Rink coordinates

The raw feed gives coordinates in the building's frame, not the game's. Teams change ends between periods, so the same shot from the same spot lands at opposite signs depending on which period it came in. Anyone binning shots by distance without fixing this gets two mirrored clouds and a shot-quality model that learns nothing.

These are normalised before they are stored, so every event is expressed as if the shooting team were attacking the same end all night. From 2019-20 the feed states which side the home team defended and that is used directly; before that it is inferred from the sign of a team's own attempts, which agrees with the stated value on 4,429 of the 4,430 game-period-team combinations where both exist.

That normalisation is what makes distance, angle and zone comparable across periods, seasons and buildings, and it is the step that usually costs a week when people build this themselves.