You take a sphere, in 3 dimensions, you rotate around the centerof the sphere, and all those rotations leave the sphere alone.
那一个三维的球来说,无论你怎样把它绕中心旋转,它都会保持不变。
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As to software design, we adopt Hough transform theory to calculate the coordinate of the ball's center in order to work out the velocity, by the way of edge detecting of the sphere.
The image of sphericity which does not located the principal optic axis is an ellipse based on pinhole model, and the image center offsets from the projection of the spherecenter.