[Bf-vfx] Plane Tracking naming

[Sean Kennedy]

That sounds like a good idea. Are there industry standard terms to refer to the different types of corner-pinning modes? Such as blender's Affine/Perspective/LocRotScale modes? Also, does "corner pin" imply a single image patch track as it does in blender?
Those modes you mention are not corner pin modes, but rather tracking solvers/algorithms. (Keir or Sergey could answer what those are far better than me). Those modes deal only with individual trackers. They don't really have anything to do with the technique of corner pinning an image, they are simply track modes. They deal with how the tracker follows the pattern around the scene, not with how the track data is used in compositing or elsewhere.
And no, corner pin simply implies a rectangular image is being deformed to fit into a defined rectangular patch that has been tracked into live footage using multiple tracks.
The single track perspective stuff Blender is doing when you set a tracker to use Affine or Perspective is actually planar tracking as generally accepted by the vfx community. However, there is no way to actually apply that planar data as a corner pin on it's own. That planar tracking is happening ONLY for the purpose of locking the individual track to it's pattern better.
If we could put one tracker into the shot, set it to Perspective, track a plane, and then use the new corner pin tools on THAT plane, that would be planar tracking as the vfx industry understands it.
What blender does with individual trackers seems really really different than what mocha does with "planar tracking". That feature appears to be a meta-tracking feature which automatically manages many individual tracks within a planar surface. >From this video on the mocha planar tracking..
Yes, in Mocha, you don't place actual trackers, it recognizes the entire feature inside the mask you create. It works as you describe, ignoring sections that become obscured or move out of frame.
In the example in that video, they draw a big mask around the screen, track it, then set up a corner pin on it, which magically sticks to the "plane" it just tracked. You cannot do that in Blender currently. You would have to track each corner of the phone, then place your corner pin box on the plane defined by those tracks. That is corner pinning.
And actually, Blender is sort of in-progress with actually being able to do exactly what Mocha does. The Ceres library is already integrated, and planar recognition is being used to make individual point tracks more accurate (that's the Affine and Perspective modes). 
Scroll down to the "Planar Tracking" sectionhttp://wiki.blender.org/index.php/Dev:Ref/Release_Notes/2.64/Motion_Tracker
But planar tracking is NOT yet being used the way it is in Mocha, to define an actual plane which you can then use to attach images to. It's strictly being used for more accurate point tracks.
When those tools do eventually work, those are the tools that should be called "planar". Pinning a plane to multiple point tracks is simple good corner pinning.

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On Mon, Aug 12, 2013 at 1:02 PM, Sean Kennedy <mack_dadd2 at hotmail.com> wrote:








I'd like to propose that the name of the new plane tracking tool be changed to something like Corner Pin, along with the plane deform node becoming something like Corner Pin Deform node.


That sounds like a good idea. Are there industry standard terms to refer to the different types of corner-pinning modes? Such as blender's Affine/Perspective/LocRotScale modes? Also, does "corner pin" imply a single image patch track as it does in blender?

 
(A single track set to Affine or Perspective actually tracks a plane. If we could then position the corner pin outline on a plane based of that single track, I would support calling that plane/planar tracking.)


What blender does with individual trackers seems really really different than what mocha does with "planar tracking". That feature appears to be a meta-tracking feature which automatically manages many individual tracks within a planar surface. >From this video on the mocha planar tracking..


http://www.youtube.com/watch?v=IjGsDMH2b5U

It looks like Mocha does (at least) two things I believe the current Blender tracker does not do: 


(a) the mocha "planar tracking spline" is not a tracker itself, but a tracking region, within which mocha automatically establishes several separate tracking chunk-patches -- think of each one of these patches like a blender affine-tracker 


(b) mocha tracks each  chunk motion (transformation, affine, skew, perspective) as a holistic integration across all those patches -- knowing they are part of planar object motion.


Using these methods gives it some accuracy benefits over what Blender can do today... (1) it can solve and validate the motion of each chunk constrained to the planar-motion derived from all chunks on the plane. (2) if any one chunk becomes permanently or temporarily invalid (such as because part of the planar content is changing) it can more easily reject that chunk as not conforming to the plane, rather than causing tracking error and drifting the individual chunk-track because of a mis-match. 


The analogous operation in blender would be to manually set several Affine or Perspective trackers across the plane (one for each chunk mocha automatically establishes), and then establish some kind of tracking-constraint across that set of trackers saying they should lie in a plane (which blender can't do AFAIK).






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