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Improving Image Positioning
The process of improving image positioning for project data starts with fine-tuning the calibration parameters for all cameras of the mission. This part is very similar to the Camera Calibration workflow. Usually, the camera file that is the result of the camera calibration is a good starting point for processing project data. However, it is most often necessary to adjust the camera parameters to the actual project imagery. If the calibration values are good, the fine-tuning should not be a big issue.
The second part of image positioning improvement adjusts the individual images based on a large number of tie points per image. The process is usually called aerotriangulation and effects the misalignment angle values of the images themselves. Normally, this is done for airborne imagery. Mobile ground-based images can be adjusted only with the help of TerraMatch functionality.
The adjustment of image positions requires that the camera parameters are good and stable for the project data.
Finally, the absolute accuracy of the images can be verified and possibly improved with the help of ground control points (GCPs). For airborne imagery, the GCPs are utilized to determine a systematic xy shift. The calculated shift values can then be used in a linear transformation applied to the images.
For mobile system imagery, the GCPs are also useful to derive fluctuating drift values for individual drive paths. These values are used by TerraMatch in order to compute fluctuating corrections. More information can be found in the TerraMatch Users Guide available at the Terrasolid webpage.
GCPs are placed in TerraPhoto as Known xyz, Known xy, or Known depth tie points. They must be entered manually in images that see the GCPs’ locations.