2.4 Face Commands

The following commands are available on the Geometry/Face subpad.

2.4.1 Form Face

The Form Face command button allows you to perform the following operations.

The following sections describe the purpose and operation of each of the Face commands listed above.

Create Face From Wireframe

The Create Face From Wireframe command allows you to create a face from three or more existing edges.

To create a face by means of the Create Face From Wireframe option, you must specify the following parameters:

• The edges that define the wireframe
• The face type—real or virtual

Specifying Edges of the Wireframe

GAMBIT employs the following rules for specifying edges used to create a face by means of the Create Face From Wireframe option.

• The sequence in which you specify the wireframe edges does not affect the final form of the face.
• The edges do not have to be connected to each other, but each edge must possess endpoint vertices that are coincident with the endpoint vertex of one other specified edge (see Figure 2-53).

Figure 2-53: Wireframe endpoint vertex requirements

Specifying the Face Type

GAMBIT allows you to create both real and virtual faces using the Create Face From Wireframe command. To create a real face, you must specify only real edges for the wireframe. To create a virtual face, you can specify any combination of real and/or virtual edges for the wireframe.

Creating a Real Face

The following rules apply to the creation of a real face.

• To construct a real face, you must specify only real edges for the wireframe.
• If the specified edges are not coplanar, GAMBIT applies the following rules with respect to the creation of the face.
• If you specify only two edges, GAMBIT attempts to construct a skin-surface face. (See "Create Real Skin Surface Face," below.)
• If you specify three or four edges, GAMBIT checks the orientation of the edges to determine whether the edges meet with tangent continuity at their endpoints. If the edges don't meet with tangent continuity, GAMBIT does not create the face.

Creating a Virtual Face

If you specify the creation of a virtual face, you can also specify a host face or volume.

• If you do not specify a host face or volume, GAMBIT creates an orphan face—the shape of which is defined only by means of its boundary edges.
• If you specify a host face or volume, GAMBIT creates a parasite face and employs the existing geometry (shape) of the host entity to define the shape of the virtual face.

Specifying the Tolerance Value

If you specify a host face for the creation of a virtual face, GAMBIT allows you to specify a Tolerance value. The tolerance value consitutes the maximum allowable distance between the wireframe edges and the surface of the host face.

Using the Create Face From Wireframe Form

To open the Create Face From Wireframe form (see below), click the Create Face From Wireframe command button on the Geometry/Face subpad.

The Create Face From Wireframe form includes the following specifications.

Create Real Parallelogram Face

The Create Real Parallelogram Face command allows you to create a real, four-sided face in the shape of a parallelogram.

To create a face by means of the Create Real Parallelogram Face option, you must specify three existing real vertices that define the face. The vertices are designated as Origin, Base, and Inclineand are defined as shown in Figure 2-54.

Figure 2-54: Parallelogram—face vertex definitions

The edges formed in the creation of the face are defined such that their senses are from the Origin vertex to the Base vertex and from the Incline vertex to the Origin vertex. If you reverse the specifications regarding which vertices constitute the Base and Incline vertices, respectively, the shape of the resulting face does not change, but GAMBIT reverses the sense of each of its edges.

Using the Create Real Parallelogram Face Form

To open the Create Real Parallelogram Face form (see below), click the Create Real Parallelogram Face command button on the Geometry/Face subpad.

The Create Real Parallelogram Face form includes the following specifications.

The Create Real Polygon Face command allows you to create a planar, polygonal face defined by a set of existing real vertices. (NOTE: If you specify a set of five or more vertices, all vertices in the set must be coplanar.)

To execute the Create Real Polygon Face command, you must specify a set of at least three vertices. To create the polygonal face, GAMBIT first creates a closed loop of edges that join the specified vertices then creates a face bounded by the closed loop.

The order in which the vertices are specified on the Create Real Polygon Face form determines the order in which the bounding edges are created— which, in turn, affects the shape of the created face. As an example of this effect, consider the set of six vertices shown in Figure 2-55(a).

Figure 2-55: Effect of vertex specification sequence

Figure 2-55(b) and Figure 2-55(c) show two example faces created using the vertex specification sequences listed in the following table.

To open the Create Real Polygon Face form (see below), click the Create Real Polygon Face command button on the Geometry/ Face subpad.

The Create Real Polygon Face form includes the following specifications.

The Create Real Circular Face From Vertices command allows you to create a planar face in the shape of a full circle.

GAMBIT provides two methods for creating a face in the shape of a full circle. Both methods require you to specify three existing vertices to define the size and location of the circle. The methods are defined as follows:

• Method 1—specifies one vertex that constitutes the center of the circle and two vertices that lie on the circular edge that bounds the face
• Method 2—specifies three vertices that lie on the circular edge that bounds the face

Method 1 (Figure 2-56(a)) requires that the two vertices that lie on the circular bounding edge are equidistant from the vertex at the center of the circle. Method 2 (Figure 2-56(b)) requires only that the three specified vertices are not collinear.

Figure 2-56: Circular face specifications

To open the Create Real Circular Face From Vertices form (see below), click the Create Real Circular Face From Vertices command button on the Geometry/ Face subpad.

The Create Real Circular Face From Vertices form includes the following specifications.

The center section of the Create Real Circular Face From Vertices form varies according to the method selected to construct the bounding circle. The specifications available on the center section of the form are as follows.

When you specify Method 2 for the creation of a circular face, the middle section of the Create Real Circular Face From Vertices form appears as shown below.

The Create Real Elliptical Face From Vertices command allows you to create a face that represents a section of a full ellipse.

To create an elliptical face, you must specify the following parameters (see Figure 2-57):

• Center vertex—located at the center of the full ellipse
• Major vertex—defines the length of the major axis
• On Edge vertex—defines the dimensions of the full ellipse
• Start Angle and Stop Angle— define the size and location of the elliptical section that bounds the face

Figure 2-57: Elliptical face specifications

The Center, Major, and On Edge vertices define the shape and size of the full ellipse of which the face constitutes a section. The Start Angle and Stop Angle define the size and position of the face relative to the Center vertex and major axis. (NOTE: The three vertices that define the ellipse must not be collinear.)

To open the Create Real Elliptical Face From Vertices form (see below), click the Create Real Elliptical Face From Vertices command button on the Geometry/ Face subpad.

The Create Real Elliptical Face From Vertices form includes the following specifications.

Create Real Skin Surface Face

The Create Real Skin Surface Face command allows you to create a real, four-sided face by specifying a series of edges that define its surface.

Specifying Edges for a Skin-Surface Face

To create a face by means of the Create Real Skin Surface Face option, you must specify two or more existing edges that define the face. The first and last edges that you specify comprise two of the four sides of the face. The other two sides consist of continuous curves fit through the start and end endpoint vertices of all specified edges. The surface of the created face constitutes an interpolation through all of the edges specified for the face.

As an example of edge specification for the Create Real Skin Surface Face operation, consider the four edges shown in Figure 2-58(a). If you use all four edges to create a face by means of the Create Real Skin Surface Face operation, GAMBIT creates a face such as that shown in Figure 2-58(b).

Figure 2-58: Create Skin Surface Face edge specifications

The first and last edges specified (1 and 4, respectively) comprise two of the four boundary edges of the skin-surface face. The other two boundary edges (5 and 6) consist of continuous curves constructed through the endpoint vertices of the original four edges.

NOTE (1): The order in which you specify edges determines the shape of the resulting face. For example, to create the face shown in Figure 2-58(b), you must specify the edges in the order (1, 2, 3, 4) or (4, 3, 2, 1), rather than (1, 4, 2, 3) or (3, 2, 1, 4).

NOTE (2): GAMBIT ignores edge sense when creating a face by means of the Create Skin Surface Face operation. For example, the final shape of the face shown in Figure 2-58(b) is independent of the senses of the edges that define its surface.

Using the Create Real Skin Surface Face Form

To open the Create Real Skin Surface Face form (see below), click the Create Real Skin Surface Face command button on the Geometry/Face subpad.

The Create Real Skin Surface Face form includes the following specifications.

Create Real Net Surface Face

The Create Real Net Surface Face command allows you to create a real, four-sided face by specifying two sets of logically parallel edges that define the boundaries and shape of its surface.

Specifying Edges for a Net-Surface Face

To create a face by means of the Create Real Net Surface Face option, you must specify two or more sets of existing edges that define the shape of the face. Each set must include at least two edges. The surface of the created face constitutes an interpolation through all of the edges specified for the face.

As an example of edge specification for the Create Real Net Surface Face operation, consider the edges shown in Figure 2-59(a). The figure consists of nine edges, four of which (designated by the letter u) are logically perpendicular to the other five (designated by the letter v).

Figure 2-59: Create Net Surface Face edge specifications

If you use all four edges in the u direction and all five edges in the v direction to create a net-surface face, GAMBIT creates a face such as that shown in Figure 2-59(b). If you specify edges in either direction the lengths of which exceed the boundary defined by the first or last edges specified in the other direction, GAMBIT truncates the created face. As an example of such truncation, consider the edges shown in Figure 2-59(a), above. If you specify edges 2, 3, and 4 in the u direction and edges 2, 3, 4, and 5 in the v direction, GAMBIT creates the net-surface face shown in Figure 2-59(c). Note that the final form of the net-surface face approximates the intersection of skin-surface faces created by means of edges 2, 3, and 4 in the u direction and edges 2, 3, 4, and 5 in the v direction.

NOTE (1): To create a face by means of the Create Net Surface Face operation, you must specify the edges monotonically in each direction with respect to their relative positions in defining the face. For example, to create the face shown in Figure 2-59(b), you must specify the u-direction edges in the order (1, 2, 3, 4) or (4, 3, 2, 1) and the v-direction edges in the order (1, 2, 3, 4, 5) or (5, 4, 3, 2, 1).

NOTE (2): GAMBIT ignores edge sense when creating a face by means of the Create Net Surface Face operation. For example, the final shape of the face shown in Figure 2-59(b) is independent of the senses of the edges that define its surface.

Specifying the Tolerance Option

If the edges in the u direction do not exactly intersect the edges in the v direction (or vice versa), you must select the Tolerance option and specify a tolerance value. The tolerance value is the maximum allowable distance between any of the edges and the resulting face.

Using the Create Real Net Surface Face Form

To open the Create Real Net Surface Face form (see below), click the Create Real Net Surface Face command button on the Geometry/Face subpad.

The Create Real Net Surface Face form includes the following specifications.

Create Real Face From Vertex Rows

The Create Real Face From Vertex Rows command allows you to create a four-sided face by specifying a series of vertex rows that define the surface of the face.

To create a face by means of the Create Real Face From Vertex Rows option, you must specify the following parameters:

• A sequence of vertices that define the face
• The number of rows of vertices to be used in defining the face
• The method used to fit curves through the vertices that define the face

The vertex locations define the overall shape of the face. The number of rows determines the shape and numbering of the edges created in the creation of the face.

Specifying the Vertex Sequence

When you specify vertices for the Create Real Face From Vertex Rows operation, you must select the vertices in an ordered sequence that represents the position of each vertex in a sequential series of rows. That is, you must specify all the vertices that constitute the first row, then all the vertices that constitute the second row, and so on.

The first and last rows of vertices specified define edges that comprise two of the four sides of the face. The other two sides of the face consist of continuous curves fit through two sets of vertices defined as follows:

• The first vertex specified in each row
• The last vertex specified in each row

As an example of vertex specification for the Create Real Face From Vertex Rows operation, consider the face shown in Figure 2-60. The face is defined by four rows of three vertices each. The numbers associated with the vertices in the figure indicate the sequence in which the vertices are specified when creating the face.

Figure 2-60: Create Real Face From Vertex Rows specifications—4 rows

Specifying the Number of Vertex Rows

When you create a face by means of the Create Real Face From Vertex Rows operation, you must specify the number of rows represented by the specified vertices. The total number of vertices must represent an integer multiple of the number of vertex rows. For example, if you specify a total of 12 vertices, you must specify either 2, 3, 4, or 6 vertex rows. The number of vertices in each row is equal to the total number of vertices divided by the number of rows.

It is possible to create a face of a given shape using two different specifications for the number of rows. For example, the face shown in Figure 2-61 represents a face created from the same set of vertices employed to create the face in Figure 2-60. The face differs from the face in Figure 2-60 in that it is created by specifying three rows of four vertices each rather than four rows of three vertices each.

Figure 2-61: Create Real Face From Vertex Rows specifications—3 rows

Although the shapes of the two faces are identical to each other, they differ in two respects:

• The sequence in which the vertices are specified
• The numbering of the edges created in the creation of the face

Specifying the Curve Fit Method

GAMBIT allows you to specify one of two methods by which curves are fit through the vertex rows to define the face. The two methods are as follows.

• Interpolate
• Approximate

If you select the Approximate method, you must also specify a Tolerance value. (For a description of the Interpolate and Approximate methods and the Tolerance value, see "Specifying the Curve Construction Method" in Section 2.3.1, above.)

Using the Create Real Face From Vertex Rows Form

To open the Create Real Face From Vertex Rows form (see below), click the Create Real Face From Vertex Rows command button on the Geometry/ Face subpad.

The Create Real Face From Vertex Rows form includes the following specifications.

Revolve Edges

The Revolve Edges command allows you to create real, two-, three-, or four-sided faces by revolving existing edges about a specified axis.

To create a face by means of the Revolve Edges option, you must specify the following parameters:

• One or more real or non-real edges to be revolved
• The axis of rotation
• The angle through which the edges are revolved about the axis

When you create a face by revolving an edge, GAMBIT sweeps the edge through the specified angle of rotation (see Figure 2-62). One of the edges that GAMBIT creates in the process of creating the face is a duplicate of the edge to be revolved. The other two edges are circular arc edges centered at the axis of rotation. If the axis of rotation passes through either endpoint of an edge to be swept, GAMBIT does not execute the Revolve Edges operation.

Figure 2-62: Revolve Edge operation

Specifying Edges to Be Revolved

To create faces by means of the Revolve Edges form, you must specify one or more real or non-real edges to be revolved about the axis of rotation. GAMBIT creates a separate face corresponding to each specified edge. The specified edges can be straight or curved, and they do not have to be coplanar with the axis of rotation.

NOTE: If you revolve a non-real edge to create a face, GAMBIT first creates a real copy of the non-real edge, then revolves the real copy to create the face.

Specifying the Axis and Angle of Rotation

To specify the axis of rotation, you must define the axis by means of the Vector Definition form. For a description of the Vector Definition form and its operation, see "Using the Vector Definition Form" in Section 2.1.4. The conventions regarding the angle of rotation for the Revolve Edges operation are identical to those described in "Rotating an Entity" in Section 2.1.4.

Using the Revolve Edges Form

To open the Revolve Edges form (see below), click the Revolve Edges command button on the Geometry/Face subpad.

The Revolve Edges form includes the following specifications.

Sweep Edges

The Sweep Edges command creates real faces by sweeping one or more edges along a specified path. If you sweep a non-real edge to create a face, GAMBIT first creates a real copy of the non-real edge, then sweeps the real copy to create the face.

To create a face by means of the Sweep Edges command , you must spec­ify the following parameters.

• Profile
• Path
• Type

Specifying the Sweep Profile

Specifying the Sweep Path

• Edge
• Vector

When you define the sweep path by specifying a vector, GAMBIT defines the path as a straight line possessing the magnitude and direction of the vector. You must define the vector by means of the Vector Definition form (see "Using the Vector Definition Form" in Section 2.1.4).

Specifying the Sweep Type

GAMBIT provides two general types of sweep operations:

• Rigid
• Perpendicular

Performing a Rigid Sweep

When you perform a rigid sweep operation, GAMBIT projects the profile along the entire length of the specified path without altering the orienta­tion of the profile. The shape and orientation of a face created by means of a rigid sweep operation depend on two factors:

• The shape of the profile and its orientation relative to the path
• The shape and direction of the path

The following examples demonstrate the effects of the shapes and orienta­tions of the profile and path on the final form of a face created by means of a simple rigid sweep operation.

Rigid Sweep—Profile Perpendicular to the Path

Figure 2-63 illustrates a rigid sweep operation in which the path and profile consist of straight edges oriented perpendicular to each other. In this case, the profile is aligned with the x coordinate axis, and the path lies in the y-z coordinate plane.

Figure 2-63: Rigid sweep—straight, perpendicular profile and path

To create a face by means of the rigid sweep operation, GAMBIT performs the following two-step procedure (see Figure 2-63(b)):

1. Project copies of the path onto the profile endpoints.
2. Project a copy of the profile, itself, to connect the upper endpoints of the projected paths.

Rigid Sweep—Profile Not Perpendicular to the Path

The profile edges for a rigid sweep operation can be located anywhere in the model domain as long as they are not parallel to the path. For example, Figure 2-64 shows a rigid sweep operation similar to that shown in Figure 2-63 but in which the profile consists of a curved, circular arc edge that lies in the x-z plane. As in the previous example, the boundary edges of the created face consist of the original profile edge, a projected copy of the profile edge, and two edges that represent projected copies of the path.

Figure 2-64: Rigid sweep—profile not perpendicular to the path

Rigid Sweep—Curved Path

The path used for a rigid sweep opera­tion can be straight or curved. To employ a straight path, you can define the path by means of either a straight edge or a vector. To employ a curved path, you must define the path by means of a curved edge.

Figure 2-65 shows a rigid sweep operation similar to that shown in Figure 2-64 but for which the path consists of a circular arc edge that lies in the y-z plane. As in the two previous examples, the boundary edges of the created face consist of the original profile edge, a projected copy of the profile edge, and two edges that represent projected copies of the path.

Figure 2-65: Rigid sweep—curved profile, curved path

Performing a Perpendicular Sweep

 Overview

Perpendicular sweep operations differ from rigid sweep opera­tions in that, for perpendicular sweeps, the initial orientation between the profile and path is main­tained along the entire length of the sweep path. Rigid sweeps, by contrast, maintain the orientation of the profile with respect to the global coordinate system along the sweep path.

As an example of the difference between rigid and perpendicular sweep operations, consider the profile and path shown in Figure 2-66(a). In this case, the profile consists of a straight edge aligned with the y coordinate axis, and the path is defined by a circular arc edge that lies in the y-z plane.

Figure 2-66: Example Rigid and Perpendicular sweep operations—curved path

The differences between the created faces can be summarized as follows.

• If you perform a rigid sweep using the path and profile shown in Figure 2-66(a), GAMBIT maintains the angle of the profile with respect to the global coordinate system, thereby creating the horn-shaped face shown in Figure 2-66(b).
• If you perform a perpendicular sweep with a zero draft angle (see below), GAMBIT maintains the angle between the path and profile and creates the face shown in Figure 2-66(c).

Perpendicular sweep operations can be modified such that the boundary edges of the created face deviate from the projected sweep path by a specified angle. Such modifications are specified by means of the following options on the Sweep Edges form:

• Draft
• Twist

Draft Option

To sweep a single profile edge-such as that shown in Figure 2-66, above-by means of the perpendicular draft operation, GAMBIT performs the following procedure (see Figure 2-67):

1. Project a copy of the path onto the start endpoint of the profile edge (Figure 2-67(a)).
2. Trace the end endpoint of the profile edge along the projected path, maintaining the original angle between the profile and projected path (Figure 2-67(b)).
3. Project a copy of the profile, itself, to connect the endpoints of the projected profile and traced end endpoint (Figure 2-67(c)).

NOTE: The procedure described above applies strictly only to sweep operations that involve a zero draft angle. For a description of the effect of draft angle on faces resulting from perpendicular draft sweep operations, see "Effect of Draft Angle," below.

Figure 2-67: Perpendicular draft method—procedure

The characteristics of the face created from a perpendicular draft sweep operation depend, in part, on the following factors:

• Profile edge sense
• Draft angle

Effect of Profile Edge Sense

As noted above, when you sweep an edge by means of the perpendicular draft method and specify a zero draft angle, GAMBIT copies and projects the profile onto the start endpoint of the profile edge and maintains the angle between the profile and path along the entire length of the path. Consequently, the start and end endpoint designations (which determine the edge sense) influence the shape of the created face.

As an example of the dependence on edge sense described above, consider the path and profile shown in Figure 2-68(a). The path consists of a circular arc edge that lies in the y-z plane, and the profile consists of a single edge aligned with the y coordinate axis.

Figure 2-68: Effect of profile sense on swept face

The characteristics of the face created by means of a perpendicular draft sweep of the profile shown in Figure 2-68(a) depend on the sense of the profile edge in the following manner.

• If the profile edge is defined such that vertex A constitutes its start endpoint, the sweep operation results in the face shown in Figure 2-68(b). To create the face shown in Figure 2-68(b), GAMBIT copies the path edge and projects it onto vertex A of the initial profile. In this case, the outer curved boundary edge of the face represents the copied projection of the sweep path.
• If the profile edge is defined such that vertex B constitutes its start endpoint, the sweep operation results in the face shown in Figure 2-68(c). To create the face shown in Figure 2-68(c), GAMBIT copies the path edge and projects it onto vertex B of the initial profile. In this case, the inner curved boundary edge of the face represents the copied projection of the sweep path.

Effect of Draft Angle

When you perform a sweep operation by means of the draft method, GAMBIT allows you to specify a draft angle for the created face. The draft angle specifies the angle by which the boundary edges of the created face deviate from the projected path.

The effect of the draft angle specification depends strongly on the shapes and orientations of the profile and path relative to each other. Figure 2-69 shows the effect of draft angle for two simple profiles and paths similar to those shown above.

Figure 2-69: Effect of draft angle on swept face

In Figure 2-69(a), the path and profile consist, respectively, of a circular arc edge aligned with the y-z plane and a straight edge aligned with the y coordinate axis. In this case, the draft angle determines the angle by which the plane that contains the created face deviates from the y-z plane.

NOTE (1): For the path and profile configuration shown in Figure 2-69(a), the perpendicular draft sweep operation always creates a planar face aligned with the y coordinate axis, regardless of draft angle. NOTE (2): The projections of the three faces shown in Figure 2-69(a) onto the y-z coordinate plane are identical to each other in shape, size, and orientation.

In Figure 2-69(b), the path consists of a circular arc edge aligned with the y-z plane the profile edge is aligned with the x coordinate axis. In this case, the draft angle specification serves to increase or decrease the size of the swept arc represented by the created face.

Twist Option

When you perform a perpendicular sweep operation by means of the twist option, GAMBIT revolves the profile through a specified angle as it sweeps the profile along the length of the path. The profile and path can be either straight or curved, but curved paths require an additional restriction with respect to the orientation between the profile and path (see below).

Using a Straight Path

Figure 2-70 illustrates the effect of the perpendicular twist sweep operation for a configuration that involves a straight sweep path. In this case, the profile is defined by a circular arc edge that lies in the x-z plane, the path is defined by a straight edge that is similar in orientation to that shown in Figure 2-63, above, and the twist angle is specified as 360^o.

Figure 2-70: Effect of perpendicular twist sweep operation—straight path

Using a Curved Path

Under certain circumstances, GAMBIT allows you to perform twist sweep operations using a curved path. Figure 2-71 illustrates the effect of the twist sweep operation for a configuration that involves a curved path. In this case, the path is defined by a circular arc edge similar in orientation to that shown in Figure 2-65. The profile consists of a single, straight edge one endpoint of which is connected to the start point of the path, and the twist angle is specified as 180^o.

Figure 2-71: Effect of perpendicular twist sweep operation—curved path

Using the Sweep Edges Form

To open the Sweep Edges form (see below), click the Sweep Edges command button on the Geometry/Face subpad.

The Sweep Edges form includes the following specifications.

2.4.2 Create Face

The Create Face command button allows you to perform the following operations.

The following sections describe the purpose and operation of each of the commands listed above.

The Create Real Rectangular Face command creates a real planar face in the shape of a rectangle.

When you execute the Create Real Rectangular Face command, GAMBIT creates a real rectangular, planar face. GAMBIT orients and locates the face such that it is aligned with one of the coordinate planes of a specified reference coordinate system. The Create Real Rectangular Face command includes the following input parameters:

• Width
• Height
• Coordinate Sys.
• Direction

The Width and Height parameters determine the dimensions of the rectangular face. (NOTE: If you do not specify the Height parameter, GAMBIT creates a square face with sides of the length specified by the Width parameter (and vice versa)). The Coordinate Sys. parameter specifies the reference coordinate system for the face creation operation. The Direction parameter specifies the orientation and location of the face relative to the reference coordinate system.

To open the Create Real Rectangular Face form (see below), click the Create Real Rectangular Face command button on the Geometry/Face subpad.

The Create Real Rectangular Face form includes the following specifications.

The Create Real Circular Face command creates a real planar face in the shape of a circle.

When you execute the Create Real Circular Face command, GAMBIT creates a real circular, planar face. GAMBIT orients and locates the face such that it is aligned with one of the coordinate planes of a specified reference coordinate system. The Create Real Circular Face command includes the following input parameters:

• Radius
• Coordinate Sys.
• Plane

The Radius parameter determines the size of the circular face. The Coordinate Sys. parameter specifies the reference coordinate system for the face creation operation. The Plane parameter specifies the orientation of the face relative to the reference coordinate system. (NOTE: The created face is always centered at the origin of the reference coordinate system.)

To open the Create Real Circular Face form (see below), click the Create Real Circular Face command button on the Geometry/Face subpad.

The Create Real Circular Face form includes the following specifications.

The Create Real Elliptical Face command creates a real planar face in the shape of an ellipse.

When you execute the Create Real Elliptical Face command, GAMBIT creates a real elliptical, planar face. GAMBIT orients and locates the face such that it is aligned with one of the coordinate planes of a specified reference coordinate system. The Create Real Elliptical Face command includes the following input parameters:

• Radius 1
• Radius 2
• Coordinate Sys.
• Plane

Radius 1 and Radius 2 represent the lengths of the major and minor axes of the ellipse. For the purposes of this command, the major and minor axes are always aligned with the coordinate axes of the plane in which the elliptical face is created. Either parameter, Radius 1 or Radius 2, can serve as the major or minor axis of the ellipse. (NOTE: If you do not specify Radius 2, GAMBIT creates a circular face of radius Radius 1.)

The Coordinate Sys. parameter specifies the reference coordinate system for the face creation operation. The Plane parameter specifies the orientation of the face relative to the reference coordinate system. (NOTE: The created face is always centered at the origin of the reference coordinate system.)

To open the Create Real Elliptical Face form (see below), click the Create Real Elliptical Face command button on the Geometry/Face subpad.

The Create Real Elliptical Face form includes the following specifications.

2.4.3 Boolean Operations

The Boolean Operations command button allows you to perform the following operations.

Each of the commands listed above allows you to perform a Boolean operation involving two or more faces. The specified faces do not have to be planar, but they must be coincident in the intersecting region between them. (NOTE: For the lone exception to this rule, see "Unite Real Faces," below.)

Figure 2-74: Boolean face operations

Each Boolean operation form includes at least one Retain option. When you perform a Boolean operation involving a set of specified faces, GAMBIT replaces the specified faces with a single face that constitutes the result of the operation. If you select the Retain option, GAMBIT retains the original faces when it performs the Boolean operation.

The Unite Real Faces command allows you to unite two or more overlapping faces into one or more real faces.

When you unite overlapping faces by means of the Unite Real Faces command, GAMBIT creates one real face that represents the union of the overlapping faces. If you specify a set of faces on the Unite Real Faces form such that the set consists of two or more subsets of faces that overlap each other but do not overlap the faces of any other subset, GAMBIT creates a separate real face for each subset.

Using the Unite Real Faces Form

To open the Unite Real Faces form (see below), click the Unite command button on the Geometry/Face subpad.

The Unite Real Faces form includes the following specifications.

The Subtract Real Faces command allows you to perform a Boolean subtraction involving two or more real faces.

To open the Subtract Real Faces form (see below), click the Subtract command button on the Geometry/Face subpad.

The Subtract Real Faces form includes the following specifications.

Intersect Real Faces

The Intersect Real Faces command allows you to perform a Boolean intersection of two or more real faces.

To open the Intersect Real Faces form (see below), click the Intersect command button on the Geometry/Face subpad.

The Intersect Real Faces form includes the following specifications.

2.4.4 Connect/Disconnect Faces

The Connect/Disconnect Faces command button allows you to perform two operations.

The following sections describe the procedures and specifications required to execute the operations listed above.

NOTE: The Specify Color Mode command button on the Graphics/Windows Control toolpad allows you to display model colors based on entity connectivity rather than topology. For a description of the use of the Specify Color Mode command button, see the GAMBIT User's Guide, Section 3.4.2.

Connect Faces

The Connect Faces command allows you to connect two or more faces. (NOTE: If you connect two or more meshed faces, and the meshes on each face are topologically identical to each other, GAMBIT preserves the meshes when connecting the faces.)

To connect faces, you must specify the following parameters:

• Two or more faces to be connected
• The connection type

Specifying the Faces to Be Connected

The faces to be connected can be real or virtual, but they are subject to certain restrictions imposed by the connection type (see below).

Specifying the Connection Type

There are four types of face connection operations:

• Real
• Virtual (Forced)
• Virtual (Tolerance)
• Real and Virtual (Tolerance)

The following sections describe the basic features of each connection type.

Specifying a Real Connection

The Real option allows you to connect coincident real faces--that is, two or more real faces the edges of which are coincident. When you connect real faces and specify the Real option, GAMBIT deletes all but one of the specified faces and connects the remaining real face to any and all volumes of which the deleted faces were a part.

Specifying a Virtual (Forced) Connection

The Virtual (Forced) option allows you to connect real and/or virtual faces, regardless of their proximity to each other. When you connect faces and specify the Virtual (Forced) option, GAMBIT replaces the specified faces with a virtual face. If a specified face constitutes part of a volume, GAMBIT overlays the volume with a virtual volume and forms the virtual volume according to the shape and position of the new virtual face.

Specifying a Virtual (Tolerance) Connection

The Virtual (Tolerance) option allows you to specify that only those real and/or virtual faces the edges of which are near to each other to within a specified tolerance are connected. There are two ways to express the tolerance value:

• Tolerance
• Shortest Edge%

The Tolerance specification represents the tolerance value as expressed in absolute distance units. The Shortest Edge% specification represents the tolerance value expressed as a percentage of the length of the shortest edge.

Specifying a Real and Virtual (Tolerance) Connection

When you specify the Real and Virtual (Tolerance) option, GAMBIT performs the following two operations in sequence:

1. Real connect operations for faces that are coincident to within the global tolerance value
2. Virtual (Tolerance) connect operations for unconnected, specified faces that are near to each other to within the user-specified tolerance

Using the Connect Faces Form

To open the Connect Faces form (see below), click the Connect command button on the Geometry/Face subpad.

The Connect Faces form includes the following specifications.

Disconnect About Real Face

The Disconnect About Real Face command allows you to disconnect individual real faces and/or volumes that share a common face.

When you disconnect faces, GAMBIT creates a new face for all but one of the entities to which the specified face is connected. For example, if the specified face is shared by three volumes, GAMBIT creates two new faces that are coincident with the specified face and connects them to two of the three volumes. The original face is connected to the remaining volume.

Specifying the Edge and Vertex Options

GAMBIT provides the following three options with respect to the treatment of endpoint vertices for the disconnected edges:

• Face + Edges/Vertices
• Face Only
• Face + Selected Edges

The following table describes the effects associated with each option.

Using the Disconnect About Real Face Form

To open the Disconnect About Real Face form (see below), click the Disconnect command button on the Geometry/Face subpad.

The Disconnect About Real Face form includes the following specifications.

2.4.5 Modify Face Color/Label

The Modify Face Color/Label command button allows you to perform two operations.

The following sections describe the procedures and specifications required to execute the operations listed above.

Modify Face Color

The Modify Face Color command allows you to change the displayed color of the geometry and/or mesh and/or shading associated with one or more faces.

Using the Modify Face Color Form

To open the Modify Face Color form (see below), click the Modify Color command button on the Geometry/Face subpad.

The Modify Face Color form includes the following specifications.

For specific instructions on setting colors, see "Using the Set Color Form" in Section 2.2.4.

Modify Face Label

The Modify Face Label command allows you to change the label associated with any face.

Using the Modify Face Label Form

To open the Modify Face Label form (see below), click the Modify Label command button on the Geometry/Face subpad.

The Modify Face Label form includes the following specifications.

2.4.6 Move/Copy/Align Faces

The Move/Copy/Align Faces command button allows you to perform two operations.

The following sections describe the procedures and specifications required to execute the operations listed above.

Move/Copy Faces

The Move/Copy Faces command allows you to reposition and/or reorient one or more faces or to create copies of faces. For a general description of the procedures and specifications required to move and/or copy entities, see "Moving an Entity" and "Copying an Entity," respectively, in Section 2.1.4.

Using the Move/Copy Faces Form

To open the Move/Copy Faces form (see below), click the Move/Copy command button on the Geometry/Face subpad.

For a complete description of the specifications available on the Move/Copy Faces form, see "Using Move/Copy Forms" in Section 2.1.4.

Align Faces

The Align Faces command allows you to reposition and/or reorient a face so that it coincides with another face or is aligned with a plane defined by three vertices. (For a general description of the procedure and specifications required to align an entity, see "Aligning an Entity," in Section 2.1.4, above.)

Using the Align Faces Form

To open the Align Faces form (see below), click the Align command button on the Geometry/Face subpad.

For a complete description of the specifications available on the Align Faces form, see "Using Align Forms" in Section 2.1.4.

2.4.7 Split/Merge/Collapse/Simplify Faces

The Split/Merge/Collapse/Simplify Faces command button allows you to perform the following operations.

The following sections describe the procedures and specifications required to execute the operations listed above.

Split Face

To split a face by means of the Split Face command, you must specify the fol­lowing parameters:

• Target face
• Split type

Specifying the Target Face

GAMBIT allows you to split either real or virtual faces by means of the Split Face operation but places the fol­low­ing restrictions on the type of faces that can be created from the split:

• If you split a real face, GAMBIT can create real or non-real faces.
• If you split a non-real face, GAMBIT creates only non-real faces.

GAMBIT provides the following types of face-split options:

• Face (Real)
• Face (Faceted)
• Edges (Virtual)
• Vertices (Virtual)

Specifying a Face (Real) Split Operation

The Face (Real) split option allows you to split a real target face using a real split-tool face. (NOTE: You cannot use the Face (Real) option to split a non-real face.) When you split a face using the Face (Real) split option, GAMBIT creates a set of real faces from the split operation.

The general rules that govern the relationship between the target and split-tool faces for a Face (Real) split operation are as follows:

• The split-tool face must fully or partially intersect the target face. The extent of intersection between the split-tool face and the target face determines the types of edges and faces created from the split opera­tion as follows (see Figure 2-75):
  • If the split-tool face fully intersects the face to be split, GAMBIT creates two faces that share a common edge representing the curve of intersection (see Figure 2-75(a)).
  • If the split-tool face partially intersects the face to be split, GAMBIT creates a single face that includes a dangling edge (see Figure 2-75(b)).
  

  Figure 2-75: Effect of fully and partially intersecting split-tool faces

• If the face to be split is part of an existing volume, you must spec­ify the Connected suboption (see below).

• Retain
• Connected

If you specify the Connected option, GAMBIT connects the faces that result from the split operation along their common edge(s). If you do not specify the Connected option, the split operation creates disconnected faces.

Specifying a Face (Faceted) Split Operation

The Face (Faceted) split option allows you to split a faceted target face using a faceted split-tool face—that is, the Face (Faceted) split operation cannot be used to split real or virtual target faces or to split a faceted face with a real or virtual split-tool face.

The Face (Faceted) operation includes a Retain option. If you specify the Retain option, GAMBIT retains the split-tool face upon completion of the split operation. If you do not specify the Retain option, GAMBIT deletes the split-tool face.

Specifying an Edges (Virtual) Split Operation

The Edges (Virtual) split option allows you to split a real or non-real target face using a split-tool consisting of one or more real or non-real edges. Regardless of the type(s) of edge(s) used in the operation, the Edge (Virtual) split operation produces only connected, virtual faces.

The Edges (Virtual) split-tool can consist of either a single edge or of a chain of connected edges. In either case, the endpoints of the split-tool edge or outermost endpoints of the split-tool chain must comprise components of the boundary for the target face. If you specify a chain of connected edges as the split tool, GAMBIT transforms the chain into a single, virtual edge along which the faces that result from the split operation are connected.

The Edges (Virtual) split option includes a Tolerance suboption that allows you to specify an allowable tolerance between the split-tool edge or edge-chain and the surface of the target face.

Specifying a Vertices (Virtual) Split Operation

The Vertices (Virtual) split option allows you to split a real or non-real target face using a split-tool consisting of two or more real or non-real vertices. Regardless of the type(s) of vertices used in the operation, the Vertices (Virtual) split operation produces connected, virtual faces.

The Vertices (Virtual) split-tool can consist of either a pair of vertices or a series of vertices located on the surface of the face. In either case, the vertex pair or outermost endpoints of the vertex series must comprise components of the boundary for the target face. If you specify a series of vertices as the split tool, GAMBIT transforms the series into a chain of straight virtual edges that serves as the boundary between the faces resulting from the split operation.

The Vertices (Virtual) split option includes two suboptions:

• Tolerance
• Shaped Edge

The Shaped Edge suboption specifies that the edge resulting from the split operation is shaped such that it bisects the face boundary at its endpoints (see Figure 2-76).

Figure 2-76: Effect of Shaped Edge option

NOTE: The Shaped Edge option is available for the Vertices (Virtual) operation only when the face is split by two vertices. If you specify more than two vertices for the Vertices (Virtual) face split operation, GAMBIT creates a chain of straight virtual edges that serves as the boundary between the faces resulting from the split operation.

Using the Split Face Form

To open the Split Face form (see below), click the Split command button on the Geometry/Face subpad.

Face	specifies the face to be split.
Split with	-------------------------
Face (Real) Face (Faceted) Edges (Virtual) Vertices (Virtual)	specifies the split type.

The specifications available on the lower section of the Split Face form depend on the specified Split with option as follows.

Face (Real) Split Option

When you specify the Face (Real) option, the lower section of the Split Face form appears as shown above and includes the following specifications.

Face	specifies the real face that constitutes the split tool.
Retain	specifies retaining the split-tool face at the conclusion of the split operation.
Connected	specifies connecting the edge(s) that constitute(s) the boundary between the faces resulting from the split operation.

Face (Faceted) Split Option

When you specify the Face (Faceted) option, the lower section of the Split Face form appears as shown below and includes the following specifications.

Face	specifies the faceted face that constitutes the split tool.
Retain	specifies retaining the split-tool face at the conclusion of the split operation.

Edges (Virtual) Split Option

When you specify the Edges (Virtual) option, the lower section of the Split Face form appears as shown below and includes the following specifications.

Edges	specifies the real or non-real edge(s) that constitute(s) the split tool.
Tolerance	specifies that the split operation is performed if the split-tool edges are located in proximity to the face to within the specified tolerance value.

Vertices (Virtual) Split Option

When you specify the Vertices (Virtual) option, the lower section of the Split Face form appears as shown below and includes the following specifications.

Vertices	specifies the real or non-real vertices that constitute the split tool.
Tolerance	specifies that the split operation is performed if the split-tool vertices are located in proximity to the face to within the specified tolerance value.
Shaped Edge	shapes the resulting splitting edge so that it is normal to the face boundary edges at its endpoints.

Merge Faces (Virtual)

The Merge Faces (Virtual) command allows you to merge two or more real and/or virtual faces into a single virtual face. (NOTE: If you merge faces that possess identical boundary-zone type specifications, GAMBIT retains the specification and assigns it to the face that results from the merge operation. If the faces differ with respect to their boundary-zone specifications, GAMBIT does not assign a specification to the resulting face.)

To merge faces by means of the Merge Faces (Virtual) command, you must specify the following parameters:

• The set of faces to be merged
• The merge type
• The Merge edges option

Specifying the Faces to Be Merged

GAMBIT allows you to merge two or more real and/or virtual faces into a single virtual face but applies the following rules with respect to the set of faces to be merged:

• Each face in the set must be connected by means of a common edge to at least one other face in the set
• None of the connected, common edges between faces are allowed to be connected to faces that are not in the set of faces to be merged

Specifying the Merge Type

When you merge faces, you must specify the merge type. There are two types of face-merge operations:

• Virtual (Forced)
• Virtual (Tolerance)

When you specify a Virtual (Forced) merge, GAMBIT merges all of the faces in the specified set, regardless of the lengths of their sides. (NOTE: GAMBIT does not allow you to merge faces oriented such that they form sharp angles. You can set the angle criteria by means of the Edit Defaults form (default = 90).) When you specify a Virtual (Tolerance) merge, GAMBIT performs the merge operation only if all edges in the set meet specified tolerance criteria.

Virtual (Tolerance) Criteria

There are two types of face-merging Virtual (Tolerance) criteria:

• Max. Distance
• Min. Angle

The Max Distance criterion is based on a theoretical plane fit through all faces specified for the merge operation. When you specify the Virtual (Tolerance) option, GAMBIT includes in the merge operation only those faces that are located near the theoretical plane to within the specified distance.

The Min Angle criterion is based on the internal angles between pairs of neighboring faces. When you specify the Virtual (Tolerance) option, GAMBIT merges only those face pairs the internal angle of which is greater than the specified tolerance. For example, to merge two side faces of a regular, six-sided prism using the Virtual (Tolerance) option, you must specify a Min Angle value of 119°.

Specifying the Merge edges Option

When you specify the Merge edges option, GAMBIT merges the edges that result from the face-merge operation. As an example of the effect of the Merge edges option, consider the two square, coplanar faces shown in Figure 2-77, which are connected by means of edge.1.

• If you do not specify the Merge edges option when merging the square, coplanar faces, GAMBIT creates a four-sided face bounded by six edges (see Figure 2-78(a)).
• If you specify the Merge edges option, GAMBIT merges the pairs of edges that constitute the upper and lower sides of the four-sided face, thereby creating a face bounded by only four edges (see Figure 2-78 (b)).

Figure 2-77: Face merge—effect of Merge edges option, original faces

Figure 2-78: Face merge—effect of Merge edges option, merged faces

Using the Merge Faces (Virtual) Form

To open the Merge Faces (Virtual) form (see below), click the Merge command button on the Geometry/Face subpad.

The Merge Faces (Virtual) form includes the following specifications.

Collapse Faces (Virtual)

The Collapse Face (Virtual) command allows you to collapse a real or virtual face that lies between two or more neighboring real and/or virtual faces.

When you collapse a face, GAMBIT performs the following operations:

1. Split the face into two or more faces of approximately equal size.
2. Merge the resulting faces with their specified neighboring faces.

Each of the neighboring faces specified for the collapse operation must be connected to the face to be collapsed by means of one or more common edges. The virtual faces that result from the collapse operation share the virtual edge or vertex that replaces the collapsed face.

The following sections illustrate the results of the face collapse operation for three different situations involving planar faces.

Three Coplanar Faces in a Line

In Figure 2-79, three square faces—labeled face.1, face.2, and face.3—are arranged in a line, and face.2 is connected to face.1 and face.3 at edge.4 and edge.8, respectively. The face-collapse operation replaces face.2 with a virtual edge (v_edge.11) and overlays two virtual faces (v_face.4 and v_face.5) onto face.1 and face.3.

Figure 2-79: Face collapse—3 coplanar faces arranged in a line

Three Coplanar Faces at an Angle

In Figure 2-80, three square faces are arranged at an angle with respect to each other. As in the previous example, the face-collapse operation replaces face.1 with a virtual edge and overlays two virtual faces onto face.1 and face.3.

Figure 2-80: Face collapse—3 coplanar faces arranged at an angle

Four Non-coplanar Faces

In Figure 2-81, a triangular face is surrounded by three faces that are arranged at right angles with respect to each other. The face-collapse operation replaces face.4 with a virtual vertex (v_vertex.12), and overlays three virtual faces that share the vertex.

Figure 2-81: Face collapse—4 non-coplanar faces

Face Collapse Specifications

To collapse a face by means of the Collapse Face (Virtual) form, you must specify the following parameters:

• The face to be collapsed
• The neighboring faces between which the face is to be collapsed

The following general rules govern the specifications of parameters for the face-collapse operation:

• You cannot collapse a face that constitutes part of a volume. For example, GAMBIT does not allow you to collapse one end of a prism.
• Each of the specified neighboring faces must be connected to the face to be collapsed by means of a common edge.

Using the Collapse Face (Virtual) Form

To open the Collapse Face (Virtual) form (see below), click the Collapse command button on the Geometry/Face subpad.

The Collapse Face (Virtual) form includes the following specifications.

Simplify Faces

The Simplify Faces command removes (deletes) dangling edges from faces. Dangling edges are edges that are included in the list of edges that define a face but which do not constitute necessary parts of the closed edge loop that circumscribes the face. They most often result from face-split operations in which the split-tool face only partially intersects the target face (see “Split Face,” above).

Figure 2-82 shows two different types of dangling edges, both of which can be removed by means of the Simplify Faces command. In Figure 2-82(a), the dangling edge is connected to the boundary-edge loop of its associated face. In Figure 2-82(b), the dangling edge exists apart from and is not connected to the boundary even though it is included in the list of edges associated with the face.

Figure 2-82: Faces that include dangling edges

Using the Simplify Faces Form

To open the Simplify Faces form (see below), click the Simplify command button on the Geometry/Face subpad.

The Simplify Faces form includes the following specification.

2.4.8 Heal Real Faces/Convert Faces

The Heal Real Faces/Convert Faces command button allows you to perform two operations.

The following sections describe the procedures and specifications required to execute the operations listed above.

Heal Real Faces

The Heal Real Faces command attempts to heal geometry and topology problems that sometimes occur in sets of real faces.

In most cases, model geometry data generated from within GAMBIT automatically meet the stringent integrity standards required by the ACIS modeler. However, several GAMBIT operations-for example, Boolean operations-can sometimes produce geometry that fails to meet the ACIS standards. In addition, geometry imported to GAMBIT from outside sources may not meet such standards due to any of the following factors:

• Inherent numerical limitations in the system used to generate the geometry


• Limitations of data transfer through neutral file formats


• Differences in tolerance settings between the model-generating program and GAMBIT

NOTE: The GAMBIT healing operations—Heal Real Faces and Heal Real Volume (see Section 2.5.8)—are not guaranteed to correct all geometry and topology problems in the model. In general, both operations should be used with caution, because they are not robust and sometimes produce peculiar model geometry.

Specifying the Heal Real Faces Options

As noted above, the healing operation involves three steps:

• Geometry simplification
• Stitching
• Geometry building

GAMBIT allows you to control the geometry simplification and stitching steps by means of the Geometry simplification and Stitch faces options, respectively, on the Heal Real Faces form.

Geometry simplification Option

The Geometry simplification option allows you to specify whether or not GAMBIT employs geometry simplification when healing faces. If you select the Geometry simplification option, you can also specify a Tolerance value. The Tolerance value is used to determine whether or not NURBS surfaces can be approximated by analytic surfaces. If the Geometry simplification Tolerance is too loose, approximate analytic fits to NURBS geometry may be obtained. In such cases, the gaps between surfaces may increase, and healing in subsequent steps may be more difficult or may fail.

Stitch faces Option

The Stitch faces option allows you to specify whether or not GAMBIT stitches faces during the healing operation. If you select the Stitch faces option, you can also specify Minimum tolerance and Maximum tolerance values. The Minimum tolerance and Maximum tolerance values specify the range in which GAMBIT performs stitching between edges. GAMBIT begins stitching at the Minimum tolerance value and increases in steps toward the Maximum tolerance value.

At each step, GAMBIT stitches only those edges the lengths of which are greater than the current tolerance value. Consequently, the Minimum tolerance must be smaller than the length of the shortest edge in the model. The Maximum tolerance value represents the maximum gap size for which GAMBIT performs stitching.

Repairing Gaps Between Faces

Figure 2-83: Heal Real Faces operation on faces with boundary edge gaps

Figure 2-84: Heal Real Faces operation-volume creation

Convert Faces

The Convert Faces command converts one or more non-real (faceted and/or virtual) faces to real faces. The conversion process preserves both the topology and any existing mesh(es) associated with the converted face(s). In addition, all non-real edges and vertices associated with the face(s) are converted to real edges and vertices.

NOTE (1): Only non-real faces that include a mapped mesh can be converted to real faces.

NOTE (2): Hidden entities that serve as hosts for virtual entities may become active (that is, visible) when their guest entities are converted to real geometry.

Using the Convert Faces Form

2.4.9 Summarize/Check/Query Faces and Total Entities

The Summarize/Check/Query Faces and Total Entities command button allows you to perform the following operations.

The following sections describe the procedures and specifications required to execute the operations listed above.

Summarize Faces

The Summarize Faces command displays face summary information in the Transcript window.

Using the Summarize Faces Form

To open the Summarize Faces form (see below), click the Summarize command button on the Geometry/Face subpad.

The Summarize Faces form includes the following specifications.

Faces	specifies the faces for which information is to be summarized in the Transcript window.
All Pick	All specifies all faces in the model. Pick specifies faces selected by means of the Faces list box. (NOTE: If you pick a face in the graphics window or click in the Faces list box, GAMBIT automatically selects the Pick option.)

Check Faces

The Check Faces command assesses the topological and/or geometrical validity of faces in the model and summarizes the results in the Transcript window.

When you execute the Check Faces command, GAMBIT checks the model to determine its validity with respect to either or both of the following types of characteristics:

• Topology
• Geometry

Topology refers to the spatial relationships between entities. Geometry refers to proximity and shape characteristics of the model.

Topology Check

Topological validity is an assessment of the underlying organization of the model-for example, the correct associations between a face entity and the edges that comprise its boundaries or between entities that are associated with each other by virtue of a virtual-geometry, guest-host relationship.

For a given face, the Check Faces topology check operation examines the model to ensure that it meets the following criteria:

• Lower-topology edges are in separate loops.
• Lower-topology edges are visible and correctly reference the face.
• Sense information (in the form of co-edges) exists for all edges.
• Upper-topology volumes correctly reference the face.
• Upper-topology volumes maintain correct sense information for the face (in the form of co-faces).
• Virtual guest entities correctly reference the face as a host.

NOTE: Failure of the topology check for any face in the model constitutes a serious problem for the model as a whole. GAMBIT does not currently include any tools that allow you to repair problems that cause failures of topology checks.

Geometry Check

Geometrical validity is an assessment of the model with respect to proximity and shape characteristics-such as the distances between connected edges and/or the mathematical continuity of model curves and surfaces. The Check Faces geometry check criteria are as follows:

• All real faces correctly reference the ACIS model.
• No real faces exhibit problems related to continuity, self-intersection, bad closure, degeneracies, or singularities.
• Any virtual-face hosts are of the correct type. For example, a virtual face formed by connecting or merging two faces must reference only the two faces as hosts. Similarly, a virtual face defined on a volume must not be hosted by a face, and a virtual face formed by splitting a face must be hosted by the face that is split. (NOTE: The face geometry check operation also checks the validity of host geometry.)

NOTE: Face-check errors may not represent a serious problem for certain geometry or meshing operations. For example, a face may be meshable even if other operations-such as Boolean operations-fail.

It is sometimes possible to repair geometry errors for faces by means of face- or volume-healing operations (see Sections 2.4.7 and 2.5.8, respectively). Healing processes operate on a set of faces (which may belong to a volume) by modifying geometry near edge and vertex boundaries so that the geometry is within tolerance. Healing operations do not modify regions distant from edge or vertex boundaries. When edges or vertices of different faces are located near to each other, healing operations attempt to modify the geometry in order to connect these edges or vertices.

Using the Check Faces Form

To open the Check Faces form (see below), click the Check command button on the Geometry/Face subpad.

The Check Faces form includes the following specifications.

Faces	specifies the faces to be included in the checking operations.
All Pick	All specifies all faces in the model. Pick specifies faces selected by means of the Faces list box. (NOTE: If you pick a face in the graphics window or click in the Faces list box, GAMBIT automatically selects the Pick option.)
Check Topology	specifies a topology check on the selected faces.
Check Geometry	specifies a geomtery check on the selected faces.

Query Faces

The Query Faces command allows you to identify the locations and/or the names of specific faces.

Using the Query Faces Form

To open the Query Faces form (see below), click the Query command button on the Geometry/Face subpad.

For a general description of using the Query Faces form, see "Using the Query Vertices Form" in Section 2.2.7, above.

Total Entities

The Total Entities command displays in the Transcript window the total number of geometry and/or mesh entities that currently exist in the model. For example, if you select only the Geometry entities option on the Total Entities form and click Apply, GAMBIT displays in the Transcript window the total numbers of vertices, edges, faces, volumes, groups, and coordinate systems that currently exist in the model.

Using the Total Entities Form

For a description of the options available on the Total Entities form, see "Total Entities," in Section 2.2.7.

2.4.10 Delete Faces

The Delete Faces command deletes one or more faces from the model.

The Delete Faces operation is subject to the following restrictions:

• GAMBIT does not allow you to delete faces that constitute parts of a volume.
• If you delete a virtual face that constitutes the connection of two or more real or virtual faces, GAMBIT restores those faces to the model when it deletes the specified face.

Retaining Face Edges

By default, when you delete a face, GAMBIT deletes the edges that constitute parts of the face as well as their endpoint vertices. To retain the edges and vertices when the face is deleted, unselect the Lower Geometry option at the bottom of the Delete Faces form. When you delete a face and retain its edges, the edges remained connected to each other by means of their common endpoint vertices.

Retaining and Deleting Associated Vertices

When you delete a face with associated vertices created by means of the Create Vertex On Face command, GAMBIT retains or deletes the vertices depending on whether they are real or virtual entities, respectively. For example, if you delete a face that is associated with one real vertex and one virtual vertex—both of which were created by means of the Create Vertex On Face command—GAMBIT retains the real vertex and deletes the virtual vertex. (The virtual vertex cannot exist without the host face.)

Deleting Virtual Faces

Using the Delete Faces Form

To open the Delete Faces form (see below), click the Delete command button on the Geometry/Face subpad.

The Delete Faces form includes the following specifications.

© Fluent, Inc. 12/10/01