Maintaining tight precision yields the best modeling results, but is not always achievable. Tolerant modeling in
ACIS increases the scope of the data that
ACIS can import. It solves the problems associated with importing inaccurate data or "leaky" models and provides the framework for model healing and data translation.


Tolerant modeling accepts less precise geometric data and creates valid topology. The software attaches tolerance values to edges and vertexes, so that even when edges do not intersect within
SPAresabs, they're brought close enough to be useful.


Tolerant modeling can also be used to handle approximations for operations that don't require as much precision. Because speed is inversely proportional to precision,
ACIS offers users a choice: precision at the cost of speed, or speed at the cost of precision when approximations can suffice. While blending provides support for tolerant or neartangent models, blending will continue to work best with precise data and, where possible, exact tangencies.


Tolerant modeling does not impact the robustness and reliability of the exact modeling in
ACIS. The constructs needed for tolerant modeling are derived from the
EDGE,
COEDGE, and
VERTEX topology classes. Deriving from the base topology elements minimizes the impact to other areas of
ACIS. The geometry that describes these tolerant elements and their intersections is same geometry used by the standard elements.


Tolerances are maintained by the system and are updated after each operation with no user input necessary. Users may query the tolerance values, but not set them. The range of testing of tolerant models has been a maximum of about 10 percent of the model size. For example, a block with a height 100, width 100, and depth of 100 has been tested with a tolerant edge with a tolerance of 10.


In the online help, refer also to these related subjects:



Healing


Precision and tolerance


Model topology
