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Can I 3D track an object?

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Pro Effects MAX

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Can I 3D track an object?

PostWed May 31, 2023 10:37 pm

I want to (instead of the normal 3D camera track), track an objects movement in 3d space. Is this possible?
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RCModelReviews

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Re: Can I 3D track an object?

PostThu Jun 01, 2023 12:42 am

How will you get the Z dimension from two two-dimensional footage?

Camera tracking is easier due to the paralax effect but it'd be a whole lot harder to track an object with only (perhaps) relative size to determine the Z dimension.
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Hendrik Proosa

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Re: Can I 3D track an object?

PostThu Jun 01, 2023 5:45 am

RCModelReviews wrote:How will you get the Z dimension from two two-dimensional footage?

The same way you get it for camera. Technically there is no difference between cam and object track, it is only a question of reference coordinate system. Either cam moves and object/world is stationary or object moves and cam is stationary. One is the inverse transformation of the other. In practice you would still get moving camera when doing it with cam tracker, so that object is stationary and cam moves. It should be possible to invert the movement and apply the transformation to an object too, needs some matrices juggling.

All constraints still apply, you need enough parallax in (object) motion, object should be relatively big in frame (otherwise errors are magnified) etc. Imagine it as a camera track done on limited scene, where only the part covered with object is what you can track from the entire environment. Helps wrap head around why it is harder to do.

Depending on what you want to do, cam tracking object might be enough. For projections etc it makes little difference what exactly is moving. When you want to render stuff with lighting etc, then moving vs static makes a visual difference as locations of lights (when stationary) either move in relation to object or they don't. If entire world is parented to camera then again it makes no difference.

Compound of cam and object track is where both move but these are solved by solving the cam first (from static environment), then solving object using camera path as constraint. Not sure how this should be approached in Fusion.
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JP Docherty

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Re: Can I 3D track an object?

PostThu Jun 01, 2023 12:35 pm

Don't know how easy it is in the fusion 3D camera tracker but Syntheyes has a full set of tools and tutorials for tracking an object. The simplest way is to mask out the object and track for a camera solve, then track the object and combine. But there are lots of permutations. If you google search
"syntheyes object tracking" and select "videos" you'll get loads of examples and tutorials.

It isn't free (https://www.ssontech.com/pricing.html) but I think it's still a bargain. The fusion export system allows you to take your solves into fusion easily too.
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bentheanimator

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Re: Can I 3D track an object?

PostThu Jun 01, 2023 5:01 pm

Watch this tutorial. It's about the best you can do in Fusion. SynthEyes is what I would go for if you plan to do a lot of it but this tutorial has given me a lot of room to do things like rotomation of a phone replacement in somebodies hand. A lot of times, if the movement is fairly limited in 2 dimensions, you can 2D track the object and then use that for the 3D render while only rotating the object slightly in 3D to match the dimensionality you need.

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Re: Can I 3D track an object?

PostFri Jun 02, 2023 2:27 pm

Thanks for all of the input, I was able to do it in my scene by simply 3D camera tracking my object, and the camera just rotated around my object basically replicating what an object track would do.
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Kel Philm

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Re: Can I 3D track an object?

PostFri Jun 02, 2023 11:00 pm

Hendrik nailed it, basically Object/Camera(Background) tracking is just about the point of refence so whatever you mask is what it will track, it doesn't know the difference.

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