Write an essay on Geo-referencing.

Scanned roster images and satellite imageries are corrected for distortions by matching them with ground control points (GCPs) occurring in an image. GCPs are features of known ground location that can be accurately located on the aerial photo or satellite imagery. GCPs are located both in terms of their image coordinates (columns and row numbers) on the distorted image and in terms of their ground coordinates (typically measured from map or established on the ground in terms of latitude and longitude with respect to a particular projection system say polyconical). A least square regression analysis is done to interrelate the geometrically correct (map) coordinates and distorted image coordinates. Then image is worked to have correct geometrical relationship with its corresponding ground situation.