| 摘要 |
PURPOSE:To perform an easy and rapid finding of a direction at a given point on a globe, such as meccas, by a method wherein an isogonic curve line, based on an directional angle against a magnetic needle at an optional point from a given point on a globe, is computed for drawing on a map. CONSTITUTION:A spherical angle beta of a spherical triangle, which is formed with a large circle A, consisting of a given point M, such as meccas, and a north pole N, a large circle C, consisting of the points M and N, is computed to conduct a correction based on a magnetic needle displacement angle gamma at the point X, and a direction angle alpha of the point X to the point M is then decided. Through the computation of said direction angle alpha in relation to each point, an isogonic line, based on the point M, is drawn on a map. Thus, the map is cut in as a brochure, and a direction indicator, providing with a magnetic needle on a clear base plate, easily and promptly performs a finding of a direction at a given point, such as meccas, corresponding to the directional angle of the isogonic curve line on the map through a direction indicated by the magnetic needle. |
