# Component:Covering

## Covering Component

Covering (component COVR) is a modeling technique that fits a surface through one or more circuits of edges and builds the required topology for the resulting face or faces. A "circuit" of edges is a set of edges that are connected end-to-end and form a closed "loop". The term "circuit" is used to avoid confusion with the topological term "loop". The covering algorithm typically converts each circuit of edges into a loop on a face. Covering can be used to create sheet or open solid bodies from wire bodies, as well as add faces to existing sheet or solid bodies. The input edges can be specified using stand-alone edges (that is, edges with no upper topology), edges in sheet or solid bodies, or wire bodies.

Two distinct goals for covering are:

• Cover a wire body that has no associated face or surface information.
The pair of figures below demonstrates the covering of a wire. The four wire edges shown in Figure. A Wire Body Consisting of Four Edges are covered with a surface and the necessary topology is constructed to create the sheet body shown in Figure. A Sheet Body Consisting of a Single Face.
 Before Covering:A Wire Body Consisting of Four Edges After Covering:A Sheet Body Consisting of a Single Face
• Cover an opening in a sheet or solid body.
This is done by covering one or more circuits of free edges with a surface. When adjacent faces exist, it is not uncommon for the surface underlying one of them to be used to cover the opening. The pair of figures below illustrates how an existing surface can be utilized to cover an opening. The hole in the face shown in Figure. A Sheet Body Consisting of One Face with an L-shaped Hole is covered using the surface underlying the face. The resulting sheet body is shown in Figure. A Sheet Body Consisting of Two Faces Residing on the Same Surface.
 Before Covering: A Sheet Body Consisting of One Face with an L-shaped Hole After Covering: A Sheet Body Consisting of Two Faces Residing on the Same Surface
One variation of this is covering a circuit of edges in a solid body to create an internal face. The pair of figures below illustrates how an existing surface can be utilized to create an internal face.
 Before Covering: A Closed Solid Body After Covering: A Non-manifold Solid Body

Note: When covering a sheet body to create a solid, the sheet body should first be converted into a open solid body. This can be done with the function api_body_to_1d.

 Before Covering: A Two-sided Sheet Body After Covering: A Solid Body

## Covering Operations

The Covering Component provides the following functional variations of covering:

Operation Description
Basic Planar Covering
of Wires
Cover planar wires.
Enhanced Planar Covering
of Wires
Cover planar wires.
Enhanced Planar Covering
of Edges
Cover planar edges.
Non-Planar Covering
of a Single Wire
Cover a non-planar wire.
Non-Planar Covering
of Multiple Wires
Cover one or more non-planar wires.
Non-Planar Covering
of Free Edges
Cover one or more holes in a solid body.
Non-Planar Covering
of Edge Circuits
Cover one or more circuits of edges.

### Limitations in Covering Operations

Limitations in ACIS covering operations is available in Covering Limitations.

## Covering Topics

### Surface Generation

All of the covering API functions not restricted to generating planar surfaces use the same algorithm to generate a surface, if a surface is not specified. This surface generation algorithm makes multiple attempts to compute a surface. It attempts to generate the simplest analytic, B-spline, or procedural surface that will fit the boundary curves.

### Tolerant Entity Creation

All of the covering API functions not restricted to generating planar surfaces have a signature that accepts a cover_options object as an argument. A covering_options object allows a maximum gap tolerance to be specified. If a maximum gap tolerance greater than SPAresabs is specified, the API function may produce tolerant edges and vertices. For more information refer to Creation of Tolerant Entities.

It is possible that standard covering will not generate a suitable surface to cover the boundary edges. If this occurs, Advanced Covering is recommended.

## Covering Interface

### API Functions

Refer to Covering API Functions for a summary of the covering API functions. Library reference material for the covering API functions is also available.

### Scheme Extensions

Tables correlating the Scheme Extensions for covering with their corresponding API functions are presented in Covering Scheme Extensions. A complete listing of all covering related Scheme extensions is also available.

### Options

Some signatures of the covering API functions (including api_cover_sheet, api_cover_wires, api_cover_wire, and api_cover_circuits) take a cover_options object to control their behavior.

In addition, some global options affect the behavior of covering operations. Refer to covering global options.

### Error Codes

Upon the failure of a covering API function, a covering error code will be returned that explains the failure and suggests possible actions for correction.

### Journaling

Journaling is available for covering operations through the standard ACIS journaling mechanism.

### Versioning

Versioning is available for covering operations through the standard ACIS versioning mechanism.