Orthorectification

Orthorectification is the process of removing the effects of image perspective (tilt) and relief (terrain) effects for the purpose of creating a planimetrically correct image. The resultant orthorectified image has a constant scale wherein features are represented in their 'true' positions. This allows for the accurate direct measurement of distances, angles, and areas (i.e. mensuration). Orthorectified images are commonly used as in visualization tools such as Google Earth, OSSIM Planet, ArcMap, WMS, etc.

The requisite inputs for orthorectification:

1. An image with accurate sensor geometry
2. A elevation model of the ground surface in DEM, DTED, or SRTM format

The resulting accuracy of the orthoimage is based on the accuracy of the triangulation, the resolution of the source image, and the accuracy of the DTM.