Alternate Cell Descriptions

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Sometimes cell descriptions include one or more surfaces to avoid a very small overlaps other cells and prevent the cell from being recognized as a known shape. Such small overlaps are not a problem for the 3D display. In other cases, a cell description can be changed into a recognizable shape by eliminating redundant interior surfaces or decreasing the number of non-surface operators used.

To accommodate such changes, an alternate cell description can be defined. The alternate description is only used for the 3D display.

Alternate cell descriptions were used for the model shown here . The small intestine is the green wireframe box at the bottom. The original cell description

-91 +221 -222 +223 -7 ( +232 : +230 : -223 ) ( +240 : +241 : - 242 ) ( +232 : +250 : -223 )

excluded the enclosed portions of the large intestine by using explicit surfaces rather than complements. The alternate description

-91 +221 -222 +223 -7

specifies only the outer boundary of the cell.

The adrenals are the two purple cells at the upper right. The left and right adrenals carry separate transformations except for the bottom plane. An alternate description for one was used to introduce a plane with the same transformation as the other surfaces.

For all but the simplest cells, Moritz uses the extent of a cell’s 3D polygons to calculate the cell’s bounding box. If the alternate description results in 3D polygons that have a smaller extent than the actual cell, the bounding box will be incorrect, possibly affecting the 2D drawing of the cell and the ability to pick the cell in the 2D windows. Volume fraction calculations can also be affect. The BBox command is available to enter the correct bounding box. The command can also be used to prevent use of the 3D polygons in defining the cell’s bounding box.

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