Orientation quality & Aerotriangulation
The aerotriangulation process results in image orientations which consist of camera position, rotation, and interior camera parameters (focal length, principal point, distortion parameters).
Together with the images, image orientations serve as input when creating a SURE project. Their accuracy reflects strongly on the quality of the results.
Ensuring high-quality orientations leads to:
Higher geometric accuracy
Below you will find some best practices regarding the aerotriangulation process:
Ensure a parallax below one pixel for all images (nadir, oblique, etc).
Do not use data retrieved from GPS/INS alone. Use Aerotriangulation, Structure from Motion, or Bundle Adjustment software instead to refine the navigation data.
Make sure that tie points are matched in every image for ensuring sub-pixel parallaxes.
Use a stereo viewer for assessing the quality of the orientations (parallax / vertical shift/perpendicular to epipolar direction).
Avoid using only the relative orientation of the camera rig (tie points only in nadir images, etc.). Tie points should also be matched in oblique images.
Ensure that images have enough tie points between each other. Also images of different viewing directions. Low sigma-naught values are a good indicator of orientation precision only when they are based on a high number of tie points.
Use automatic tie/feature points for improving the relative accuracy of the orientations.
Use ground control points for improving the absolute accuracy of the orientations.
Use a high number of ground control points when also estimating the interior parameters of the cameras (mostly the case for close range- and UAV- mapping).
For pre-calibrated metric cameras with sub-pixel interior orientation accuracies, use enough ground control points for ensuring proper absolute accuracy.
Use ground control points not considered during the adjustment as independent check points for quality assurance purposes.
Ensure that the accuracy of ground control points is at least four times higher than the desired accuracy for the whole block.
Ensure that enough ground control and check points are well distributed across the entire project area.
If in doubt, contact your software vendor and ask how to achieve the recommended settings.
SURE will still work with low-quality orientations, but the results will be affected negatively. Low-quality orientations could lead to noisy surfaces, lack of geometric detail, and round edges.