Orthorectification corrects an image for terrain and distortions inherent in cameras or digital scanner platforms. It is the only reliable way to ensure that all pixels in an aerial or satellite image are systematically corrected to the ground. In order to orthorectify, a sensor or camera model must be available, and a digital elevation model of the area to be corrected must exist. In order to produce results with respectable degree of spatial accuracy, a source of ground control must also be used. Ground control can come from other orthoimagery, maps, vectors, or GPS-surveyed points. The accuracy of the final product is directly related to the accuracy of the sensor model, the ground control, and the DEM.  When several scenes are involved in an ortho project, the accuracy of the result can be improved through tie points and a block bundle adjustment. Our expertise in this area helps us choose appropriate inputs, use advanced orthorectification software, and give our customers realistic expectations of what they will receive.