One measure survives perspective, one does not
The crossing point does. Straight lines stay straight under perspective, so where two drawn lines cross in the image is where they cross on the ice. Simulated against a goalie-cam view it lands within a point or two of the truth whenever the crossing falls inside the stance.
Squareness does not. An angle in a photograph is not an angle on the ice. In the same simulation a stance that is exactly square reads about 23° off square, and the turn comes out the wrong way round a quarter of the time.
Marking the ice fixes it, and nothing else does. A reference line drawn at the shooter was tried and removed: recovering a short line’s direction from 25–30 ft out, on a camera only a few feet above the ice, costs more than it gives — 13° on average and 29° at the ninetieth percentile, against 3° for the same line drawn at the goalie. Square to the puck needs only the puck’s position, which survives that distance far better, so that is what the number is.
Two different faults
Centring asks whether the puck line splits his stance. Squareness asks whether his chest is turned to the puck — the angle between the puck line and the stance line, where 90° is facing it.
They fail independently, and the correction differs. A goalie can be perfectly centred and still turned, and retreating from there runs across the angle instead of down it.
When he is already down
The reference is the back of each blade — the heel line. That is also where the ABCD depth bands are defined, so the depth reading and the band agree without a correction.
If he is in butterfly or mid-slide at release — often the case on the goals worth studying — mark the back edge of each pad instead, which keeps the same reference. The geometry is identical; only the landmark changes.
Keep it consistent within a game or the numbers will not compare.
Mark whatever paint you can see
The camera is set by seven clicks in a fixed order: the two posts, the crease, and the blue line where it meets each set of boards. The board ends are known points on the ice — 64 ft out and 42½ ft either side of centre on an 85 ft sheet — so they pin how wide the zone is as well as how deep, which is what the blue-line and dot angles depend on. The faceoff dots are an optional extra; add them if the dot lines miss the real dots.
Published accuracy figures are worthless here, including the ones this page used to quote: they depend on how far back and how high the camera sat, which changes by rink and by period. So every number carries a ± measured on your own frame — the marks are resampled a pixel or two either way, two dozen times, and the spread of the answers is the figure shown. If the ± is wide, that frame cannot support that measurement, whatever a table says.
Mark the puck where it meets the ice. Everything clicked is assumed to be lying on the ice, so a puck a foot in the air reads about two feet further out. On a tip or a raised shot, treat the zone as a floor.
Set the sheet width with the rink selector: 85 ft for NHL and USA Hockey rinks, 98 ft for Olympic. A wrong width tilts the blue-line angles.
Before the camera is set you still get coverage — the shadow his stance casts on the goal line, seen from the puck, with the daylight split glove side and blocker side. It is the skate line only, so it is not how much net he really covers, and it moves with angle as well as depth: a deep goalie and a badly shaded one both lose coverage. Depth in feet is the clean number; coverage is what that depth bought him on this shot.
Working with video
Load any video file from your computer; nothing is uploaded. Space plays and pauses, ← → step one frame, Shift steps ten. L plays and each press doubles the speed (1×, 2×, 4×, 8×); J does the same backwards; K stops. Clicking the picture while it plays pauses it.
The posts, crease and blue line are the camera’s references, set once per clip and remembered for that file. Leave the blue dashed paint on while it plays: if it slides off the real lines, the camera moved — pause there and press Camera moved, which starts a new set from that moment, copied from the last so you only drag the marks back onto the paint.
Frame numbers come from the fps setting; the page measures the rate while playing and sets it for you. 4K HEVC from a phone or action camera plays in Safari; if Chrome shows a blank frame, convert to H.264 or use Safari.
Working quickly
After the references are set, each play is three clicks: left skate, right skate, puck. Log keeps the posts and clears the rest.
Drag any placed point to nudge it. Undo point steps back one. A loupe follows the cursor so you can place on the puck rather than near it.
To save a marked-up frame, right-click the canvas and save the image.