[PD] motion-tracking

[sara kolster]

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