高緯度における位置の線(II)(日本航海学会第16回講演会)

抄録

In the last paper, we treated the errors of line of position that is plotted on the Mercator's chart and found that the error due to the convergency of meridian was most severe for the high latitudes. At this paper, in order to exclude this error, we get the stereographic projection from the conditions of conformality for polar representation. We investigate the characters of the errors of line of position on this projection arising from: (i) the length of intercept taken from the latitude graduation, (ii) the position of the terminal of intercept plotted as straight line, (iii) the azimuth of position line plotted perpendicular at the terminal of straight line intercept, and (iv) the line of position as approximation of the circle of position. The resultant effect to the fixed position is sufficiently small for the ordinary air or surface navigation at higher latitudes, for example, less than one mile for latitude 80°, and less than four miles even for latitude 60°. For the polar navigation, we adopt the pole itself as an assumed position and can easily plot the line of position without computation. A simple correction table for the curvature of position line is provided, which can be used for the whole polar region higher than latitude 85°.