Approximate direct georeferencing in national coordinates
Approximate direct georeferencing in national coordinates
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DOI：
10.1016/j.isprsjprs.2006.02.004
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发表时间：
2006-06
影响因子：
12.7
通讯作者：
K. Legat
中科院分区：
文献类型：
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作者：
K. Legat
在摄影测量和遥感中，直接地理配准越来越重要。由此，由GPS/INS确定图像传感器的外部定向（EO）的参数，产生在全球地心参考系中的结果。然而，国家大地测量基准往往需要数字地形模型或正射影像等摄影测量产品，并通过国家地图投影绘制，“国家坐标”。由于摄影测量的基本数学是基于笛卡尔坐标的，因此场景恢复通常在位于图像块的某个中心位置的笛卡尔框架中执行。随后转换为国家坐标是大地测量学中的一个标准问题，并且可以以严格的方式完成-至少如果地图投影的公式是严格的。这个过程的缺点包括与摄影测量处理相关的实际缺陷以及转换整个场景的计算成本。为了避免这些问题，本文追求一种替代的处理策略，在恢复之前转换EO参数。然而，如果只进行这种转换，场景就会被系统地扭曲。原因是由于地球曲率和地图投影不可避免的长度失真，国家坐标不是笛卡尔坐标。为了解决这些扭曲，需要进行几项修正。这些都是被动和主动成像详细处理。由于所有这些校正都只是近似值，因此所得到的技术被称为“近似直接地理配准”。尽管如此，残余失真通常是非常低的，如模拟所示，使该技术成为一种有吸引力的直接地理配准方法。
Direct georeferencing has gained an increasing importance in photogrammetry and remote sensing. Thereby, the parameters of exterior orientation (EO) of an image sensor are determined by GPS/INS, yielding results in a global geocentric reference frame. Photogrammetric products like digital terrain models or orthoimages, however, are often required in national geodetic datums and mapped by national map projections, i.e., in “national coordinates”. As the fundamental mathematics of photogrammetry is based on Cartesian coordinates, the scene restitution is often performed in a Cartesian frame located at some central position of the image block. The subsequent transformation to national coordinates is a standard problem in geodesy and can be done in a rigorous manner–at least if the formulas of the map projection are rigorous. Drawbacks of this procedure include practical deficiencies related to the photogrammetric processing as well as the computational cost of transforming the whole scene. To avoid these problems, the paper pursues an alternative processing strategy where the EO parameters are transformed prior to the restitution. If only this transition was done, however, the scene would be systematically distorted. The reason is that the national coordinates are not Cartesian due to the earth curvature and the unavoidable length distortion of map projections. To settle these distortions, several corrections need to be applied. These are treated in detail for both passive and active imaging. Since all these corrections are approximations only, the resulting technique is termed “approximate direct georeferencing”. Still, the residual distortions are usually very low as is demonstrated by simulations, rendering the technique an attractive approach to direct georeferencing.