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3d motion tracking in AE

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Evan Robinson3d motion tracking in AE
by on Jul 6, 2012 at 3:33:39 pm

Hi all,

I have this green screen shot, where the camera is moving parallel to the scene. For some reason, AE's 3d motion tracker is having such a hard time tracking this shot. I finally got a solve error of under 2, at about 1.2. So i added a null object at the far left, as scene in the picture.
After i scrub through the video, since the camera moved about 15 feet to the right, the null object should be far to the left, but instead, once that point goes off the screen, it follows the green screen, and does not stay where it should.
If i add a null object to the green screen however, it stays in perfect position.
Any one have any ideas on what the problem is?


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Roland R. KahlenbergRe: 3d motion tracking in AE
by on Jul 6, 2012 at 4:22:44 pm

Insert both the point cloud *screen cap) and the original video. Otherwise I know of no way to see what the issue is.

Cheers
RoRK

Intensive AE & Mocha Training in Singapore and Malaysia
Adobe ACE/ACI (version 7) & Imagineer Systems Inc Approved Mocha Trainer


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Evan RobinsonRe: 3d motion tracking in AE
by on Jul 6, 2012 at 4:45:21 pm

What is the point cloud?? My problem is the null object it not staying on the ground in the second picture, the null object is still close the the scene, where it should be far to left, if it had tracked properly. Once the point that the null object is resting on in the first picture leaves the scene, the track messes up, and move along with the green screen, as if it was tracked to it.


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Roland R. KahlenbergRe: 3d motion tracking in AE
by on Jul 6, 2012 at 5:05:46 pm

Hi Evan, I understand the issue you are facing. Like you, I'd like to know what's causing the issue. I am assuming that you are using AE's built-in 3D Camera Tracker. When the camera solved has completed, you will see lots of points - these are what's commonly referred to as a point cloud.

So, post a screen cap of the image and the original video. Additionally, did you select one or more of these point clouds when you created the Null?

Cheers
RoRK

Intensive AE & Mocha Training in Singapore and Malaysia
Adobe ACE/ACI (version 7) & Imagineer Systems Inc Approved Mocha Trainer


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Evan RobinsonRe: 3d motion tracking in AE
by on Jul 6, 2012 at 5:22:05 pm

Yes, i selected more than 1.


The problem occurs anywhere on the ground, not just the point shown. It tracks fine, when the null is on the green screen


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Spencer TweedRe: 3d motion tracking in AE
by on Jul 6, 2012 at 6:51:09 pm

Hey Evan,

I assume that the green screen is being moved by those people? 3D Camera Tracking is a very delicate process and it is really a shame that Adobe doesn't give you more control...

Anyway, what I suggest you do is mask out anything which is moving in the shot (ie the people, and the green screen). In order for the plug-in to figure out what is the camera motion, it needs to not be confused by things that aren't perfectly still in the physical world - usually it can figure this out for itself, but in your case seems like it can't quite do it...

In other words it is watching your green screen move and thinks, "Oh my god, the whole world is moving this way - so I must be moving in the opposite direction." and that is what is throwing off your track (that's my guess, anyway). So by removing the confusing element the solver can go "Oh, it's actually moving that way... I see."

- Spencer


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Chris ButtacoliRe: 3d motion tracking in AE
by on Jul 7, 2012 at 4:15:21 pm

Just because the Null appears to be on the ground, back behind the garage, it could actually be hovering closer to the camera than the guy in the red shirt. Hence the weird paralax. You need to make sure that null is attached to one of the points from the cloud that is way back in z-space, like the ones on the grass by the parked car.


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Brian ScottRe: 3d motion tracking in AE
by on Jul 9, 2012 at 1:10:01 pm

Looks to me like the biggest problem is that there is not enough depth to the shot to get a good solve. Your tracking marks - such as they are - are moving throughout the screen and your only depth disappears part- way through the shot. For 3D trackers you need 3D info. It appears that all you have is a guy walking in front of a green screen. Why would you need depth info when you can create your own in the comp with a camera?

Brian Scott
President
Image Design Productions, Inc.


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Roland R. KahlenbergRe: 3d motion tracking in AE
by on Jul 9, 2012 at 1:29:05 pm

Evan, if you posted the original video, there would be more 'solves' from us COWpokes.

FWIW, it looks like you've done a tripod pan. This will work on most shots but if you want to ensure a camera solve, you should ensure that parallax is captured by your camera moves.

In this instance, your camera would be placed closer to the car on the left of the opening shot and then track backwards ('creating' parallax) as it dolly's to the right. Ideally, the imagery with obvious parallax (when the camera tracks backwards) should remain in the shot throughout. This is a good example of shooting at a higher rez or at least framing your last image to account for a camera solve and cropping.

HTH
RoRK

Intensive AE & Mocha Training in Singapore and Malaysia
Adobe ACE/ACI (version 7) & Imagineer Systems Inc Approved Mocha Trainer


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William CartwrightRe: 3d motion tracking in AE
by on Aug 29, 2012 at 8:52:54 am

I'm having a technical problem with my program, I can't seem to get the "red bullseye" to appear, I can create a camera and a text layer and etc. (even though I haven't been able to visible see the text no matter how big I make it) but the layer appears with vector handles.

Am I missing a simple on/off setting to see the layer?


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