[Bf-committers] Camera tracking UI

[Keir Mierle]

*+bf-vfx*

On Wed, Nov 9, 2011 at 4:40 AM, François T. <francoistarlier at gmail.com>wrote:

> yeah I kind of agree with all that. So far all those naming as been chosen
> based on a technical naming side (ie bundles means something to a computer
> vision developer, doesn't mean a thing to an artist)
>

What do you propose instead? There has to be some name, either "point" or
"track". The problem with "track" is that it's highly overloaded. Same with
marker. It's not an issue of computer vision, it's an issue of simply
deciding on names. It IS important to have a way to refer to each of the
different concepts so that there is no confusion.

The naming we've chosen for Blender at the moment is:

A marker - a 2D coordinate on a single image. Literally, a struct of (x, y,
image#, track#)
A track - A collection of markers, one per frame, that point to the same
physical location in the scene. In other words, a collection of {(x, y,
image#)}. There is a 1-to-many relationship between a track and markers.
A bundle - The reconstructed 3D point for a track. Called a "bundle"
because if you visualize a ray from the camera to each marker, they
(should) intersect at a single point for a good reconstruction. The word
"bundle" is used to distinguish a reconstructed point from any regular
point. There is a 1-to-1 correspondence between a track and a bundle.

Here's where the overloading gets confusing:

A track*er* - The algorithm that tracks a marker from frame A to frame A+1.
In libmv right now, this is KLT and SAD. Ok, there's a few KLT variants but
they're similar. This is pattern matching across frames. There needs to be
documentation about why you would use one over the other (SAD is faster but
less accurate, KLT is very accurate but sometimes slow)

A tracker - Also the name used for general matchmoving software, e.g.
syntheyes, boujou, etc. Confusing! But there you go.

Feature detector - An algorithm to identify "good features to track" in the
image, for automatic tracking. Again, the best algorithm depends on the
scene. I wish there was One True Feature Detector To Rule Them All but
there isn't.


> Same confusion with, markers, trackers, ....
> Same with algorithm FAST, SAD, ... all technical stuff that doesn't mean a
> thing if you havn't done any computer vision dev in your life
>

I don't think we can avoid having good documentation.


> But in another hand, matchmove is something you have to get interest in as
> well. it is a discipline and not just a camera to move around :p. There are
> terms you got to know as well. Reconstruction is a common one for instance.
>

The difficulty is that if everything is made automatic with no choices,
then the tool is less useful since in many situations the difference in
whether you can track a shot or not depends on which algorithm you pick.

Welcome to computer vision, where the pixels don't care what you want :)

So yeah on the overall, lots of cleaning stuff to do, and lets drop the
> geeky dev side. This is a tool for artist and not for devs as far as I'm
> concern
>

Do you have concrete proposals to do so?

Keir


>
>
>
> 2011/11/9 Daniel Salazar - 3Developer.com <zanqdo at gmail.com>
>
> > Hi, i see that camera tracker related UI is spread all over the place
> > with no clear definition. Camera tracking is a corner case use of
> > Blender, I'd suggest that UI elements belonging to it get clearer
> > names *and* get pulled together in boxes or their own panels
> >
> > ie: follow track constraint
> >
> > http://www.pasteall.org/pic/show.php?id=20349
> >
> > why would any regular user of know that this is camera tracking stuff,
> > or what is a Bundle?
> >
> > it's worst in the N Panel
> >
> > http://www.pasteall.org/pic/show.php?id=20350
> >
> > Shading, Textured solid.. reconstruction? reconstruction of what??
> > bundle, bundle, bundle and then the old quad view!
> >
> > Daniel Salazar
> > 3Developer.com
> > _______________________________________________
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>
>
>
> --
> ____________________
> François Tarlier
> www.francois-tarlier.com
> www.linkedin.com/in/francoistarlier
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