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Comment by yock | Hacker News Reader

How are the statistics from which these visualizations are generated captured? Does the NBA have equipment on the court or in the arena to track players and the ball (something like how professional tennis is monitored)? Is it manual, with a person recording their own observations about player/ball placement? Post-game video analysis?

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Not the NBA, but some teams use a system called SportVU[0] that do auto player&ball tracking.

I used to work on the system, so I can answer (some) questions about it.

[0] http://www.sportvu.com/basketball.asp

How does it work?

Short version: Using a number(six) of dedicated video cameras around the venue and (a lot of) image processing.

There is a nice article in wired about it(include a picture of one of the cameras and the view from another) http://www.wired.com/playbook/2011/04/nba-data-revolution/al...

How is the system calibrated? Are the cameras at fixed angles or mounted to a base that measures their angles?

The angles are important, but also the position relatively to the court(which is different in every venue).

The calibration is done by matching(automatically or manually) known world points to pixels from the cameras. (This is a very common practice in image-processing systems)

Teams can install these cameras in their own arenas. Are they allowed to install it when their team plays in opposing arenas? Do they have to negotiate with various team owners for this?

Unfortunately - they can't. There is a continues effort(by the company own the tech, and by the teams that are currently using it) to make it a standart in the league. At least in the previous season there was a sharing agreement between the teams that use the system(all the teams get all the data).

The NBA manually records where the shots are taken, and if it is made or not by the stat person.

I knew a guy in college who got to do this for the Sixers one year. He got to sit relatively court-side and just had to keep an key on the game and write down everything. He used pen and pad, but I would imagine that capturing that data is a lot easier today.

I was looking at espn's feed of the game the other night and they seem to have a lot of details about the game as the game is being played. things like "player missed 13 foot jump shot" and a graphic of a ball bouncing off of the rim and where it was shot from. Id imagine that they have a system like court stenographers so that they can quickly record info and send it to their servers.

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