INS Assisted Monocular Visual Odometry for Aerial Vehicles

The requirement to operate aircrafts in GPS denied environments can be met by use of visual odometry. We study the case that the height of the aircraft above the ground can be measured by an altimeter. Even with a high quality INS that the orientation drift is neglectable, random noise exists in the INS orientation. The noise can lead to the error of position estimate, which accumulates over time. Here, we solve the visual odometry problem by tightly coupling the INS and camera. During state estimation, we virtually rotate the camera by reprojecting features with their depth direction perpendicular to the ground. This allows us to partially eliminate the error accumulation in state estimation, resulting in a slow position drift. The method is tested with data collected on a full-scale helicopter for approximately 16km of travel. The estimation error is less than 1% of the flying distance.