Local Operations
List of: Discussion Topic
Subjects: Tolerant Modeling
Contents: Kernel

All local operations, including tweak, move, taper, shell, offset, and sweep-more, are tolerant modeling friendly. This means that local operations behave sensibly when tolerant geometry is encountered. (The tweak algorithm is the foundation for all other local operations.)

When non-tolerant edge geometry does not lie on adjacent faces to within SPAresabs (indicating a failure earlier in the operation), the edge can be made tolerant to allow the operation to finish. In these cases a tolerant edge is only created when the tolerance will be less than 100.0 * SPAresabs.

When an edge tangent to ACIS tolerance whose geometry is not a line is found between a plane and a cone, the edge is made tolerant and a straight is substituted for the edge geometry. (Mathematically it is easy to prove tangent intersection curves between planes and cones must be lines. Using this fact, local operations is able to simplify model geometry and speed the operation.) Imported data shows this problem where planes and cones do not quite line up.

Non-tangent tolerant edges (or tolerant edges that become non-tangent or non-near tangent in the local operation) are reverted to ordinary edges by using the precise geometry from the intersection of the edge's adjacent surfaces, as shown in Figures 6-2 and 6-3.

Figure 6-2. Before face is moved

Figure 6-3. Lateral tolerant edge reverted to ordinary geometry

When a vertex position cannot be determined, the vertex is made tolerant and the operation is repeated before the local operation is allowed to fail.