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Cutter bodies are used in conjunction with ray tracing to view the interior of the object without making the exterior completely transparent or semi-transparent. The cutter body, which can be any of the primitive bodies available in Sabrina, permits sections to be cut out of the geometry model. Some of the interior of a model can be seen while still displaying the exterior.
No surfaces of the cutter body may be cell boundaries. This restriction also means that, in MCNP mode, no surface of the cutter body should coincide with an MCNP surface. If such a coincidence exists, Sabrina will not accept the body as a cutter body.
In computing COLOR or ETCH pictures, Sabrina traces rays from the viewpoint to the geometry model. If one or more cutter bodies have been defined, the algorithm checks to see if the current ray intersects a cutter body. If so, the ray is tracked until it exits the cutter body and then tracked to the geometry in the normal manner. Some opaque geometry may be encountered immediately on exiting from the cutter body. Any portions of the geometry, either inside or in front of the cutter body, are "cut out'' of the image. Opaque bodies in front of the cutter body will not be visible. The cutter bodies have no effect on the geometry model.
Up to 50 cutter bodies may be defined. The ability to define and use cutter bodies works on both body geometry models and on MCNP surface geometry models. The cutter body feature works only with the COLOR and the ETCH command, not with DRAW or RDRAW.
When a user defines multiple cutter bodies, Sabrina proceeds to check all bodies in the order the user has referenced them. This can be confusing if one cutter body is in front of a second. The front cutter body will take priority over the cutter body behind it if it occurs first in the user input list. Using multiple cutter bodies is more useful if the cutter bodies do not overlap; many independent sections of a geometry may then be exposed with different cutter bodies.
If a window is not defined for body geometry, Sabrina first computes a line drawing in order to determine the scaling. The scaling is based on all bodies present, including those which are used as cutter bodies. The presence of a cutter body much larger than the real model can set the scaling so that the geometry is too small to be visible.
Cutter Bodies and Particle Tracks
The Cutter Bodies submenu of the Graphics menu controls their use. Cutter bodies are also controlled with the ICUT command.
Right parallelepipeds (RPPs) are useful as cutter bodies when a half space or quadrant is to be removed. For example,
RPP 44 0 5000 0 5000 -5000 5000; ICUT 44
cuts out the entire positive X and positive Y quadrants (assuming the model does not extend past 5000 in any direction). The define RPP... button on the Cutter Body dialog shows a dialog for defining an RPP (or modifying an existing one).