Method for the correlation of three dimensional measurements obtained by at least one first (1) and one second (2) image capturing unit. The method comprises, for the calibration phase, the steps of: producing a calibrating ball (4) movably and rotatably mounted about an axis (7), successively and rotatingly shifting the calibrating ball (4) into the measuring positions which are visible to the acquisition units; measuring, for each of the measuring positions, the spherical cap seen by each of the image capturing units; determining, for each of the measuring positions, the center of the calibrating ball, to express the same reference frame in the first and second reference marks viewed by the first and second image capturing units respectively; calculating the matrix of the passage from the first reference mark to the second reference mark to correlate the measurements between the first and second optical image capturing units.
A flying sphere is photographed twice at a predetermined time interval and two static images thus obtained are used to measure a rotation of the sphere through an image processing based on a recognition mark of a surface of the sphere. The recognition mark includes a central mark having a directivity and a rotating angle calculating mark provided to surround the central mark. The central mark includes a rectangle and a circle provided apart from the rectangle adjacent to one of short sides of the rectangle. Three or more rotating angle calculating marks are provided. Respective center positions of the rotating angle calculating marks are present in a region provided apart from a center position of the central mark by 13 mm to 17 mm.
A sphere having a plurality of marks given to the surface thereof is photographed at a plurality of times to obtain a plurality of two-dimensional images of said sphere. An imaginary sphere having a plurality of marks given to the surface thereof is generated in a three-dimensional coordinate space by a computer. In making the imaginary sphere placed in a reference posture coincident with the posture of the two-dimensional image, an optimum displacement amount of said posture of said imaginary sphere is determined by using a computation based on Genetic Algorithms. A rotation matrix is derived from the posture of the sphere measured for each dimensional image thereof and a computation is performed on the rotation matrix to thereby obtain the rotational amount of the sphere and the direction of its rotational axis.
