中文摘要：

研究了应用线特征进行摄像机位姿测量的三线透视问题（P3L）在三条直线共面并成门形摆放时的闭式解问题，研究了该种情况下解的特性，得出当摄像机光心位于过三条直线的两个交点且垂直于三条直线的平面时，该问题存在无穷多解，当光心不在此平面时则存在唯一解，应用几何方法给出了该结论的证明，给出闭式解求解方法，对该方法进行的计算机仿真证明了方法的正确性，该方法对实际应用有一定的指导意义。

英文摘要：

The perspective-three-line problem （P3L） when three hnes are coplanar and placed as door shape is studied for camera pose determination. The solution of the problem has following prop- erties： if the camera＇s optical center locates on the plane which is perpendicular to the three lines and passes the intersection points of the three lines, for the problem, exist infinitely many solutions, otherwise exist only one solution for it. The properties are proved by geometric methods and a closed-form solution is proposed. The simulation proves that the method is correct. The method can be applied to pose measurement systems.