In Euclidean geometry, a figure formed by a point on a straight line and the part next to it is called a ray or a semi-straight line. In geometrical optics, light is a curve describing the propagation direction of light or other electromagnetic radiation. This ray is perpendicular to the wavefront of physical optics. In most simple cases, the light in a given conductor is a straight line. When it passes through one conductor to another, it will be refracted or totally internally reflected according to Snell's law. The characteristic (1) ray has only one endpoint, and it extends from one endpoint to the other indefinitely. (2) Ray is unpredictable. Parameter equation p = p0+tu, where p0 is the starting point of the ray, u is the direction of the ray, and the range of t is.