Because of sensor own characteristic limit, or in interference situation, the target information obtained is incomplete, in order to take full advantage of those incomplete information, an idea of target coordinates information-processing is presented. The cotangent relations theorem is given, and other theorems and the deduction application methods are summarized and compared, many useful algebraic formulas are inferred, pure information processing principles, are obtained, on azimuth, pure elevation angle and pure distance from the theory principle, then the target tracking problems are solved. Using this principle method means taking a great stride in realizing the information fusion project. Contrasting the geometry theorems and deductions of several similar graphs, summarizing these algebraic relations and applying both of them to the air defense information fusion are of important theoretic significance.