The Subtract mode allows to remove parts of the original structure by subtracting a structure from it.

Voxel Geometry

If the Geometry Mode Voxel Geometry is chosen, the structures are subtracted based on the voxel information alone. If analytic data was present in the geometry files before, this data is discarded.

For example, a cylinder is used to remove a portion of the glass fibers, leaving a circular hole in the center of the resulting structure. As seen for the Attach and the Add modes, the combined structure uses the constituent material information of the original structure. With the default setting (Subtract Bit-Wise unchecked), the subtraction process sets all material overlap between the two structures to Material ID 00.

Or in another case, a cylindrical hole (made by inverting the previous cylinder with ProcessGeo – Invert) is used to obtain a cylindrical portion at the center of the glass fibers structure.

Subtract Bit-Wise

When Subtract Bit-Wise is checked, the Material IDs of the overlapping structure parts are determined by bit-wise subtracting the Material IDs.

For example, if we reassign the Material ID 01 to Material ID 03 in the GlassFibers.gdt structure (with ProcessGeo - Reassign Material ID) and subtract an object with Material ID 01 (Cylinder.gdt) with Subtract Bit-Wise, it does not produce the combined structure with the hole (since 0011-0001=0010).

Analytic Geometry

If Analytic Geometry (gad) is chosen as Geometry Mode, the analytic objects are subtracted. Subtract Bit-Wise is not available, instead any overlap is set to Material ID 00. This works only when both structures (the chosen file and the current structure) have analytic information. The result is the same compared to the voxel method without subtracting bit-wise but the analytic information is preserved.

Offsets

As described, by setting Offsets different from 0, the structure can be subtracted at any location. For example, the cylinder from the first example is subtracted with an offset of 50 voxels in X direction and a Y offset of 50 voxels, such that the removal of glass fibers is not in the center and the hole appears closer to the corner.