G4-C2
Group 4 - Critique 2:
Introduction
FoxTrax - The glowing puck Fox used during National Hockey League games from 1996-1998 to help American viewers – who, it was claimed, had trouble following the puck – enjoy the game better. It was a publicity disaster and made a mockery of the game, but it's still kind of cool that they managed to do it. It was developed by News Corp. and Vista Research.
Plot Summary
I went to a fight last night, and a hockey game broke out!
The Effect
Example Video (not very good quality)
Television viewers would see a bluish glow around the puck as it moved around the ice. Additionally, when a player passed the puck, it would be followed by a blue streak, and when the puck was shot, it would be followed by a red streak.
How We Think it Was Done
There are several possibilities:
- Use real-time tracking software to add the glow to the puck. Calculate the speed of the puck from frame to frame to determine whether to add a blue or red streak.
- Embed an emitter in the puck to broadcast its position in the rink. Use a model of the arena to figure out where the puck is and the glow appropriately
- Similarly, place an accelerometer in the puck to record its velocity.
How It Was Actually Done
The hockey puck is modified to contain IR LEDs that blink at 30 Hz. Over the hockey rink are 10 IR sensors (cameras) which only detect the blinking. This is used to synchronize the shutters of the actual tracking cameras, so they only record when they can actually see the puck blink. The reason for this is to get a high SNR because the puck is not the only IR light source. When the puck is blinking the strength of the IR is high, but it is not strong enough against the accumulated light of the other sources. With this trick they only see the strong pulse of the puck and not the accumulated strength of the other light sources.
The actual tracking IR cameras are also mounted fixed around the rink (in later versions on the actual broadcasting cameras) and are then able to track the puck.
To generate the actual video overlay, the broadcast video is overlayed with a bluish glow when the puck is moving with a speed of less then 50 mph and reddish if above. The broadcast cameras are augmented with encoders which give the system the exact view of the camera so that the glow can be placed on the puck (same as with the 1st&10 system). The system can also integrate know boundaries of the rink to have some kind of translucency effect where the puck is not directly visible.
Because the system uses so many cameras, they use a regular PC for each camera and only transmit symbolic information to the SGI workstation which does the final calculations and the overlay. They did this to hande the performance requirements and to limit the bandwith needed from the PC to the workstation.
Alternate Ways of Doing the Effect
- Give the puck a IR refelctive coating and put strong IR lights around the rink. Might be a problem with the SNR.
- Place high-res high-speed cameras obove the rink to trak the puck with regular vision techniques.
- Embed a radar repeater in the puck to send out "chirps" which would be detected by microwave radars used to triangulate the position of the puck. They actually tried this, but the rink gave off too much noise, so the SNR was too low.
How This Applies to Our Project
- We are attempting to track football players, just as FoxTrax tracked a hockey puck
- They were able to set up the puck and arena in such a way as to make the tracking easier, including adding hardware to the puck. We do not have that option.
- We can use the same compression method with the symbolic representation. Our low level algorithms produce symbolic blob information and hand this to the higher level tracking system. Which doesn't have to deal with pixels anymore.
References
1. Cavallaro, Rick. "The FoxTrax Hockey Puck Tracking System." IEEE Computer Graphics and Applications. 1997 (Vol. 17, No. 2).
2. "Super Puck & FoxTrax." Vista Technology Department
Link to this Page
- DVFX 2007 Groups last edited on 2 May 2007 at 12:51 am by coppola-win.cc.gatech.edu