Introduction

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Introduction

Grewal, Mohinder S. / Weill, Lawrence R. / Andrews, Angus P.

The five basic forms of navigation are as follows: 1.

Pilotage, which essentially relies on recognizing landmarks to know where you are. It is older than human kind.

Dead reckoning, which relies on knowing where you started from, plus some form of heading information and some estimate of speed.

Celestial navigation, using time and the angles between local vertical and known celestial objects (e.g., sun, moon, or stars).

Radio navigation, which relies on radio‐frequency sources with known locations (including Global Positioning System satellites).

Inertial navigation, which relies on knowing your initial position, velocity, and attitude and thereafter measuring your attitude rates and accelerations. It is the only form of navigation that does not rely on external references.

These forms of navigation can be used in combination as well. The subject of this book is a combination of the fourth and fifth forms of navigation using Kalman filtering.

Kalman filtering exploits a powerful synergism between the Global Positioning System (GPS) and an inertial navigation system (INS). This synergism is possible, in part, because the INS and GPS have very complementary error characteristics. Short‐term position errors from the INS are relatively small, but they degrade without bound over time. GPS position errors, on the other hand, are not as good over the short term, but they do not degrade with time. The Kalman filter is able to take advantage of these characteristics to provide a common, integrated navigation implementation with performance superior to that of either subsystem (GPS or INS).