Airborne GPS
HJW’s aircraft is equipped with an airborne GPS/IMU system that records the position and orientation of the camera platform during the flight mission. This system is linked to the camera’s shutter in such a way that a precise GPS time is recorded for each exposure. After the flight mission, in-house post processing establishes accurate position and orientation for each photo exposure.

Airborne IMU
Our comprehensive Applanix positioning and orientation system incorporates not only GPS, but also an IMU (Inertial Measurement Unit) sensor. IMU sensors are used to establish the three orientation angles of the camera platform. These three angles describe the rotation of the camera station with respect to the ground coordinate system. In aeronautics, pilots traditionally refer to these angles as pitch, yaw and heading. We are one of the few aerial mapping companies that operate and utilize an IMU in all of our flight missions.

IMU data is extremely useful for aerial mapping projects that involve rugged terrain or large water bodies, where ground control is not an option. Airborne GPS data alone is not adequate for high accuracy direct orientation (lack of ground control) because there is not enough information to constrain the aerial triangulation process. IMU data fills this gap and strengthens the geometry of the aerial triangulation for these areas where ground control is not available. In fact, aerial triangulation may not be necessary if using GPS/IMU.

With GPS/IMU-controlled aerial triangulation, HJW always incorporates redundant ground control to identify blunders, datum shifts, accommodate unforeseen system problems, and to find any systematic errors. Since HJW is a leader in high precision mapping, we make careful judgment as to the applicability of our positioning technologies to each project.