handheld), but if I constrain the tracking and solution to rotation only the RMS errors rises to 4.2 and I am still not able to define a solid ground plane.

I am starting to think that the grass contains too few high contrast points for the tracker...


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Darby Edelen
Re: 3D camera tracking problem: footage or tracking?
on Aug 6, 2012 at 11:37:24 pm

Well, if you're happy with the solve then the best advice I can give to try and help with orienting solids would be to try and get the best set up for your ground plane that you can manage.

Try using Set Origin on a track point on the ground with good Point Quality. Then select a pair of points that lie on the ground plane and use Set X or Set Z to try and orient the ground plane. This can be hit & miss but you should be able to get a decent ground plane if you use good quality points.

Once you have that set an orientation of 0° on all axes will align your solid with the ground plane null. You should either have a floor or a wall with that orientation. If it's a wall then you should be able to rotate it 90° on one of its axes to make it a floor.

Darby Edelen


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Darby Edelen
Re: 3D camera tracking problem: footage or tracking?
on Aug 6, 2012 at 11:39:29 pm

I'll also add that as I looked closer at your footage it looks like there may be some Rolling Shutter or Lens Distortion issues, which could definitely throw off a track. I think it's the former since I'm only seeing it in high motion areas.

Darby Edelen


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