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Topology
The core LOP capability is to be able to intersect unbounded surfaces and curves to create ACIS edges and vertex topology. Two types of intersections are used to support this:
- Intersection of two unbounded surfaces to get a single curve.
- Intersection of an unbounded edge with an unbounded surface to get a single point. In some cases curve-curve intersections are preferred, but not typically.
LOP expects to see edges and vertices from the intersections at all times. If more than one edge or vertex position is possible, LOP will test each to determine which is best. It fails whenever this condition is violated, as when the unbounded surfaces (or unbounded curves) never intersect (for example, two parallel planes).
For example, the operation for moving faces requires that the underlying curves be recomputed for the edges of each face being moved, as well as the face's vertex coordinates. If the top face of a cube is moved, each of the four top edges' curves are recomputed by intersecting the moved top plane with the four side planes. The four vertices are recomputed by either intersecting the four side straights with the top face plane or by intersecting the new four top straights with the side planes. This new geometry is then copied to the old edge and vertex topology of the moved face. If the new geometry for a moved face and its edges interferes with any other part of the block, no check is performed and a self-intersecting body is the result, unless the option lop_repair_self_int is TRUE, in which case the problem will be fixed in the Repair Body Intersections Component.
The other local operations are quite similar. The operation for offsetting a body copies and offsets all of the surfaces in the body. Then, based on the old body's coedges, it intersects each offset with its neighbors to get new curves. The tweak operation simply replaces a surface instead of moving one.
LOP multiple solutions algorithm handles the general multiple solution problem. Points are calculated by intersecting the corresponding curve and surface. Curves are calculated by intersecting corresponding surfaces. Intersections that do not preserve the original topology are eliminated with the default settings. Any solutions that do not maintain the original convexity are also eliminated. Of the remaining solutions, one is chosen using a distance criteria that varies depending on the particular operation. The way this algorithm works will change depending on the setting for various options, including lop_repair_self_int. This, together with the curve and surface extension capability, enables the solution of local operation problems not involving unsupported changes in topology.
Related topics:
Types of Local Operations
Adaptive Offset
Body Repair
Blended Faces
Remove Faces
Defeaturing
Limitations[Top]
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