Orthorectification: Concept and Steps
The objective of this learning object is to explore both the concepts and practical steps involved in image orthorectification.
Ground features, resting at different elevations on the surface of the Earth exhibit positional displacements (disparities). This information can be used to make an image orthographic, with every point in its correct location relative to other points, regardless of elevation. The process of orthorectification produces an output in which all perspective distortion is removed and every point on the ground appears as if viewed from directly above. Through this process, the geometry of an image is preserved as planimetric by accurately modelling the nature and magnitude of geometric distortion. This is a kind of differential rectification process as it applies different amounts of rectification to selected sections of the photo (model).
The information required for orthorectification is:
- Exposure station attitude (omega, phi, kappa),
- Exposure station coordinates, and
- Object point coordinates