Ray Termination
Use the Ray Termination feature to remove rays from the model as they exit the geometry, or to annihilate rays of sufficiently low intensity or power.
The Ray Termination feature can terminate rays at the exact time at which their intensity or power reaches the specified threshold, if there exists a closed-form analytic expression for this time. Such a closed-form analytic solution exists if:
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The rays represent planar wavefronts in an absorbing medium, or
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The rays represent spherical or ellipsoidal wavefronts in a non-absorbing medium.
Otherwise, the rays are stopped at the first time step for which the intensity or power is less than the threshold value.
Termination Criteria
If Compute intensity or Compute intensity in graded media is selected from the Intensity computation list in the physics interface Intensity Computation section, enter the Threshold intensity Ith (SI unit: W/m2). The default is 1e-3[W/m^2]. Rays with intensity lower than the threshold will be annihilated.
If Compute intensity and power or Compute intensity and power in graded media is selected from the Intensity computation list, it is possible to terminate rays based on the ray intensity or power, which are stored as separate degrees of freedom for each ray. Selection an option from the Termination Criteria list: Intensity (the default), Power, or Intensity and power. Based on this selection, enter the following:
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For Intensity or Intensity and power, enter the Threshold intensity Ith (SI unit: W/m2). The default is 1e-3[W/m^2].
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For Power or Intensity and power, enter the Threshold power Qth (SI unit: W). The default is 1e-3[W].
Regardless of whether the ray intensity is computed, select an option from the Spatial extents of ray propagation list: Bounding box, from geometry (the default), Bounding box, user defined, or None. This list controls whether rays are terminated based on their positions.
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For Bounding box, from geometry, a ray is immediately terminated if it reaches the surface of the bounding box of the geometry, defined as the smallest rectangle or rectangular prism with edges parallel to the axes of the global coordinate system that contains all of the geometric entities. This bounding box is extended by 5% in each direction so that rays can still interact with boundaries that coincide with the perimeter of the bounding box. Therefore rays can propagate a short distance away from the geometry before disappearing.
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For Bounding box, user defined, a ray is immediately terminated if it reaches the surface of a box of user-specified dimensions. To define the box, enter maximum and minimum values of each coordinate.
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For None, the rays that propagate outward from the geometry will continue to propagate until the study is complete. If the maximum path length for the Ray Tracing study step is too large, this may result in trajectories that are extremely long relative to the characteristic geometry size.
Ray Termination Theory