Part 3: Theoretical Core of Image Processing that Interprets Drone Imagery
Relative Orientation
In my previous articles, I’ve covered Interior orientation, Exterior orientation and in the continuation of the same I am writing this article on Relative Orientation.
Relative Orientation
This concept required the presence of two or more overlapping pair of aerial photographs. By a process called relative orientation, the two projectors on top of the two overlapping photographs are oriented so that it bears the exact angular orientation to one another as in the case when they were exposed.
Relative Orientation creates a miniature true 3D stereo model of the overlapped area. It determines the relationship between two images forming a model. At the instant when two photographs are taken from a stereo pair there will be an altitude and position relation between two photographs. Corresponding points in the images taken from two different cameras; can be used to determine the object in the scene, one has to determine the position and orientation of one camera with respect to another.
Along the flight direction consider 60% overlap and 20-30% overlap in lateral direction as per the standards of the photogrammetry. This percentage can be increased up to 80% for both the overlap to achieve accuracy.This is the classic photogrammetric problem of relative Orientation.
The internal geometry of the cameras, including its principal distance and the location of the principal point, ray can be constructed by connecting the points in the images to their corresponding projection center. These rays, when extended, intersect at the point in the scene that gives rise to the image points. This is used to determine the position of points in the environment. The two projectors are first positioned are in relative orientation to one another by estimation. Then using the tools of the stereo plotting instruments the various orientations are carried out to align the two imagery.
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