7.3.3 Rotation

Rotation of one image with respect to the other can be useful when the images are acquired over far northern or southern latitudes (greater than 60 degrees) or, when an opposite side stereo configuration is used to make up the stereo pair. For example, the right hand image of Stereo pair 1 has been rotated with respect to the left-hand image using digital image analysis software.

Bathurst Island is at latitude 75 degrees North. In order to rotate the right hand image, common control points along the coastline were collected. The right hand image was then registered to the left using a first order polynomial transformation and a bilinear resampling kernel. This results in a right hand image that can be horizontally aligned with the left-hand image. Manual rotation is no longer necessary.

In contrast, as the geographical location is just south of the Equator, the imagery of the Tapagos Forest, Brazil (Stereo pair 11) lines up without any manual rotation.

Another example of imagery that could be digitally rotated in order to improve stereo viewability by eliminating the need for manual rotation is Stereo pair 17. Although this imagery of Indonesia is located at just 2 degrees South of the Equator, it has been acquired on an ascending and a descending pass. This causes the resulting two images to be rotated with respect to each other.