Terrestrial navigation
Terrestrial navigation cannot be defined in a rigorous manner. The heterogeneous techniques and methods make it difficult to define a unique classification. Throughout this book, the notation terrestrial navigation is applied to all techniques that are ba
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Introduction Definitions
Terrestrial navigation cannot be defined in a rigorous manner. The heterogeneous techniques and methods make it difficult to define a unique classification. Throughout this book, the notation terrestrial navigation is applied to all techniques that are based on terrestrial sightings and/or measurements; however, radio navigation systems are not included. Terrestrial navigation comprises dead reckoning, visual navigation, and some other generic position fixing techniques. These methods are applied in land, maritime, and aeronautic applications. Dead reckoning (DR) means relative positioning with respect to previous positions. It requires the repeated determination of distance sections traveled and the respective directions of the distance sections. The origin of the term dead reckoning is disguised. There are two opposite assumptions. One states that in seafaring, the reckoning is done for "dead" water, i.e., without considering current. The other suggests that dead (or rather "ded") reckoning is an abbreviation for deduced reckoning. Despite of its roots, the notation has been used over centuries in the English tongue. In marine and aeronautic navigation, DR is complicated by wind and/or current, leading to a drift of the vessel or aircraft. The effect of drift must be accounted for to keep up an estimation of the actual position of the craft. Due to the nondeterministic character of drift effects, the positions obtained by DR are corrected by position fixing (i.e., absolute positioning) whenever possible. Visual navigation corresponds to fixing positions (i.e., coordinates referring to a well-defined reference frame) with respect to known and visible landmarks. It is based on the use of maps and involves measurements performed with instruments. Visual navigation is mostly applied in maritime applications where optical instruments may be used during most phases of a voyage of a vessel. A specific technique of visual navigation is piloting (or pilotage). The meaning of piloting differs between marine and aeronautic navigation. In case of marine navigation, piloting means "navigation involving frequent or continuous determination of position relative to observed geographical points, to a high order of accuracy". A vessel pilot has exceptional knowledge of difficult or restricted waters and is usually no permanent member of the ship crew (National Imagery and Mapping Agency 1995). In B. Hofmann-Wellenhof et al., Navigation © Springer-Verlag Wien 2003
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6 Terrestrial navigation
aeronautic navigation, piloting means determining locations in terms of topological relations with visual reference to known and visible landmarks. In any case, piloting involves the use of charts. All visual navigation techniques require a proper visibility of terrestrial objects, i.e., the weather conditions must allow sightings and/or measurements to landmarks. Finally, generic terrestrial position fixing also involves measurements performed with nonvisual instruments. Examples of nonvisual instruments are spee
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