Abstract
The methods of determining a ship’s position in terrestrial navigation by using vertical and horizontal angles are nowadays rarely used. The reason is the relative complexity of the procedure and the lack of accuracy of some methods. Different methods of using horizontal and vertical angles to obtain the line of position (LOP) will be presented in this paper, as well as the occurring errors and recommendations for use. In this paper, the sextant will be considered a basic instrument for measuring horizontal and vertical angles. The sextant allows a very precise measuring of angles from which very accurate lines of position can be obtained.
Highlights
A horizontal angle can be obtained as a difference between two bearings or two relative bearings
The sextant is a primary instrument for celestial navigation, i.e. instrument designed to measure the altitudes of celestial bodies above the visible sea horizon
The sextant allows us to measure the vertical angle of terrestrial objects as well as horizontal angle between two points
Summary
A horizontal angle can be obtained as a difference between two bearings or two relative bearings. The sextant makes the obtainment of very precise vertical and horizontal angles possible, the final accuracy of the associated line of positions will be different. The main reasons are: the influence of the dip of the sea (or shore) horizon, error in the height of the observer’s eye and error in the height of the observed object These errors have to be taken into consideration during the measurement of the vertical angle. There are methods for obtaining the line of position by using a vertical angle if the height of the objects is unknown. These methods will be explained in further text. LOP from a horizontal angle ( α ) determination of the radius (r)
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