[PD] motion-tracking

[B. Bogart]

Hi Sara,

I have a gem motion tracking patch I show students at:

http://www.ekran.org/pd/patches/Gem-Tracking-Presence.pd

As you can see I learned a lesson from then that relates to your questions:

1. X/Y coords from pix_blob are 0-1 not in gem units. (in the example
above I did some silly things to autoscale the units it gets to gem
units, but I'm pretty sure the scale is 0-1.
2. I have been unable to get pix_multiblob to work myself yet...
3. I've never used [showblob] abstraction??
4. Ok, I'll quote an email I already sent to the list:

> Gem coords really only represent distances relative to the window aspect
> ratio.
>
> 0,0,0 is in the middle, -4,-4,0 is the bottom left corner 4,4,0 is the
> upper right corner. The camera is at 0,0,4...
>
> That is for a square window.
>
> The height of a gemwindow is always 8 units, -4 to 4, but depending on
> the aspect ratio of the window the number of units wide changes. for a
> 2:1 window the left edge is -8 and the right 8. For a 4:3 window the
> left is -5.333 and the right 5.333

Hope that helps a bit.

.b.

sara kolster wrote:
> Hi,
>
> I'm trying to understand the Gem motiontracking objects, but I don't
> seem to get very far. The help patch of pix_movement shows the
> difference between two subsequent frames, but when I connect pix_blob
> (set to the alpha-channel) after [alpha] in the rendering chain, I have
> no clue what the relation is to the xy-coordinates that come out and the
> movement I see in my frame. When connecting pix_multiblob after
> pix_movement, the xy of'showblob' seem not to have any relation with the
> movement I see.
>
> Some questions:
> - what are the x/y coordinates in relation to my Gem window (defined in
> pixels) and the x/y coordinates of the objects [translateXYZ] or
> [pix_showblob]?  Or are the x/y coordinates related to the geo (defined
> in units) on which I texture my image?
> - Does [showblob] represent the movement? Let's say that if we have a
> red background and a green moving ball, showblob is following this green
> ball? Or is my understanding completely wrong/backwards?
> - Can anyone explain the definition of units, when p.e. rendering a
> rectangle of 3/4 in a gemwin of 800/600? I understand that 'units' are
> logical sizes in a 3d-application (from: Gem manual), but is there
> anyone who found a way to explain this better?
>
> Did someone succeed in making a simple motiontracking-patch, just so I
> can understand how these objects work?
>
> Thanks a lot,
> Sara
>
>
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