Because the aerial imagery is acquired by the way of vertical photography, the banking angle is very small, almost closing to zero, and the inner element is known.
由于航空遥感影像近似竖直摄影的特性，倾斜角非常小，几乎接近于零，而且内方位元素已知。
2
In a general way, aerial image is not orthograph, most buildings exist slope Angle as well as vertical lines in aerial images.