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Not enough Markers for a good track.

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Joe Cooper
Not enough Markers for a good track.
on Sep 29, 2011 at 7:06:31 pm

Hello Creative Cow Members,

I took some bad advice from my instructors at the time that i shot this footage, and
basically i didn't use enough markers for what I'm trying to do and am now having a hard time getting a decent track. I'm trying to combine the video with a matte painting then turn around and add some 3d elements in cinema 4d.

key2





If Anyone could offer a decent strategy to solve this problem i would be ecstatic, because i would rather not bother with a re-shoot; i don't think i can. I've tried mocha, AE, and The Foundry's camera tracker. Also, I have like a dozen more shots just like this one, although in some of them, the markers get obscured even more or less.

Thanks,

Joe C.


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ben g unguren
Re: Not enough Markers for a good track.
on Sep 29, 2011 at 8:28:53 pm

I can't get a good sense of your camera's type of movement from the shot you provided. If the camera isn't changing its position (only panning and tilting, essentially), then you only need one or two solidly tracked points to get the job done. Note that this is sometimes possible with handheld shots, if the camera remains in the same physical location, more or less (there may be some drifting when trying to "solve" a handheld shot as a camera-on-a-tripod shot, but with some shots it's the only possible solution).

If your camera is moving through physical space, then you're probably going to have to reshoot. For one thing, your tracker points are all on the same plane -- you need depth (foreground objects, background objects) in order to get a good 3D solution. And your trackers need to be spread out on the back wall. (You probably already know all this, but it's worth pointing out for other people who might stumble across this post.) The only possible thing that could save this is the rigging and other trackable data at the top and sides of the greenscreen (we only see it briefly in the shot you provide). If you have footage that includes those elements you might be able to grip onto something. But frankly, in my opinion, things look bleak if your camera wasn't on a tripod.

Ben Unguren
Motion Graphics & Editing
http://www.mostlydocumentary.com


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Joe Cooper
Re: Not enough Markers for a good track.
on Sep 29, 2011 at 11:29:53 pm

Hi Ben,

to quote you "you need depth (foreground objects, background objects) in order to get a good 3D solution. And your trackers need to be spread out on the back wall. (You probably already know all this, but it's worth pointing out for other people who might stumble across this post.)"

That's exactly the problem i realized, i didn't have any depth to track so my trackers fail, which i knew they would. But as far as camera movement is concerned. in the longer shots, its dollying in-and-out as well as panning left-to-right. Which equates to a quite a bit a of parallax.

but i agree with u that I might be out of luck.


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Roland R. Kahlenberg
Re: Not enough Markers for a good track.
on Sep 30, 2011 at 12:13:25 am

[Joe Cooper] "That's exactly the problem i realized, i didn't have any depth to track so my trackers fail"

Ideally, you should set up your markers with at least 3 levels of separation in z-space to give the tracker sufficient parallax. As Ben has mentioned, there could have been more markers placed along the edges of the green plate.

Your dolly shots will suffer a similar fate cos your trackers are meant to provide information pertaining to parallax. A camera dolly isn't going to help, given the placement of the markers that you now have.

Lastly, instead of conventional markers, look into using cutouts from magazines, specifically advertisements. These usually contain white spaces and other imagery that together provide lots of high contrast areas and hence, are more relevant to a tracking engine than a plus/target image.

HTH
RoRK

Intensive AE & Mocha Training in Asia.


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Roland R. Kahlenberg
Re: Not enough Markers for a good track.
on Sep 29, 2011 at 11:48:41 pm

For a 3D track, you're essentially screwed.

I am however surprised that you haven't been able to track the markers with Mocha or AE.

Here's a trick that should be handy but you will need to track the markers with either Mocha or AE.

With AE, perform a Stabilization routine. Then convert the footage to a 3D layer. Then create a camera and make the camera a child of the stabilized layer. From here onwards, any 3D layer that you place into the comp will incorporate the camera movement. This will come in handy when you roundtrip to C4D with AE's camera. Of course it'll also work well for your matte painting.

HTH
RoRK

Intensive AE & Mocha Training in Asia.


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Joe Cooper
Re: Not enough Markers for a good track.
on Sep 30, 2011 at 12:01:16 am

I did track them ok with mocha and Ae, But in some of the shots (like 5)
there would be some frames where all of the markers are blocked. I tried fixing those frames by hand and averaging a bunch of tracks. But if there's something else i could try, i'm all ears. eyes?


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Roland R. Kahlenberg
Re: Not enough Markers for a good track.
on Sep 30, 2011 at 12:14:47 am

It's only a few frames so you should be able to eye-ball a decent result.

HTH
RoRK

Intensive AE & Mocha Training in Asia.


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