refers to the use of GPS
satellite signals to correct or calibrate a solution from an Inertial Navigation System
(INS). Inertial navigation systems usually can only provide an accurate solution for a short period of time. The INS accelerometers will produce an unknown bias signal that appears as a genuine specific force. This is integrated to produce an error in position. Additionally, the INS software must use an estimate of the angular position of the accelerometers when conducting this integration. Typically, the angular position is tracked through an integration of the angular rate from the gyro sensors. These also produce unknown biases that affect the integration to get the position of the unit. The GPS gives an absolute drift-free position value that can be used to reset the INS solution or may be blended with it by use of a mathematical algorithm such as a Kalman Filter
. The angular orientation of the unit may be inferred from the series of position updates from the GPS. The change in the error in position relative to the GPS may be used to estimate the unknown angle error.
The benefits of using GPS with an INS are that the INS may be calibrated by the GPS signals and that the INS can provide position and angle updates between the 1 second GPS updates. For high dynamic vehicles such as missiles and aircraft, the 1 second delay is unacceptable for guidance and control; the INS fills in the gap. Additionally, GPS may lose its signal and the INS can continue to compute the position and angle during the period of lost GPS signal. The two systems are complementary and are often employed together.
- MTi-G An integrated GPS and Inertial Measurement Unit (IMU) with an Attitude and Heading Reference System (AHRS) processor.