Measuring the Scale of a Point on Airphoto

Airphoto is center\|projectioned, which has a lot of errors, mainly involving projection distance, tilt and projection difference, compared with orthorectified projection system. These errors result in scale difference in airphotoThe more the errors have, the more different the scales have. These errors greatly hinder the airphotos' application. So how to measure airphoto scale is the key of airphoto application. Normally, the scale of airphoto includes main scale, average scale and point scale. This paper discussed how to measure any point scale in airphoto in detail after calculating main scale and average scale. The results of studying area showed that when the elevation difference is 47.5 m, the scale difference is 5.7%, when the elevation difference goes up to 100 m, the scale difference is up to 12.9%; The main scale is poorest, and the average scale has good accuracy but is only adapted to smooth areas, and point scale can be used to calculate scale of any point in airphoto and also has good accuracy.