Determining image distortion and PBS (point of best symmetry) in digital images using straight line matrices

•Measurements in photogrammetry require removing image distortion.•We determine radial and tangential distortions and PBS (Point of Best Symmetry).•We only measure point coordinates regardless of the position and direction of lines.•Points belonging to multiple lines are optimal (not a problem).•Results are optimal even using a single image with a minimum number of observables.

It is impossible to take accurate measurements in photogrammetry without first removing the distortion in images. This paper presents a methodology for correcting radial and tangential distortion and for determining the PBS (Point of Best Symmetry) without knowledge of the interior orientation parameters (IOPs). An analytical plumb-line calibration method is used, measuring only the coordinates of points on straight lines, regardless of the position and direction of these lines within the image. Points belonging to multiple lines can also be used since the effects on their X and Y coordinates are calculated independently. The results obtained on an image of a common scene, taken with a handheld non-metric camera, show a high degree of accuracy even with a minimum number of observables. And its application on a calibrated grid for engineering purposes with a semi-metric camera, results optimal even using a single image.

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