Sprint Analysis & AI Features
Cloud-backed pathfinding, GPS snapping, and Ghost Runners.
Sprint orienteering is fundamentally different from forest orienteering. It occurs in highly constrained urban environments with impassable walls, fences, and complex multi-level structures.
To analyze Sprints accurately, Routster offloads heavy computation to a serverless Modal backend, running advanced pathfinding and geometry snapping algorithms.
Enabling Sprint Features
Theta* Shortest Pathfinding
In a Sprint, the shortest path is rarely a straight line. Routster automatically calculates the true shortest route between controls, avoiding impassable olive green, thick black walls, and uncrossable fences.
We use a customized Theta* (Theta-Star) algorithm. Unlike standard A* (which restricts movement to an 8-way grid), Theta* allows any-angle line-of-sight paths. This produces highly realistic, smooth, corner-hugging routes that mimic a real runner, rather than jagged stair-step lines.
The output of this algorithm (a series of pixel coordinates) is cached in our Supabase database so it loads instantly for all future runners on that course.
GPS Snapping
Urban environments cause massive GPS drift due to multipath errors (signals bouncing off tall buildings). A raw GPS track in a sprint might show you running straight through a building.
Routster's refine-gpx pipeline takes your raw GPS track and "snaps" it to the passable terrain. It uses a Hidden Markov Model (HMM) and the Viterbi algorithm to find the most probable sequence of valid, passable pixels that matches your noisy GPS timestamps. The result is a clean track that perfectly hugs the legal route choices.
The Ghost Runner
How do you know if you executed your route choice well, or if the other option was just shorter?
Because Routster calculates the exact Theta* shortest path, it can generate a Ghost Runner. The system looks at how much time you took to complete a leg (e.g., 60 seconds). It then takes the calculated shortest path, measures the total pixel distance, and creates a synthetic, evenly-spaced GPX track along that line, completing it in exactly 60 seconds.
In the Live Mode Player, the Ghost Runner appears as a translucent chip. You can watch yourself race against the theoretical optimal path. If the Ghost pulls ahead immediately and beats you to the control, your chosen route was longer. If you beat the Ghost, you chose the shorter route!