[PD] using 2 web cams with GEM for multiblob

IOhannes m zmölnig zmoelnig at iem.at
Sun May 17 21:23:53 CEST 2009


punchik punchik wrote:
> Hello, im working on a interactive installation, im using a web cam in the roof to track the movements of people in a space. The thing is that the roof is not so tall, so i just can track a little space. So i was wondering if a i oould use 2 web cams in gem and render both videos as textures in one square in gem. I need to join both videos from the web cams into one for using the pix_multiblob object to tracking multiple blobs.
> 
> Is this possible? Do anybody have tried this before?
> 

hi

first of all: i have used Gem with multiple cameras, there is no real 
problem doing so.

then: no you cannot texture 2 pixes onto a single square as you would 
like to

then: [pix_multiblob] has no notion of what a pix is textured to, so 
managing to put 2 pixes on a single geo will not help you with 
[pix_multiblob] at all.
instead, [pix_multiblob] will always work on a single pix, so what you 
really have to do is merging the 2 pixes into 1.

there are probably a number of ways to do so; the one that comes to my 
mind now is rendering to a framebuffer (with 2 geos) and grabbing the 
pix-data with [pix_snap]. this feels ugly (performance wise).


however, you could use 2 [pix_multiblob]s (one for each cam) and merge 
the meta-data.
this is probably easier. you will get some problems if a blob wanders 
from the view of cam1 to thhat of cam2.
try to setup the cameras with a sufficiently overlapping area (or no 
overlapping area at all), so that you never have a blob being partly in 
cam1 and the other part in cam2 (which will result in 2 small 
disconnected blobs), but either in one of the 2 cams or in both of them 
(or none of them -))

i imagine the problems be easier to handle then to try to merge the 2 
images smoothly.

mfg.asdrt.
IOhannes







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