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Reverse Ray Tracing

Reverse ray tracing is one of the geometrical optics methods to simulate an optical system by tracing interactions of separate rays with the reflecting surface. The reverse ray propagation is plotted when a ray originates from the illuminated area and propagates toward the light and optical system until it crosses a light source. Reverse ray tracing is widely used in modern programs to calculate optical systems and lighting devices reflectors.

Reverse ray tracing in SHAPE is carried out according to the following algorithm:

  1. Description of the geometric and luminance properties of the light source luminous element;
  2. Description of the optical surface, including the normal vectors and reflecting matrix calculations;
  3. Parameterization and discretization of the optical surface;
  4. Receiving surface discretization;
  5. Description of a reverse ray;
  6. Calculation of a ray path after reflection (determination of an inner ray);
  7. Checking whether the ray intersects the light source;
  8. Calculation of the ray luminance value;

As a result, reverse ray tracing has its advantages:

  1. A smooth reflector shape is made possible without its approximation by linear segments;
  2. The computational complexity of the method depends only weakly on the optical-system complexity;
  3. High algorithmic parallelism of calculations (one can trace simultaneously and independently two or more rays and separate zones of illuminated area);
  4. Elimination of shaded areas.

Supporting reverse ray tracing and other approaches to reflector design, SHAPE is a powerful tool to create highly efficient optical systems.