LaserTagging (Technology)

Technology

Test Results

Performance

Testing has shown that performance with cameras that have automatic exposure control (which can't be turned off) is spotty at best. Performance on a windows laptop with a mobility radeon 9000 and a 3Ghz P4 is more than acceptable, but the faster the better.

Exposure

Webcams control exposure by a setting parametrised by a shutter time (ie: 1/20 s ), the inverse of which is obviously the maximum possible framerate sent by the cam to the bus. Many cams allow this to be set as low as 1/1000, but obviously both the encoder on the cam and the usb bus cannot handle these sorts of loads. 48fps @ 320x240 have been measured using a logitech communicate deluxe on linux. This is more than sufficient for good laser tracking as the tracking soft will probably max out at ~ 40fps on a laptop.

Settings

• Exposure autocontrol HAS to be disabled. (in low light conditions the framerate drops to 4-5 fps)
• Colours have to be set to something natural (the laser tracker uses HSV triplets to detect the laser spot).
• Brightness must be reduced as far as possible (the relative brightness of the laser pointer more than makes up for this), otherwise the tags themselves mess with the laser tracking (even if they are red).
• The best results were observed when the tags were barely visible on the camera image.
• It takes about 10-15 minutes to get the software set up correctly. It was observed that the best approach is to reduce each tracking option to zero (not all at once) and then slowly increment it until tracking works. Repeat for each and then go over the list again just to be sure.

Avenues for Tuning

I retract my statements about the software being written badly, however, performance profiling was obviously not done. Tschew 16:36, 27 March 2009 (UTC)

Resources

• Sam's Laser FAQ
• Diode Pumped Solid-State Lasers
• Nd:YAG/Nd:Nd:Y₃Al₅O₁₂ Laser
• Laser diode
• LaserLine Filters
• NYC Resistor Wiki Page
• 

  

  Sodium-tube wavelengths (courtesy of lamptech.co.uk)

Software

• http://openframeworks.cc/lasertag/LaserTag2002XPVista.zip
• http://openframeworks.cc/lasertag/LaserTag2002TigerLeopard.zip

Source

• http://openframeworks.cc/lasertag/LaserTag2002Xcode.zip
• http://openframeworks.cc/lasertag/LaserTag2002-VSProject.zip

Software Setup

• http://metalab.at/wiki/Laserguided_Graffiti_System
• http://muonics.net/blog/index.php?postid=15
• http://muonics.net/blog/index.php?postid=26