What term refers to the point on an aerial photo that falls midway between the principal point and the nadir point?

The term that refers to the point on an aerial photo that falls midway between the principal point and the nadir point is known as the isocenter. This point is significant in aerial imagery because it represents a location where the distortions of the image are minimized, providing a more accurate representation of the ground features. The principal point is where the camera's optical axis intersects the ground, while the nadir point is directly below the camera. The isocenter effectively balances the effects of tilt and obliquity in aerial photography, making it crucial for photogrammetric calculations and ensuring accurate measurements can be taken from the image data.