No prize My solution was disqualified from the 3rd prize, because it made predictions on the subset of videos, not all of them. I disagree with this decision from the org.
Leak Sample submission had a leak: it was constructed as:
SampleSubmission = GroundTruth + Delta
Just submitting sample_submission.csv file gave a high score 130089.426 and some participants have figured it out. It is possible that Delta was not random, may be even constant. So fitting this Delta would provide a pretty high LB score. I didn’t try it, but it is possible that some participants did.
Solution The core of my approach was to find the position, angle and focus( or zoom factor) of the camera in the physical space. I used the following projections:
(3d physical space) <-> (camera lens) <-> (2d rink plane)
(ImageCoords) <-> (camera lens)
The approach was to figure out angles between individual frames in the video and collate frames to build a panoramic view of the rink. Then I could project each image to the panoramic view on camera lens and then onto 2d rink space. However, I noticed that some videos had a fixed camera, that didn’t move, rotate or zoom, so I decided to drop all this complexity and final submission was pretty simple: just find that fixed camera coordinates and angle and use them to project. This only worked for 3 videos, but was enough for #3 place.