[PD] motion-tracking

[sara kolster]

Hi Ben,

Thanks for your help. When I open the patch and turn rendering on, my 
terminal keeps spitting out the following message:

/*separator : state->numTexCoords 4 != m_state.numTexCoords 0

*/I get the cursor to follow an object, only when pointing the camera to 
a steady background and using a very reflective object which enters the 
scene. I know that motiontracking is a very 'sensitive' thing, so maybe 
that's just how I should handle it.

This autoscaling from the x/y coordinates of pix_blob to Gem units is 
interesting. I see you're using the '8 unit'-fact of the gemwindow. 
Adjusting the window with another aspect ratio, means that I've to 
adjust the [expr] in order to make it [autoscale] again.

Thanks a lot and maybe till nxt time in Vancouver,

Sara





B. Bogart wrote:
> 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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