Abstract: On the basis of direct georeferencing in POS-supported aerial photogrammetry，the relationship model between accuracy of object points and exterior orientation elements is established according to the error propagation law.The accuracy requirements of exterior orientation elements in topographic mapping are analyzed in theoretically.Four sets of actual aerial photos are used to test；which are at different scale and in different terrain.The empirical results verify that image elements of exterior orientation obtained by a POS can satisfy the accuracy requirements of topographic mapping，no matter which scale and terrain the empirical block is classified to.However，to satisfy the accuracy requirements of object point in elevation，the accuracy requirements of exterior orientation elements are at least one time higher than that in planimetric mapping.

Key words: Position and Orientation System（POS）, exterior orientation elements, direct georeferencing, aerophotogrammetric mapping using image orientation parameters, accuracy

摘要： 基于POS辅助航空摄影测量直接对地目标定位理论，根据误差传播定律建立了物方坐标精度与影像外方位元素精度的关系模型，并从理论上分析了各种基本比例尺地形测图对影像外方位元素的精度需求。通过对摄自不同地区、多种摄影比例尺航摄影像的实验表明，由POS系统获取的影像外方位元素进行安置元素测图完全可以满足各种比例尺、不同地形图测绘的精度要求，但为了满足地物点的高程精度，对影像外方位元素的精度需求较用于平面测图时的至少要高出一倍以上。

关键词: POS系统, 影像外方位元素, 直接对地目标定位, 安置元素航测成图, 精度