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Sney23

motion tracking an object in 3d

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hi there folks,

 

my first post, so apologies if I'm missing any kind of etiquette here.

 

I'm trying to work out th best tool to track a handheld 'wand' in 3d. The wand is partially wrapped in green tape (to make it contrasty for extraction/tracking).

 

The objective is to replace the green section of the wand with an alien probe type object that will be built in 3d. All the 3d trackers I'm looking at talk a lot about match moving the camera so that objects can be inserted into the shot, but I just want to track the motion of the character raising the wand into shot and out again.

 

Any ideas? I will try and attach a screenshot...

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You need to solve the camera AND the object, othewise how will you be able to place the object in context in the shot?

 

I assume that there is some perspective shift, parallax etc otherwise you could just track with Mocha or whatever. What you want to do is a common VFX problem, the help documents for SynthEyes or other popular tracking application will cover this process in full.

Dan

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cheers Dan, appreciate you pitching in here.

 

The main camera is fixed, but yes there is perspective as the wand is raised into frame but then basically only has some lateral movement as it's help up to be seen.

 

Aside to this, I have no idea how to post a video of it here, this site isn't particularly helpful in terms of explaining basic usage... e.g. I keep accidentally posting things twice, but have no clue how to remove the duplicate posts. Irritating.

 

here is a link to the shot on youtube

 

 

So you're saying I have to solve the object. Ok at least I'm learning the terminology I should be searching for. After looking at the shot, do you think Syntheyes is up to it? Ideally it would provide me 3d transform data as I'm building the CG element in a 3d app....

 

I was a little shocked to see this post has been viewed 308 times, though with only one response. I'm new to posting on these forums, so I'm not sure what to expect... :)

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Not to try to disuade a hammer from searching out a nail, but using all the camera solve / tracker / point cloud / craziness on this shot seems like head-scratching overkill and more work and complication than it really needs to be.

 

I would just massage some old fashioned manual key-framing.

 

Or some quality time spent with built-in AE tracker with some rotational/scale tweaking.

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@jon Ha yes, I see what you mean having viewed the shot. Since there's no camera movement in the shot you could just animate the wand in your 3D package of choice.

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Yeah I agree, at least in this shot there's no camera movement, so no need to bother with 3D solving. In fact, it will get confused because the plastic is in fact moving in the bg, but the camera isn't so you'll get some weird looking tracks if you use syntheyes. I would probably start with the AE tracker and attach my rotating-but-not-moving 3d object to that. You can also put a clip in C4D as a background, and click through it's frames moving your 3D manually. Obviously not ideal, but I've done it before and it works. There is also a method of pasting position keys from AE into a text document and importing them in the structure manager of C4D. Also another sort of archaic solution, but great for learning things.

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