45-90 degrees from horizon. High Oblique -Horizon visible. 0 to 45 degrees from horizon. Unprocessed or raw imagery. Certain characteristics such as distance from sensor to target, terrain relief, and tonal patterns caused by varying light conditions or seasonality affect the usefulness of image products. Fortunately, post-image processing can adjust or correct many image problems.
Focal length affects apparent distance.
Correcting the imagery and mosaics Photo rectification removes scale distortion. Computers make this a simple task. Coverting from central perspective to parallel perspective results in an orthoimage or a corrected image. Digital orthophoto quads . To increase their usefulness requires a number of enhancements.