双等距离投影及其应用

双等距离投影是指自图上两定点出发至图上任意点间的距离都与实地等长的投影。本文先从球面极坐标出发，讨论了双等距离投影公式的建立，继而给出了在地理坐标下的正轴和斜轴投影计算方法。本文证明了该投影的性质属任意投影，其计算方法是可行的，有实用价值。双等距离投影在测量上可用于圆圆系统定位，在军事上可用于敌情监测等。

DOUBLE EQUIDISTANT PROJECTION ANDIT'S APPLICATION

: Double Equidistant Projection is the projection, on which, two geodetic lines betw een two fixed positions and any position on the earth are projected as two straight lin es, and the lengths of the two lines projected-to the actual distances are equal proporti onal. In this paper, the formulas of Double Equidistant Projection are firstly derived from the polar spherical. Then the algorithms are presented using geographical coordin ates for both oblique or normal projections. The characteristics of Double Equidistant Projection is proved to be aphylactic. It is possible to draw a projection net with the formulas in the paper, so they can be used in practice. Double Equidistant Projection can be used in positioning with a circle-circle system on surveying, and militarily, in monitoring of the enemy's situation, etc.