As with a growing number of athletes, competitive skiers are looking to GNSS technology to help evaluate and improve their performance. Positions logged during practice runs or races can be transformed into 3-D models of the exact trajectories skied to measure velocity, accelerations, and other performance variables. However, obstructions along a ski run, such as terrain and trees, can block satellite signals - suggesting a need to add low-cost inertial sensors to support continuous, accuracte and affordable positioning.