If landmarks such as street intersections are absent, panels are set out at known pre-surveyed locations on the flight path. Panels appear as cross marks on the photo. Radar is lower resolution but can penetrate clouds. Edge match pair and align correctly Compensate for distortion in image by using principle point and adjusting for shift and other distortion. Use stereoscope, zoom transfer scope or digital methods to detect topographic relief Photogrammetry is now an automated process.
More control points greater precision.
Can be inaccurate since computers cannot think thus mistake canopy for ground surface, etc. What you think you see is not always what you get. The implies need for ground truthing Topographic mapping most common application. Looking at many photographs develops ability to interpret, but some creativity and imagination is handy. 10 Minute Break.