Method for obtaining the optical projection mechanism of a camera
The present invention provides a method for obtaining the optical projection mechanism of a camera, particularly one equipped with a fisheye lens. The method first establishes the camera's optical axis and projection center. A stereoscopic target having a patterned front surface and at least one patterned side surface is placed so that the projection center aligns with the target center and the optical axis is normal to the front surface. Images of the target captured by the camera form a second pattern on the image plane. By correlating the known first pattern on the target with the second pattern on the image plane, viewing lines across the full field of view—including off-axis angles exceeding 90°—are derived, yielding an accurate mapping between image coordinates and real-world directions. The resulting projection model enables precise distortion correction and dimensional measurement across the camera's wide field of view.
1 . A method for obtaining a camera's optical projection mechanism, the camera including a lens and being configured to project an image of a physical object in a field-of-view space onto an image plane, the image formed by the camera having axisymmetric and nonlinear distortion properties, the method comprising:
(a) confirming an optical axis of the camera and a projection center of the camera;
(b) providing a stereoscopic target including a front view surface and at least one side view surface, wherein both the front view surface and the at least one side view surface have a first pattern;
(c) forming an image of the first pattern on the front view surface and the side view surface onto the image plane to create a second pattern;
(d) aligning the projection center of the camera with a center point of the front view surface of the stereoscopic target, and making the optical axis perpendicular to the front view surface; and
(e) comparing the first pattern with the second pattern to find a corresponding relationship between the first pattern and the second pattern, thereby obtaining the optical projection mechanism of the camera.
2 . The method of claim 1 , wherein the first pattern is composed of a plurality of regularly arranged shapes.
3 . The method of claim 1 , wherein the first pattern covers the front view surface or the side view surface.
4 . The method of claim 2 , wherein the first pattern has a first color and a second color, each of the shapes has a color that is the first color or the second color, and the shapes of the first color and the shapes of the second color are arranged alternately.
5 . The method of claim 4 , wherein the first color is black and the second color is white.
6 . The method of claim 5 , wherein the shapes are squares.
7 . The method of claim 2 , wherein the stereoscopic target is a cubic box having an opening, an interior of the cubic box including the front view surface and four side view surfaces, and the opening exposing the front view surface and the side view surfaces.
8 . The method of claim 1 , wherein the lens is a fisheye lens.