(a) An excess brightness COR2-A image taken at 2011 March 7 20:24 (UT). The projection of the 3D shock front (green lines in panel (b)) on the image plane is shown with the dotted line. The diamond refers to the geometric center of the ellipsoid model projected onto the same plane. Two examples of radial cuts (relative to the geometric center), used to take the brightness profile, are shown by the two rectangles marked as Cut A and Cut B. Thick lines in the rectangles show the length of L used for the calculation of χ² (Fig. 4). (b) The excess brightness in panel (a) with the 3D shock front (green lines). The 3D geometry was modeled with the ellipsoid model in Kwon and Vourlidas (2017). (c) The geometric relation among the Sun, shell-like sheath, and LOS. A partial circle around the origin O is the solar disk. A shell-like sheath is represented in gray color. Arrows in black, blue and red are the LOS, the projected shock normal on the image plane, and the actual shock normal in 3D, respectively.