Optimal Diameter of Circular Object Targets for Photogrammetric 3D-Measurement and Camera Calibration

The use of circular object targets is very common for an optical 3D-measurement and camera calibration. An object circle is projected on the image plane as an ellipse, if the object plane and the image plane are not parallel to each other. The image coordinates of the center of the ellipse and the true coordinates of the projected center of the ciruclar object target are not identical resulting in systematic geometric image measurement errors (eccentricity). This paper describes the functional context of this eccentricity for a general target/camera setup. Possibilities for a correction of this systematic eccentricity error are derived. A guideline for the proper combination of object target sizes and exposure distances guaranteeing reliable image point measurements and accurate object point determination are proposed.