# Topology Module

Creates and accesses topological entities.

This module defines the following types of topological entities:

- Body: An exact 3D geometric representation of a solid, surfacic, or wireframe model. A topology body entity is contained in a representation item entity.

- Connex: For solids, a connex represents a continuous piece of material.

- Shell: A hollow sphere is represented by two shells (one inner and one outer).

- Face: Every shell is represented by a collection of faces sewn together. Each face holds an associated geometric surface.

- Loop: A face may be trimmed by several loops (one outer loop and multiple inner loops). Currently, HOOPS Exchange does not allow a face to have multiple outer loops. Instead, you can make several faces, each containing a single outer loop.

- Co-edge: A loop is a collection of oriented and ordered co-edges, containing space parametric curves (if any), and neighboring information. The current version of HOOPS Exchange handles only manifold solids which are solids that have single neighbors per co-edge.

- Edge: Each co-edge holds an edge, which in turn holds 3D information (if any), such as 3D curves and vertices.

  > An `A3DTopoContext`defines a global tolerance for every topological entity in this context. This global tolerance can then be superseded by less strict local tolerances for particular entities such as edges.

## Tolerance

In general, if the local tolerance is lower than the tolerance specified in the associated `A3DTopoContext`entity, you must use the tolerance from the `A3DTopoContext`entity.

> SingleWireBody, BrepData, Connex, Shell, Face, Loop, CoEdge, Edge, WireEdge

Topics

- Topology Body (the topology base entity)
- Topology Context
- SingleWireBody
- BrepData
- Connex
- Shell
- Face
- Loop
- CoEdge
- Edge
- WireEdge
- Vertex

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