A Distance Measuring Method on Polar Stereographic Charts Based on Equidistant Circles

An exact and simple method for measuring distance on polar stereographic nautical charts used for polar navigation is investigated. Equations for thumb lines and great-circle lines were deduced;shape analysis results indicate that great-circle distance is preferable for distance measuring in polar navigation. Formulas for calculating the distance of straight-line segments on polar stereographic charts based on their geometry are given as distance difference analysis results indicate that measuring distance by straight segments is feasible. Moreover, an exact and simple distance measurement method based on equidistance circles is presented based on the fact that small-circles on earth can be projected into circles on polar stereographic charts. The proposed method can satisfy the polar navigation application requirements for polar stereographic charts.