Model Topology
Topology refers to the spatial relationships between the various entities in a model. Topology describes how geometric entities are connected (connectivity). On its own, topology defines a "rubber" model, whose position is not fixed in space. For example, a circular edge and an elliptical edge are topologically equivalent (but not geometrically). Likewise, a square face and a rhomboid face are topologically equivalent (but not geometrically). A topological entity's position is fixed in space when it is associated with a geometric entity.
Topology can be bounded, unbounded, or semi-bounded, allowing for complete and incomplete bodies. A solid, for example, can have missing faces, and existing faces can have missing edges. Solids can have internal faces that divide the solid into cells. Bodies such as these are not physically realizable, but can be represented with ACIS.
ACIS separately represents the geometry (detailed shape) and the topology (connectivity) of objects. This concept is called boundary representation, or B-rep, modeling. This provides the ability to determine whether a position is inside, outside, or on the boundary of a volume (which distinguishes a solid modeler from surface or wireframe modelers). ACIS defines the boundary between solid material and empty space. This boundary is made from a closed set of surfaces.
Topics include:
- Topology and Boundary Representation
- Bodies
- Lumps
- Shells
- Subshells
- Faces
- Loops
- Wires
- Coedges
- Edges
- Vertices
- Tolerant Modeling
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