【正文】 rds, the exterior orientation elements derived from that can be used absolutely for producing 4D product. YParallaxes in reconstituted stereo models In the work of photogrammetry, another issue we should pay attention to is the feasibility of directly reconstructing the stereo model for terrain mapping YUAN Xiuxiao/On Stereo Model Reconstitution in Aerial … 241with exterior orientation elements used, that is Yparallax of model point is not beyond 20 m[1113]. So three stereo pairs depicting different terrain types are chosen from four tests respectively to reconstruct stereo model using the obtained exterior orientation elements[15], and Table 4 is the Yparallax on stereo model’s corresponding points. From Table 4, it can be seen that when using the exterior orientation elements obtained by the method of aerotriangulation to reconstruct stereo model, no matter what type of terrain is applied and how much the scale is, the model points’ maximum Yparallax lies in one pixel and the RMS of that is below half a pixel, which satisfies the accuracy requirement of terrain mapping that vertical parallax’s RMS of each model should not be beyond 20 m. But when we use the exterior orientation elements provided by POS, the vertical parallaxes of each model point are all slightly larger, and the smaller the photo scale, the larger the vertical parallax, pletely not meeting the requirement.Table 4 YParallaxes of stereo models reconstructed by exterior orientation elements Yparallax/μm Maximum Minimum RMS Image Model Pts Maximum height difference /m Regular GPS POS Regular GPS POS Regular GPS POStest 1 282/281 23 274/273 32 343/344 27 test 2 14/13 26 29/28 47 275/274 34 test 3 1017/1018 31 1013/1014 22 234/233 54 238/237 23 test 4 1076/1075 32 1115/1114 28 1105/1104 28 4 Conclusion It can be shown from the experiment that, if the elements of the exterior orientation obtained from aerotriangulation meet the accuracy standards, they can be used directly for image orientation and stereo model reconstitution. However, because of systematic errors in POS exterior orientation elements, it is currently difficult to meet the standards of photogrammetry, especially when extracting 3D spatial information. It was found that, in the time of digital photogrammetry, much work can be done automatically by puters, with the reliance on GCPs lessened gradually, thus simplifying operational photogrammetry. On the whole, standard AT, which is the most established and widelyused approach to obtain image orientation parameters, is still the main body of photogrammetry。 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。 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 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。181。m Hori. Verti. Hori Verti X Y XY Z Xs/m Ys/m Zs/m φ/(″) ω/(″) κ