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A key component of this system is the identification and removal of all lens distortion and asymmetry from the image as if these issues are not dealt with it is impossible to accurately match the photograph to the survey data and CGI elements.
A sophisticated photogrammetry based calibration system is therefore employed to recover all camera and lens parameters and distortion characteristics which is then used to remap the image into a perfectly symmetrical 2d projection ready for the alignment process.
These calibrations are carried out at different lens offset points to account for fully corrected images even when lens shift is applied as can be seen below (distortion values are for illustration and not the actual ones for the lens)
The corrected image is placed in a pre prepared template and positioned so that the optical axis on the image is aligned with the center of the background. This creates the symmetrical background for the subsequent camera alignment and 3ds Max processes. Data for the key image parameters are displayed in a text box and survey points are marked up on a separate layer. With this system survey points at the outer edges of the image can be used as these have the largest angular convergence which increases the accuracy of the the alignment process.
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