Orthorectification is the process of correcting the imagery for variation in the position of the sensor/platform, for convergence of light, for distortion due to curvature of optical lenses and for irregularity in the terrain. Orthorectification is a form of geometric correction that takes into account the relief of the terrain. Orthorectification involves the removal of distortions introduced into remote sensed imagery caused by changing terrain elevations, sensor location & the earths curvature and requires the availability of a suitable digital terrain model & ground control points.