Defining the ray limits.
The ray limits define the values of the coordinates and the velocity components at which ray tracing will be stopped.
The coordinate limits can be used to stop rays before they enter uninteresting regions. The velocity limits are usually not important (and so are usually put as -1E10 to +1E10), but they can be used to stop reflected rays. Time limits are also available.
Another limit available in CPO3D is the distance 'rho' from the z axis (which is useful in lens studies) or the distance from the origin.
To let the program decide the ray limits, make at least one of the differences (that is, maximum-minimum) zero or negative (for example by making all the limits zero). The program will then use the already specified field of view to define the ray limits -that is, the program will stop a ray that goes outside the field of view (and will not allow a ray to start from a point outside the field of view).
Backward tracing, time markers