points of the ellipses in fig5 fig7 illustrates a position relation of the points on the straight line in fig6 and fig8 shows projected concentric circles and its supporting plane n 1 and n 2 represent calculated normal vectors from ellipses c 1 and c 2 using incorrect estimates of the intrinsic parameters as shown in fig3 a concentric circle pair located in a 3d space has the following geometric conditions 1 the center of the two circles are located at the same coordinate 2 the two circles are located in the same plane 3 the radiuses of the two circles are different an image of the concentric circle having this geometric structure is taken using a camera meanwhile a concentric circle consisting of a circle having a smaller radius and a circle having a larger radius including the smaller circle has the same normal vector and a distance according to the above condition 2 two images of this concentric circle pattern are taken by one camera at different angles to obtain two sheets of image information a concentric circle projected at a given angle has a shape of an ellipse as shown in fig4 a to fig5 generally the central points of two ellipses do not match this is because two ellipses obtained by projecting concentric circles at different.