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:
- 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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