Systems and methods of tracking a mobile subject based on Global Navigation Satellite Systems (GNSS) data, including a boundary test unit to evaluate a boundary violation according to the current actionable position and current actionable speed of the mobile subject relative to a predetermined boundary, wherein the current actionable position is a sum of a prior actionable position and a product of a degraded position difference and a position tracking coefficient, and a current actionable speed is a function of a prior actionable speed and a degraded speed estimate.