위치권 및 천체 방위를 이용한 진위 결정 알고리즘의 구현

Abstract

Most navigating ships calculate their positions depending on GPS. However, regarding the special situation, on a ship, the only alternative of GPS to calculate the position of the ship is Celestial Navigation until the present.

Positioning using celestial bodies has been used by using a sextant. Mostly, St. Hilaire method, using Almanac and Sight Reduction Table to calculate Altitude of Sun or using LOP to calculate the meridian line, has been used, which has difficulties because AP through DR is essential. Meanwhile, as IT technology develops, it is now possible to calculate the position of the ship by applying COP method, the virtual large circle concept, adding rapid processing capacity and accurate computing capacity of calculator. Although the recent method is accurate and convenient, it has the flaw which is generation of two positions due to intersections of two circles. In other words, one is True Position and the other comes to be False Position.

Therefore, in this study, the method to distinguish True Position from False Position is suggested. The altitude of celestial bodies is measured twice and the intersecting points of COPs using the GPs of celestial bodies are decided as the position of the ship, which is called Two-Body Fix method. As two intersection points of COPs are produced as an inevitable consequence, this thesis proposes a method to distinguish the True Position from False Position by sighting Azimuth of celestial bodies.

This method is premised upon geometry of sphericity, not interpretation of Euclidean surfaces. In this thesis, it is verified that the Great-circle on the sphericity is also 180 degree as well as a segment in the Euclidean surface is 180 degree. Moreover, both the segment connecting two GPs and the segment connecting two observer positions consist of Great-circle and it is also proved that these two segments cross at right angles by the Running Fix which has slight Dec fluctuation. It is unusual to have similar Dec values in Simultaneous Observation where the Great-circle connecting two GPs is not parallel to the equator. As the order of two GPs could changed, the algorithm is implemented by LHA comparison and by making the tilted Greatcircles diamond-shaped. Thus, it is classified to Running Fix and Simultaneous Observation by celestial body and time of sighting so that it is proved that the method used in Simultaneous Observation is possible to be used in Running Fix.

In other words, the relationship between two GPs and two observer positions is proved. To use Azimuth in particular, the rationale of this thesis is provided by two manners: simulations and tests.

In the absence of GNSS, True Position determination method using Azimuth of celestial bodies suggested in this thesis of automatic position calculation using Celestial Navigation is appliable as an alternative. Then the method is considered to be used to apply and develop safe and efficient marine transportation system.