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 Post subject: Finding z-position from 2d plate
PostPosted: Wed Aug 25, 2010 3:08 am 
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Joined: Tue Jun 08, 2010 2:57 pm
Posts: 98
I posted this on the Adobe forums a couple of weeks ago: http://forums.adobe.com/message/3021469#3021469

Basically I would like to mimic Nukes' "PointTo3D" node. What it does is that it can find the proper z-position of an object in your 2d plate. You basically select the 2d position of your object in three different times in the timeline. Then you plug in your match-moved camera (you must have a camera) and press go. It somehow calculates the position with the three points and the camera. Very handy when you don't have a point cloud to your camera, or if you have to find a position for an object where you don't have a null.

Would this be possible to calculate via expressions somehow?


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 Post subject: Re: Finding z-position from 2d plate
PostPosted: Mon Jan 17, 2011 3:10 pm 
Triangulation.

You'd need to project 3 vectors from the camera through the 3 points. That bit's easy.

Then you'd need to compare the vectors in pairs and find where they come closest to one another. Then take the average of the 3 positions, I guess. The bit I've never done is the two vectors closest point part...

But there's a web page here with details... http://2000clicks.com/MathHelp/Geometry ... nes3D.aspx

I'd have to say... complicated.

-Ben.


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