【正文】 Beijing: Publishing House of Surveying and Mapping [15] Yuan Xiuxiao, Fu Jianhong, Yan Peili, et al.(2020) Analysis of vertical parallax of stereo model reconstructed by using the elements of exterior orientation from position and orientation system [J]. Geomatics and Information Science of Wuhan University, 32(6):489493 。 Mapping Aviation Remote Sensing Co. Ltd and so on. These supports are gratefully acknowledged. The author would like to express his hearty gratitude to Fu Jianhong, Xie Chou, Ji Shunping and Yang Ming for participating in partial experiments. The author would like to thank Yang Ming and professor Zhang Jingxiong for their polishing in English. References [1] Li Deren, Shan Jie (1989) Quality analysis of bundle block adjustment with navigation data [J]. Photogrammetric Engineering and Remote Sensing, 55(12):1 743 1 746 [2] Ackermann F (1994) Practical experience with GPS supported aerial triangulation [J]. Photogrammetric Record, 16(84):861874 [3] Yuan Xiuxiao (2020) The principle and application of GPSsupported aerial triangulation [M]. Beijing: Publishing House of Surveying and Mapping (in Chinese) [4] Cannon M E, Sun H (1996) Experimental assessment of a nondedicate GPS receiver system for airborne attitude determination [J]. ISPRS Journal of Photogrammetry amp。 POS photogrammetry can be used for the production Geospatial Information Science 11(4): 235242 242 of orthophotos and update of 4D products in small regions. However, POS has a promising prospect in the field of largescale urban mapping, LIDAR, and digital aerial photogrammetry. We should promote the integration technology of POS system and other sensors by undertaking large scale experiments, thus providing technical support for economical and rapid gathering of geospatial information. Acknowledgement The experiment data acquisition are supported by Institute of Remote Sensing Applications Chinese Academy of Sciences, Zhong Fei General Aviation Company, Liaoning Jingwei Surveying amp。 POS direct georeferencing is one of the important cuttingedge techniques in photogrammetry. The basic spatial information acquisition should take advantage of this, and design good plans to gain maximum financial benefits. We propose that, for largescale mapping of flat areas with good transportation, standard AT should be employed primarily。 but the accuracy of the photo’s angular elements has nothing to do with the photo scale but is related to the focal length of the camera, so the shorter the focal length is, the higher the photo’s angular elements accuracy is. Additionally, by paring the data in Table 2, it can be found that the exterior orientation elements provided by POS system perform are worse than that of analytic aerotriangulation, and also obviously worse than the POS nominal accuracy ,XYZmmm=== 18 , 36mm m?ω κ′′ ′′== =. Accuracy of direct georeferencing Currently, 4D product monly uses the densified points acquired by aerotriangulation as the model orientation points instead of reconstructing the stereo Geospatial Information Science 11(4): 235242 240 model directly from the image exterior orientation elements. So the accuracy requirement of exterior orientation elements is not defined in the current norm. Generally speaking, so long as enough densification points meet the error threshold limit for each model can we get, by performing absolute orientation, a measurable model which can be reconstructed. Then we can acquire satisfying spatial information. We analyzed the accuracy of direct georeferencing by using different exterior orientation elements, which is calculated by the approach that firstly employ forward intersection[14], by using the six exterior orientation elements with different accuracy obtained in the above section, to pute the ground coordinates, and calculate the RMS of ground coordinates of object points (seeing Table 3 for detail) by paring the ground coordinates with those of most GCPs.Table 3 Accuracy of direct georeferencing Maximum discrepancy/m Minimum discrepancy/m RMS/m image Method to acquire EO Num of check points X Y XY Height X Y XY Height X Y XY Heighttest 1 Std. 188 GPS 196 POS 196 test 2 Std. 412 GPS 419 POS 419 test 3 GPS 68 POS 64 test 4 Std. 46 GPS 46 POS 46 From Table 3, such conclusions can be summed up as follows: 1) For test 1, the horizontal accuracy of direct georeferencing is better than meter and vertical accuracy better than meter, which well meet the requirement specified in 1:500 flat land terrain mapping standards: meter in plane and meter in elevation[11]. 2) For test 2, the horizontal accuracy of direct georeferencing is better than meter and vertical accuracy better than meter, which well meet the requirement specified in 1:500 mountain terrain mapping standards: meter in plane and meter in elevation[11]. 3) For test 3, the horizontal and vertical accuracy of direct georeferencing are both better than meters, which well meet the requirement specified in 1:5000 t