【正文】 rated system (also called POS) to acquire a photo’s position and attitude (., to obtain exposure station’s position by GPS, and images’ attitude elements by IMU), for the purpose of photo orientation, and the final goal is to replace block aero triangulation procedure[49]. Modern digital photogrammetry will play an important role in automated productions of 4D products (DEM, DOM, DLG, DRG) and updating of spatial databases. This paper will introduce current operational applications of aerial photogrammetry and related technical requirements, in particular, geometric positioning accuracy obtainable in the photogrammetric information chain from photo orientation to stereomodel reconstitution, aiming to investigate their practicability for 4D products production. It is hoped that findings from this study will provide guidance for operational aerial photogrammetry in the context of national land surveying, mapping, and fundamental geographic information acquisition. 1 Current patterns of the modern aerial photogrammetry Nowadays, there are primarily three patterns for aerial photogrammetry, namely, standard aerial photogrammetry, GPSsupported aerial photogrammetry and POSsupported aerial photogrammetry. Their main procedures are shown as . Flowchart of the modern aerial photogrammetryFrom , we can learn that the main difference between these three patterns lies in the ways of aerial photo acquisition and photo orientation. For standard AT, it is through block aerotriangulation with a large number of GCPs to get a model orientation points’ coordinates to plete image orientation. For GPSsupported AT, in aerial photo acquisition process, dynamic GPS positioning is used instead of GCPs to determine the positions of exposure center and meanwhile obtain the model’s orientation points’ coordinates, which are then used to rectify the image’s orientation. For POSsupported AT, images and their corresponding orientation elements (six exterior orientation elements of images) are both acquired, in order to realize geometric inversion of photography by storing their spatial positions and attitude at the moment of exposure. 2 Related technologic requirements Aerial photography In modern aerial photography, in order to improve the quality of obtained images, besides adding flight control systems to aerial camera (such as ASCOT, CCNS4, Aerial TRACKER system), the methods include sticking a GPS receiver with the camera firmly when adopting GPS aerial photography and mounting POS system on the camera in DGPS/IMU aerial photography. According to the different patterns of aerial photography, we can formulate an answerable plan as YUAN Xiuxiao/On Stereo Model Reconstitution in Aerial … 237shown in . Ground control plan In digital photogrammetry workstations, aerotriangulation is carried out by the most theoretically rigorous procedure of bundle block adjustment, but for the sake of obtaining the best pass points’ coordinates and the exterior orientation elements of photos, ground control plan should be designed, as shown in , for different patterns of aerial photogrammetry. Patterns of the modern aerial photography Distribution of GCPs in bundle block adjustment Digital mapping Theoretically, after getting the accurate exterior orientation elements of images, measurable stereo models can be reconstructed using model restoration, by which we can do surveying and mapping of terrain and objects automatically. However, the current process of producing 4D product is: single photo interior orientation → relative orientation of stereo pair → single model absolute orientation → surveying and mapping on stereo models. The method of model restoration is only adopted in the direct georeferencing of POSsupported aerial photogrammetry. 3 Experiments and analysis There are two ways of aerial photogrammetric positioning. One is called block aerotriangulation, regarding image points’ coordinates, GCPs’ coordinates and/or the exterior orientation elements of images as weighted observed values, and bined bundle block adjustment is performed to solve the images’ orientation parameters and target points’ spatial coordinates, so as to supply orientation control points for stereo model mapping and do highly accurate geometric positioning. For aerial photogrammetry of different scales and topographic types, topographic maps specifications for aerophotogrammetric office operation has defined respective aerotriangulation method, ground control plan, and also concrete standards for pass point accuracy. This method is established and widely used. The other is called direct georeferencing, under the supposition that highly accurate image elements of exterior orientation were available, space intersection is carried out to calculate corresponding object point’s object space coordinates by using photo coordinate system’s coordinates of conjugative image points in stereo pairs. This approach directly determines the object’s position, so 4D products can be produced. Then the paper will mainly discuss how well the positioning accuracy can be achieved and the stereo model Yparallax when using image exterior