The following commands are available on the Geometry/Edge subpad.
The Create Edge command button allows you to perform the following operations.
The Create Straight Edge operation (edge create straight command) creates one or more straight edges between any two or more existing vertices. The created edges can be real or virtual.
The Create Straight Edge command requires the following input parameters:
To create an edge by means of the Create Straight Edge command, you must specify two vertices that comprise the endpoints of the edge. GAMBIT defines the sense of the edge based on the order in which the vertices are specified. The edge sense points from the first (start) vertex to the second (end) vertex (see Figure 230).
Figure 230: Straight edge specifications
If you specify more than two vertices on the Create Straight Edge form, GAMBIT creates multiple edges from a single operation. The order in which the vertices are specified determines the locations and connectivity of the created edges. For example, if you specify (in order) three vertices labeled vertex.1, vertex.7, and vertex.3 for a Create Straight Edge operation, GAMBIT creates two edges defined as follows.
Edge  Start Vertex  End Vertex 
edge.1  vertex.1  vertex.7 
edge.2  vertex.7  vertex.3 
Note that the two edges defined in the table above are connected to each other by means of vertex.7.
The Create Straight Edge command allows you to create either real or virtual edges. The geometry type (real or virtual) of the created edge is subject to the following constraints for vertex specification.
If you create a virtual edge by means of the Create Straight Edge command, GAMBIT allows you to specify whether the virtual edge is hosted or unhosted. Hosted edges possess guesthost relationships with existing volumes, faces, or edges. Unhosted edges exist on their own and do not possess guesthost relationships with any other entities in the model.
To open the Create Straight Edge form (see below), click the Create Straight Edge command button on the Geometry/Edge subpad.
The Create Straight Edge form includes the following specifications.
Vertices  specifies the vertices that constitute the endpoints of the edges. 
Type:  
Real  creates a real edge. 
Virtual  creates a virtual edge. If you choose the Virtual option, you can also specify a host edge, face, or volume for the virtual edge. 
Host  specifies that any created virtual edges are hosted by an existing volume, face, or edge. 
Volume Face Edge 
specifies the host entity type. 
Volume Face Edge 
specifies the host entity name. 
Label  specifies a label for the new edge. (See Section 2.1.1.) 
The Create Circular Arc operation (edge create arc command) creates an edge in the shape of a circular arc. You can also use the Create Circular Arc command to create a spiral arc (see "Method 1—Center Vertex and Two Endpoint Vertices," below).
GAMBIT provides three methods for creating a circular arc edge. Two methods require you to specify three existing vertices to define the size and location of the arc. The other method requires the specification of the arc radius, angle, center, and coordinate plane. The input parameters associated with each method are as follows.
Method  Parameters 
1 

2 

3 

Methods 1 and 2 can be used to create either real or virtual edges. The type of edge (real or virtual) created by each method depends on the types of vertices specified to define the edge endpoints (see below). Method 3 produces only real edges.
To create an arc edge by means of Method 1, you must specify one Center vertex, two EndPoints vertices, and the arc segment (major or minor) along which the edge is to be constructed (see Figure 231). If either of the EndPoints vertices is a virtual vertex, GAMBIT creates a virtual edge; otherwise GAMBIT creates a real edge.
Figure 231: Circular arc edge specifications—Method 1
You can use Method 1 to create either a circular or spiral arc edge. The shape of the created arc edge depends on the relative distances of the EndPoints vertices from the Center vertex as follows.
Figure 232: Effect of EndPoints vertex locations on arc edge shape
Figure 233: Effect of arcsegment specification on edge shape
To create a circular arc edge by means of Method 2, you must specify three vertices each of which lies on the circle that defines the size and shape of the arc. GAMBIT constructs the edge from the first specified vertex through the second specified vertex to the third specified vertex (see Figure 234). Therefore, the first and third specified vertices constitute the endpoints of the edge. If either of the endpoint vertices is a virtual vertex, GAMBIT creates a virtual edge; otherwise, GAMBIT creates a real edge.
Figure 234: Circular arc edge specifications—Method 2
To create a circular arc edge by means of Method 3, you must specify the following parameters (see Figure 235). (NOTE: Method 3 produces only real edges.)
Figure 235: Circular arc edge specifications—Method 3
The Radius, Start Angle, and End Angle specifications define the size and sweep of the arc. The Center vertex specification defines the global location of the arc. (NOTE: If you do not specify a Center vertex, GAMBIT locates the center of the arc at the center of the currently active coordinate system.) The Plane specification defines the coordinate plane in which the arc lies.
To open the Create Circular Arc form (see below), click the Create Circular Arc command button on the Geometry/Edge subpad.
The Create Circular Arc form includes the following specifications.
Method: contains three radio buttons that allow you to specify the method by which the arc is created. The methods are briefly described as follows.
Vertex:  
Center  specifies the vertex that constitutes the center of the arc. 
EndPoints  specifies the vertices that constitute the endpoints of the arc. 
Arc:  allows you to specify whether the created edge represents the major or minor arc between the endpoints. 
Label  (both methods) specifies a label for the new edge. (See Section 2.1.1.) 
When you specify Method 2 for the creation of a circular arc edge, the middle section of the Create Circular Arc form appears as shown below.
Vertices  specifies the three vertices that lie on the arc. 
When you specify Method 3 for the creation of a circular arc edge, the middle section of the Create Circular Arc form appears as shown below.
Radius  specifies the radius of the arc. 
Start Angle  specifies the start angle for the arc as measured from one of the two coordinate axes on the selected coordinate plane. 
End Angle  specifies the end angle for the arc. 
Center  specifies a vertex that defines the center of the arc. 
Plane  
XY YZ ZX 
specifies the coordinate plane in which the arc lies. 
The Create Full Circle operation (edge create circle command) creates an edge in the shape of a full circle.
GAMBIT provides two methods for creating an edge 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.
Figure 236: Fullcircle edge specifications
The Create Full Circle command can be used to create either a real edge or a virtual edge. The type of edge created depends on the vertex types as follows:
To open the Create Full Circle form (see below), click the Create Full Circle command button on the Geometry/Edge subpad.
The Create Full Circle form includes the following specifications.
Method:  contains two radio buttons that allow you to specify the method by which the circle is created. For either method, you must specify three vertices. The two methods differ in their treatment of the vertices as follows.

The center section of the Create Full Circle form varies according to the method selected to construct the circle. The specifications available on the center section of the form are as follows.
Vertices:  
Center  specifies the vertex that constitutes the center of the circle. 
EndPoints  specifies the vertices that lie on the circle. 
Label  (both methods) specifies a label for the new edge. (See Section 2.1.1.) 
When you specify Method 2 for the creation of a full circle, the middle section of the Create Full Circle form appears as shown below.
Vertices  specifies the three vertices that lie on the circle. 
The Create Elliptical Arc operation (edge create ellipse command) creates an edge in the shape of an elliptical arc.
To create an elliptical arc edge, you must specify the following parameters (see Figure 237).
Figure 237: Elliptical arc edge specifications
The Center, Major, and On Edge vertices define the shape and size of the full ellipse of which the arc edge is a part. (NOTE: The three vertices that define the ellipse must not be collinear.) The Start angle and End angle define the length of the edge as well as its angular position relative to a reference vector constructed from the Center vertex to the Major vertex.
The Create Elliptical Arc command can be used to create either a real edge or a virtual edge. The type of edge created is determined by the Major vertex type. Specifically, if the Major vertex is a virtual vertex, GAMBIT creates a virtual edge; otherwise, GAMBIT creates a real edge.
To open the Create Elliptical Arc form (see below), click the Create Elliptical Arc command button on the Geometry/Edge subpad.
The Create Elliptical Arc form includes the following specifications.
Vertex:  
Center  specifies the vertex that constitutes the center of the ellipse. 
Major  specifies the vertex that defines the major axis of the ellipse. 
On Edge  specifies a vertex that lies on the edge of the full ellipse. If a vector drawn from the Center vertex to the On Edge vertex is at right angles to a vector drawn from the Center vertex to the Major vertex, then the distance between the Center vertex and the On Edge vertex exactly defines the length of the minor axis. 
Angle:  allows you to specify the angle encompassed by the elliptical edge. The zeroangle reference vector points from the Center vertex to the Major vertex. 
Start  specifies the start angle for the elliptical arc. 
End  specifies the end angle for the elliptical arc. 
Label  specifies a label for the new edge. (See Section 2.1.1.) 
The Create Conic Arc operation (edge create conic command) creates an edge in the shape of a conic arc.
To create a conic arc edge, you must specify the following parameters (see Figure 238):
Figure 238: Conic edge specifications
The Start, Shoulder, and End vertices specify the location and sense of the conic arc edge. The sense of the edge points from the Start vertex to the End vertex.
The Shoulder vertex constitutes the apex of the conic arc, and its position of the Shoulder vertex determines whether or not the conic edge is symmetric with respect to the Start and End vertices. If the Shoulder vertex is equidistant from the Start and End vertices (as shown in Figure 238) then the conic arc edge is symmetric.
The Create Conic Arc command can be used to create either a real edge or a virtual edge. The type of edge created is determined by the Start and End vertex types. Specifically, if either the Start or End vertex is a virtual vertex, GAMBIT creates a virtual edge; otherwise, GAMBIT creates a real edge.
The Shape Parameter specifies the shape of the conic arc edge. Its allowable values range from 0.01 to 0.99. The relationship between the Shape Parameter and the arc shape is as follows (see Figure 238).
Shape Parameter  Arc Shape 
0.01 ≤ ≤ 0.50  Elliptical 
= 0.50  Parabolic 
0.50 < ≤ 0.99  Hyperbolic 
To open the Create Conic Arc form (see below), click the Create Conic Arc command button on the Geometry/Edge subpad.
The Create Conic Arc form includes the following specifications.
Vertex:  
Start  specifies the vertex that constitutes the start endpoint of the edge. 
Shoulder  specifies the vertex that defines the apex of the conic edge. 
End  specifies the vertex that constitutes the end endpoint of the edge. 
Shape Parameter  specifies the shape parameter for the arc (see above). NOTE: GAMBIT displays the name of the shape corresponding to the currently specified Shape Parameter. 
Label  specifies a label for the new edge. (See Section 2.1.1.) 
The Create Real Fillet Arc operation (edge create fillet command) creates a fillet edge between two existing edges.
To create a fillet edge, you must specify the following parameters.
When you create a fillet edge, GAMBIT creates a circular arc edge between two existing edges that define the fillet. The defining edges may be straight or curved, but they must be coplanar. GAMBIT locates the fillet edge such that the circle that contains it is tangent to both edges. Furthermore, GAMBIT creates the fillet edge such that it constitutes the smaller of the two circular arcs that can be constructed between its endpoints (see Figure 239).
Figure 239: Fillet edge definition
When you create a fillet edge between two existing edges, you must specify a selection point (u value) for each edge. The selection point is a dimensionless length parameter that corresponds to the distance between the selection point and one of the endpoints on the selected edge.
If an edge pair provides more than one possible location for a fillet of a specified radius, the selection points determine the location at which GAMBIT constructs the fillet edge. The effect of the selection point location varies according to whether or not the defining edges intersect each other. The general rules that apply to the effect of the selection point location are as follows.
If a pair of edges does not intersect but does provide more than one possible location for a fillet, GAMBIT constructs the fillet edge nearest the selection point for one of the two edges. As an example, consider the two edges shown in Figure 240. In Figure 240(a), the selection points are both near the leftmost ends of the defining edges, therefore GAMBIT locates the fillet edge on the left. Similarly, in Figure 240(b), the selection points are near the rightmost ends of the defining edges, therefore GAMBIT locates the fillet edge on the right. In Figure 240(c), one of the selection points is near the left end of one edge, and the other selection point is near the right end of the other. In such cases, the final location of the fillet edge depends on the orientations and shapes of the defining edges.
When the edges that define the fillet intersect each other, the fillet location depends on the following two factors.
Figure 240: Fillet location—nonintersecting edges
Figure 241: Fillet location—intersecting edges
When you create a fillet edge, the location of the fillet depends, in part, on the fillet radius. Figure 242 shows the effect of fillet radius on the location of a fillet edge constructed between two curved edges. Note that both fillet edges shown in Figure 242 are located such that the circles that contain them are tangent to the defining edges at their points of intersection.
Figure 242: The effect of fillet radius on fillet edge location
If you specify a fillet radius that is either too small or too large to result in points of tangency between the defining edges, GAMBIT does not create the fillet edge.
When you create a fillet edge, GAMBIT allows you to specify that both of the defining edges are trimmed when the fillet edge is created. If you select the trimedges option, GAMBIT deletes two of the four edge segments that exist on either side of the fillet edge endpoints. Figure 243 shows the difference between trimmed and untrimmed edges when creating a fillet edge according to the specifications shown in Figure 239.
Figure 243: Fillet edge—effect of trimming edges
When you specify that the defining edges are to be trimmed, GAMBIT uses the locations of the selection points to determine which edge segments to retain. As a general rule, GAMBIT retains the edge segments that contain the selection points. Figure 244 shows the effect of edge trimming on two nonintersecting edges possessing shapes and orientations identical to those shown in Figure 240. Figure 245 shows the effect of edge trimming on two perpendicular intersecting edges identical to those shown in Figure 241.
Figure 244: Fillet edge trimming—nonintersecting edges
Figure 245: Fillet edge trimming—intersecting edges
To open the Create Real Fillet Arc form (see below), click the Create Real Fillet Arc command button on the Geometry/Edge subpad.
The Create Real Fillet Arc form includes the following specifications.
Edge 1  specifies one of two edges that define the fillet. 
Uval1  specifies the location of the selection point for Edge 1. 
Edge 2  specifies the second of two edges that define the fillet. 
Uval2  specifies the location of the selection point for Edge 2. 
Radius  specifies the fillet radius. 
Trim edges  trims the defining edges. 
Label  specifies a name for the new edge. (See Section 2.1.1.) 
The Create Edge from Vertices operation (edge create nurbs command) creates an edge the shape of which is defined by a set of vertices.
When you create an edge by means of the Create Edge from Vertices command, GAMBIT forms the edge in the shape of a general NURBS curve of degree n. A NURBS curve of degree n is a piecewise rational polynomial function wherein the numerator and denominator are nonperiodic Bsplines of degree n. By default, GAMBIT employs a value of n = 3 and applies natural boundary conditions at the endpoint vertices. That is, the NURBS curve is created such that its second derivative is zero at the endpoints.
To create a NURBS edge, you must specify the following parameters.
You can specify any combination of real and/or virtual vertices for the Create Edge from Vertices operation. The sequence in which you specify the vertices determines the shape of the edge. In addition, the first and last vertices specified determine whether the created edge is real or virtual. Specifically, if either the first or last specified vertex is a virtual vertex, GAMBIT creates a virtual edge; otherwise, GAMBIT creates a real edge.
GAMBIT provides two methods for constructing a NURBS edge.
Figure 246: NURBS curve methods
To open the Create Edge from Vertices form (see below), click the Create Edge from Vertices command button on the Geometry/Edge subpad.
The Create Edge from Vertices form includes the following specifications.
Vertices  specifies the vertices to be used in creation of the edge. 
Method:  
Interpolate  specifies that the edge passes through all vertices. 
Approximate  specifies that the edge passes near to all internal vertices to within the specified Tolerance value. 
Tolerance  specifies the maximum allowable distance between the NURBS curve and any of the internal vertices (default = 0.0). 
Label  specifies a label for the new edge. (See Section 2.1.1.) 
The Sweep Vertices operation (edge create translate command) creates edges by sweeping one or more real or nonreal vertices along a specified path. The command requires the following input parameters:
To create an edge by means of the Sweep Vertices operation, you must specify a set of one or more vertices to be swept. The set can consist of any combination of real and/or nonreal vertices. Each real vertex specified produces a real edge; each nonreal vertex produces a virtual edge.
If you specify a vector to define the sweep path, GAMBIT defines the path as a straight line possessing the magnitude and direction of the vector. The vector is defined by means of the Vector Definition form (see "Using the Vector Definition Form" in Section 2.1.4).
To open the Sweep Vertices form (see below), click the Sweep Vertices command button on the Geometry/Edge subpad.
The Sweep Vertices form includes the following specifications.
Vertices  specifies one or more real and/or nonreal vertices to be swept. (NOTE: GAMBIT creates a separate edge for each vertex.) 
Path:  
Edge  specifies that the path is described by the length, shape, orientation, and sense of an existing edge. 
Edge  specifies the edge to be used as the sweep path. 
Reverse  reverses the direction of the path relative to the sense of the specified edge. 
Vector  specifies that the path is described by a vector.
When you select the Vector option, GAMBIT displays a pushbutton titled Define. When you click the Define pushbutton, GAMBIT opens the Vector Definition form, which allows you to specify parameters that define the path vector. For instructions on using the Vector Definition form, see "Using the Vector Definition Form" in Section 2.1.4. 
Label  specifies a label for the new edge. (See Section 2.1.1) 
The Revolve Vertices operation (edge create revolve command) creates real circular arc edges or helixes by revolving existing real and/or nonreal vertices about a specified axis. The command requires the following input parameters.
When you create an edge by revolving a vertex, GAMBIT sweeps the vertex through the specified angle of revolution to create a circular arc edge (see Figure 247). (NOTE: If you revolve a nonreal vertex, GAMBIT makes a real, inplace copy of the nonreal vertex and revolves the real copy to create the edge.) The vertex specified for revolution (or real, inplace copy) constitutes the start endpoint of the created edge, and the edge sense points in the direction of revolution.
Figure 247: Revolve Vertices operation
You can specify any number of real and/or nonreal vertices for the Revolve Vertices operation. As noted above, if you specify a nonreal vertex, GAMBIT copies the virtual vertex to create a real vertex at the same location and revolves the real vertex to create a real edge. As a result, the Revolve Vertices command always creates a real edge regardless of the geometry type of the specified vertex.
To specify the axis of revolution, 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 revolution for the Revolve Vertices operation are identical to those described in "Rotating an Entity," in Section 2.1.4.
If you input a value for the Height specification on the Revolve Vertices form, GAMBIT creates the circular arc edge in the shape of a helix with the specified height. As an example of the effect of the Height specification, consider the arc edges shown in Figure 248.
Figure 248: Effect of Height specification
Both of the edges shown in the figure are created by revolving vertex A through an angle of 270° about an axis aligned with the y coordinate axis. Edges A and B represent the arc edges created using Height specifications of 0 and 10, respectively. Edge A is a circular arc edge that lies in the zx plane. Edge B is in the shape of a partial helix.
To open the Revolve Vertices form (see below), click the Revolve Vertices command button on the Geometry/Edge subpad.
The Revolve Vertices form includes the following specifications.
Vertices  specifies one or more real and/or virtual vertices to be revolved. 
Angle  specifies the angle through which the vertices are revolved. 
Axis:  includes two components:

Height  specifies the height for the creation of a helixshaped edge. 
Label  specifies a label for the new edge. (See Section 2.1.1) 
The Project Edges on Face operation (edge create project command) creates real edges that represent the projection of existing real or nonreal edges onto the surface of an existing face.
When you execute the Project Edges on Face command, GAMBIT creates a set of one or more real edges the shapes of which represent the projection of specified (projection) edge(s) onto the surface of a specified (target) face (see Figure 249). The shape of any edge created by the operation follows the contours of the target face.
Figure 249: Project Edges on Face operation
If the projection of an edge extends beyond the boundaries of the target face, GAMBIT truncates the created edge at the face boundaries. In addition, if the projection of an edge crosses the face boundaries more than once, GAMBIT creates multiple edges from the operation (see Figure 250).
Figure 250: Project Edges on Face—creation of multiple edges
The Project Edges on Face command includes the following specifications:
The projection edges and target face can represent any combination of real and/or nonreal entities. For example, it is possible to project a real edge onto a virtual face or a set of real and nonreal edges onto a real face. Regardless of the geometry types of the specified edges and face, however, the Project Edges on Face operation creates real edges on the surface of the target face.
GAMBIT provides two options for specifying the direction in which the edges are to be projected:
Figure 251 illustrates the effect of the direction option on the results of a simple projection operation involving a single edge. In this case, the projecttion edge is a circular arc edge aligned with the zx coordinate plane, and the target face is a square planar face tilted at an angle of 30° with respect to the zx coordinate plane.
Figure 251: Project Edges on Face—effect of direction options
If you select the Closest distance option, GAMBIT projects each point on the circular arc edge in a direction normal to the planar surface. If you select the Direction option and specify Y Negative as the projection direction (by means of the Vector Definition form), GAMBIT projects each point on the edge in the –y direction.
If you specify the Split face option when projecting a set of edges onto a face, GAMBIT uses the created edge(s) to split the target face. For example, if you project a curved edge onto a planar rectangular face as shown in Figure 252 and specify the Split face option, GAMBIT splits the target face and creates two virtual faces from the edgeproject operation. In this case, the projection of the edge extends beyond the face boundaries; therefore, the face is fully split to create two new faces.
Figure 252: Project Edges on Face—effect of Split face option
If the projection of an edge does not extend beyond the target face boundaries, the Split face option creates a single virtual face with a dangling edge (see Figure 253).
Figure 253: Project Edges on Face—effect of Split face option, dangling edge
To open the Project Edges on Face form (see below), click the Project Edges on Face command button on the Geometry/Face subpad.
The Project Edges on Face form includes the following specifications.
Edges  specifies the set of edges to be projected. 
Face  specifies the target face that constitutes the projection surface. 
Closest distance  specifies that GAMBIT projects each point on the projection edge(s) onto its closest point on the target face. 
Direction  specifies that GAMBIT projects each point on the projection edge(s) in a userspecified direction. When you select this option, GAMBIT activates a Define command button that opens the Vector Definition form. 
Split face  uses the created edge(s) to split the target face. 
Label  specifies a label for the new edge. (See Section 2.1.1.) 
The Connect/Disconnect Edges command button allows you to perform the following 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. 
The Connect Edges operation (edge connect command) connects sets of two or more edges. When you connect a set of edges, GAMBIT replaces the edges in the set with a single edge.
NOTE (1): If you connect two or more meshed edges and the numbers of mesh nodes on each edge are identical to each other, GAMBIT preserves the meshes when connecting the edges. 
NOTE (2): If any of the edges to be connected are meshlinked to other edges in the model, GAMBIT preserves the mesh link(s) and assigns it/them to the single edge that results from the connect operation. 
To connect edges, you must specify the following parameters:
The edges to be connected can be real or virtual, but they are subject to certain restrictions imposed by the connection type (see below).
GAMBIT allows the following types of edgeconnect operations:
The Real option allows you to connect coincident real edgesthat is, two or more real edges that possess identical orientations and the endpoint vertices of which are coincident to within a global tolerance value of 10^{6}. When you connect real edges and specify the Real option, GAMBIT deletes all but one of the specified edges and connects the remaining real edge to any and all faces to which the deleted edges were connected.
The Virtual (Forced) option allows you to connect real or virtual edges, regardless of their proximity to each other. When you connect edges and specify the Virtual (Forced) option, GAMBIT replaces the specified edges with a virtual edge. If a specified edge constitutes part of a face, GAMBIT overlays the face with a virtual face and shapes the virtual face according to the position of the new virtual edge. If the face is connected to a volume, GAMBIT overlays the volume with a virtual volume.
The Virtual (Tolerance) option allows you to specify that only those real and/or virtual edges that are near to each other to within a specified tolerance are connected. There are two ways to express the tolerance value:
If you specify the Virtual (Tolerance) option, you can also specify the TJunctions option. The TJunctions option allows the creation of Tjunctions during the edge connect operation (see "Specifying the TJunctions Option," below).
When you specify the Real and Virtual (Tolerance) option, GAMBIT performs the following two operations in sequence:
If you connect a set of edges using a Virtual(Forced), Virtual (Tolerance), or Real and Virtual (Tolerance) operation, you can determine the shape of the resulting edge by means of the Preserve first edge shape option. When you select the Preserve first edge shape option, the edge that results from the connect operation retains the shape of the first edge listed in the Edges list. If you do not select the Preserve first edge shape option when connecting the edges, the shape and location of the edge that results from the connect operation represents an average of the shapes and locations of the edges to be connected. (NOTE: GAMBIT does not allow you to specify the Preserve first edge shape option in conjunction with the TJunctions option (see below).)
When you employ the Virtual (Tolerance) or Real and Virtual (Tolerance) option, GAMBIT allows you to select the TJunctions option. If you specify the TJunctions option, GAMBIT performs virtual Tconnect operations where appropriate to connect edges the endpoints of which are near to the virtual edge to within a specified tolerance. (For a description of virtual Tconnect operations, see Appendix A of this guide.)
As an example of the use of the TJunctions option, consider the edges shown in Figure 254(a). If you specify the TJunctions option when performing a Virtual (Tolerance) or Real and Virtual (Tolerance) connection operation involving edge.1 and edge.2, GAMBIT splits edge.2 and creates a Tconnection at v_vertex.5 (see Figure 254(b)).
Figure 254: Connecting edges—TJunctions option
NOTE: If you select the TJunctions option, GAMBIT deactivates the Preserve first edge shape option. 
When you perform a Tconnection operation, GAMBIT allows you to specify the Preserve splitedge shape option. When you select the Preserve splitedge shape option, GAMBIT retains the shape of the edge to be split during the Tconnection operation.
As an example of the effect of the Preserve splitedge shape option, consider the two edges (edge.1 and edge.2) shown in Figure255(a).
Figure 255: Effect of the Preserve splitedge shape option
NOTE: The Preserve splitedge shape option takes precedence over the Preserve first edge shape option. 
To open the Connect Edges form (see below), click the Connect command button on the Geometry/Edge subpad.
The Connect Edges form includes the following specifications.
Edges  specifies the edges to be connected. 
All Pick 

Real  specifies that the edge that results from the connection of edges is a real edge. (NOTE: To obtain a real edge from the connection of two or more real edges, the specified edges must be coincident.) 
Virtual (Forced)  specifies the following characteristics for the edge that results from connection of edges:

Virtual (Tolerance)  specifies the following characteristics for the edge that results from connection of edges:

Real and Virtual (Tolerance)  specifies the following sequence of operations:

Tolerance  specifies the maximum allowable distance (absolute units) between edges to be connected. 
Shortest Edge %  specifies the maximum allowable distance (percent of shortest edge) between edges to be connected. 
Highlight shortest edge  highlights the shortest edge that exists in the current model. 
Preserve first edge shape  preserves the shape of the first edge listed in the Edges list when performing the connect operation. 
TJunctions  specifies the creation of Tjunctions where possible. (NOTE: If you select the TJunctions option, GAMBIT deactivates the Preserve first edge shape option.) 
Vertices  (All or Pick) specifies vertices subject to the TJunctions option. 
Preserve splitedge shape  preserves the shape of the edge to be split during TJunctions operations. 
The Disconnect About Real Edge operation (edge disconnect command) disconnects topological entities that share a common real edge.
When you disconnect faces or volumes about a common real edge, GAMBIT creates new edges for all but one of the entities to which the specified edge is connected. For example, if the specified edge is shared by three faces, GAMBIT creates two new edges that are coincident with the specified edge and connects them to two of the three faces. The original edge is connected to the remaining face.
GAMBIT provides the following options with respect to the treatment of endpoint vertices for the disconnected edge:
Option  Description 
Edge + Vertices  GAMBIT disconnects the specified edge and its endpoint vertices. As a result, GAMBIT creates two new endpoint vertices for each new edge. 
Edge Only  GAMBIT disconnects the edge but not its endpoint vertices. Each new edge created in the disconnection process shares the endpoint vertices of the specified edge. 
Edge + Select Vertex  GAMBIT disconnects the edge and one of its two endpoint vertices (specified by the user). The other endpoint vertex is shared between all new edges. 
As an example of the difference between the options described above, consider the configuration shown in Figure 256, in which two faces are connected by means of a common edge (edge.4) the endpoint vertices of which (vertex.3 and vertex.4) are also common to both faces.
Figure 256: Two faces sharing a common edge
If you disconnect the faces about edge.4, GAMBIT creates a new edge that is coincident with edge.4 and connects it to one of the two faces—for example, face.2. The original edge (edge.4) remains connected to the other face (face.1).
The manner in which GAMBIT treats the endpoint vertices varies according to the option type as follows.
Option  Description 
Edge + Vertices  GAMBIT disconnects vertex.3 and vertex.4 and designates the vertices that result from the disconnection as the endpoints of the new edge. 
Edge Only  GAMBIT does not disconnect vertex.3 and vertex.4. The new edge shares endpoint vertices with edge.4; that is, vertex.3 and vertex.4 are common to both edges. 
Edge + Select Vertex  GAMBIT disconnects only one of the endpoint vertices of edge.4. The other vertex (vertex.3 or vertex.4) constitutes an endpoint of both the specified edge and the new edge. 
To open the Disconnect About Real Edge form (see below), click the Disconnect About Real Edge command button on the Geometry/Edge subpad.
The Disconnect About Real Edge form includes the following specifications.
Edge  specifies the edge about which geometry is to be disconnected. 
Method:  
Edge + Vertices  specifies that the endpoint vertices of the specified edge are to be disconnected along with the edge. 
Edge Only  specifies that the endpoint vertices of the specified edge are to remain connected when the edge is disconnected. 
Edge + Select Vertex  specifies that only one of the two endpoint vertices for the specified edge is to be disconnected. 
Vertex  specifies the vertex that is to be disconnected in conjunction with the specified edge. 
The Modify Edge 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.
The Modify Edge Color operation (edge modify command) changes the displayed color of the geometry and/or mesh nodes associated with one or more edges.
To open the Modify Edge Color form (see below), click the Modify Color command button on the Geometry/Edge subpad.
The Modify Edge Color form includes the following specifications.
Edges  specifies one or more edges for which the color is to be changed. 
Color:  
Geometry  specifies modifying the color of the specified edge(s). 
Mesh  specifies modifying the color of the mesh node(s) associated with the specified edge(s).. 
For specific instructions on setting the Geometry or Mesh colors, see Section 2.2.4.
The Modify Edge Label operation (edge modify command) changes the label associated with any edge.
To open the Modify Edge Label form (see below), click the Modify Label command button on the Geometry/Edge subpad.
The Modify Edge Label form includes the following specifications.
Edge  specifies the edge to be modified. 
Label  specifies a new label for the edge. (See Section 2.1.1). 
The Move/Copy/Align Edges command button allows you to perform two operations.
Symbol  Operation  Description 
Move/Copy Edges  Moves and copies edges  
Align Edges  Aligns edges and connected geometry with existing topological entities 
The following sections describe the procedures and specifications required to execute the operations listed above.
The Move/Copy Edges operation (edge copy, edge move, edge cmove, edge reflect, edge creflect, edge scale, and edge cscale commands) repositions and/or reorients one or more edges or creates copies of edges. 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.
For a complete description of the specifications available on the Move/Copy Edges form, see "Using Move/Copy Forms" in Section 2.1.4.
The Align Edges operation (edge align command) repositions a set of one or more edges with respect to a set of translation and rotation vertices. (NOTE: You cannot planealign an edge, because edges are onedimensional entities.) For a general description of the procedure and specifications required to align an entity, see "Aligning an Entity" in Section 2.1.4, above.
To open the Align Edges form (see below), click the Align command button on the Geometry/Edge subpad.
For a complete description of the specifications available on the Align Edges form, see "Using Align Forms" in Section 2.1.4.
The Split/Merge Edges command button allows you to perform the following operations.
Symbol  Command  Description 
Split Edge  Splits an existing edge into two real or virtual edges  
Merge Edges  Merges two or more existing edges into a real or virtual edge 
The following sections describe the procedures and specifications required to execute the operations listed above.
The Split Edge (edge split and edge split virtual commands) splits an existing edge into two real or virtual edges. (NOTE: If you split an edge that is linked to one or more edges, GAMBIT splits every edge in the set of linked edges in addition to the specified edge.)
NOTE: GAMBIT allows you to split edges that are involved in the definitions of existing size functions and boundary layers. The effect of such split operations depends on the role of the target edge (the edge to be split) in the sizefunction or boundarylayer definition.
If you split an edge that serves as a source or attachment entity for a size function and one of the edges resulting from the split operation retains the label of the original edge, GAMBIT preserves the size function and assigns it to the edge that retains the original label. If you split a faceboundary edge that serves as an attachment entity for a 2D boundary layer, GAMBIT retains the boundary layer definition and applies it to both edges resulting from the split operation. If you split a face or volumeboundary edge on which a 2D or 3D boundary layer is propagated, GAMBIT attempts to retain the boundary layer when splitting the edge. If the split point is located outside the boundary layer, GAMBIT preserves the boundary layer; otherwise, the boundary layer is deleted. 
The Split Edge command includes the following input parameters:
GAMBIT allows you to split real or virtual edges but places the following restrictions on the type of edges that can be created from the split:
There are three types of edge split operations:
NOTE: GAMBIT does not allow you to employ the Real disconnected option when splitting edges that are associated with highertopology face or volume entities. 
When you split an edge, you must specify the location at which the edge is to be split. To do so, you must designate a split tool—that is, the means of locating the split point. There are three types of split tools:
If you split a real or virtual edge using a point as the split tool, you must specify a U Value parameter that identifies the location of the point on the edge. The U Value parameter represents the fraction of total edge length and is equivalent to the u value used when creating a vertex on an edge. (For a detailed description of the u value, see "Create Vertex on Edge," in Section 2.2.1.)
When you specify the Point option and pick the edge from the graphics window using the mouse, GAMBIT highlights the edge and shows the location of the split point. You can slide the split point along the edge until you release either the Shift key or the left mouse buttonat which time GAMBIT fixes the position of the split point. To change the position of the split point, either repick (Shiftmiddleclick) the edge and move the point to another location, or input the desired u value in the U Value text box on the Split Edge form.
If you split an edge using the Vertex option, you must specify an existing vertex that identifies the location of the split point. The rules governing the type of vertex that can be used to split an edge are as follows:
If you specify the Virtual connected splittype option (see above) and specify a vertex as the split tool, you can specify a Tolerance value that determines whether GAMBIT performs the split operation (default = 10^{6}). If the splittool vertex is coincident with the edge or near to the edge within the specified Tolerance value, GAMBIT performs the split operation. The final shape and location of the split edge is determined by the Splitedge Position (see below).
Specifying the Splitedge Position
When you split an edge with a splittool vertex that is not coincident with the edge, GAMBIT allows you to determine the final configuration of the edge shape and vertex location by means of the Splitedge Position specification. The Splitedge Position specification includes three options (see Figure 257):
Figure 257: Splitedge Position options
The Edge option allows you to split an edge at a location defined by the point(s) of intersection (or closest approach) between the specified (target) edge and an edge that serves as a split tool. If the target edge intersects or approaches the splittool edge at more than one location, GAMBIT splits the target edge at each location.
GAMBIT provides two suboptions for the Edge splittool option:
The Bidirectional suboption splits both the target edge and the splittool edge at their point(s) of intersection or closest approach. The target edge and splittool edge are joined together at the split location. That is, the vertices created at the edge split locations are connected after the split operation is complete.
Specifying a Tolerance Value
If you select the Edge splittool option, GAMBIT performs the split operation at points of near intersection between the splittool edge and the target edge. For the purposes of the edgesplit operation, edges are considered to nearly intersect if they approach each other to within the Tolerance value specified on the Split Edge form (default = 10^{6}).
To open the Split Edge form (see below), click the Split command button on the Geometry/Edge subpad.
The Split Edge form includes the following specifications.
Edge 
specifies the edge to be split 
Type 

Real connected Real disconnected Virtual connected 
specifies the type of edges that result from the edgesplit operation. 
Split With 

Point Vertex Edge 
specifies the general nature of the split tool. 
The lower section of the Split Edge form allows you to specify parameters related to the Split With option selected (Point, Vertex, or Edge).
U Value  specifies the u value position parameter. 
Coordinate Sys.  specifies the coordinate system with respect to which the splittool point is specified. (See Section 2.1.3.) 
Type  
Cartesian Cylindrical Spherical 
specifies the type of coordinate parameters to be used in locating the split point. 
GlobalLocal  Specifies the location of the point with respect to either the Global or Local system. 
When you specify the Split With:Vertex option, the middle section of the Split Edge form appears as shown below.
Vertex 
specifies the vertex to be used as the split tool. 
Tolerance  (Virtual connected split operations only) specifies that the vertex is to be used as a splittool if it is located near the target edge to within the specified tolerance value (default = 10^{6}). 
Splitedge Position  (Virtual connected split operations only) 
Interpolate  shapes split edges such that the connecting vertex is located between the original edge and splittool vertex. 
Preserve vertex location  shapes split edges such that the splittool vertex is retained as the location of the connecting vertex between split edges. 
Preserve edge shape  retains the edge shape and projects the splittool vertex onto the edge to be split. 
When you specify the Split With:Edge option, the middle section of the Split Edge form appears as shown below.
Edge  specifies the edge to be used as the split tool. 
Retain  specifies that the splittool edge is retained upon completion of the edgesplit operation. 
Bidirectional  specifies that the splittool edge is retained and is split at the points of intersection upon completion of the edgesplit operation. 
Tolerance  specifies that a given location is considered a point of intersection if the target and splittool edge approach to within the specified tolerance value (default = 10^{6}). 
The Merge Edges operation (edge merge command) merges two or more real and/or virtual edges into a real or virtual edge. (NOTE: If you merge edges that possess identical boundaryzone type specifications, GAMBIT assigns the specification to the edge that results from the merge operation.)
To merge edges by means of the Merge Edges command, you must specify the following parameters:
GAMBIT applies the following rules with respect to the set of edges to be merged (see Figure 258):
Figure 258: GAMBIT edgemerging rules
NOTE: If you merge a set of edges one of which serves as a source or attachment entity for a size function, and the edge that results from the merge operation retains the label of the source or attachment edge, GAMBIT preserves the size function and assigns it to the new edge. 
When you merge edges, you must specify the merge type. There are two types of edgemerging operations:
When you specify a Virtual (Tolerance) merge, GAMBIT attempts to create a virtual edge if all edges in the set meet specified tolerance criteria.
There are two types of edgemerging tolerance criteria:
The Min. Angle criterion is based on the internal angle between edge pairs. When you specify the Virtual (Tolerance) option, GAMBIT includes in the merge operation only those edge pairs the internal angles of which are greater than the specified angle.
To open the Merge Edges form (see below), click the Merge command button on the Geometry/Edge subpad.
The Merge Edges form includes the following specifications.
Edges  specifies the set of edges to be merged. 
All Pick 
(Virtual (Tolerance) option only)

Type:  
Real and Virtual (Forced)  specifies that the edges in the set are to be merged regardless of their respective lengths or orientations to each other. 
Virtual (Tolerance)  specifies that the edges in the set are to be merged only if all edges and orientations meet the tolerance criteria. 
Max. Edge Length  specifies the maximum edge length tolerance criterion. 
Min. Angle  specifies the minimum angle tolerance criterion (in degrees). 
The Smooth/Convert Edges command button allows you to perform the following operations.
Symbol  Command  Description 
Smooth Real Edges  Smoothes real edges to repair bad geometry and reduce complexity  
Convert Edges (Nonreal to Real)  Converts nonreal edges to real edges 
The following sections describe the procedures and specifications required to execute the operations listed above.
The Smooth Real Edges operation (edge smooth command) automatically repairs edge geometry conditions that might cause problems for the ACIS modeler.
GAMBIT real geometry operations employ ACIS modeling techniques. ACIS modeling algorithms require a high degree of precision and accuracy in the geometric data that describe the model. Such precision and accuracy manifests itself in the form of tight distance tolerances and completeness of connectivity information.
In most cases, model geometry data generated from within GAMBIT automatically meet the stringent integrity standards required by the ACIS modeler. However, a few GAMBIT operations sometimes produce geometry that fails to meet the ACIS standards. Geometry imported to GAMBIT from outside sources might not meet such standards, either, due to any of the following factors:
In addition to these two options, GAMBIT allows you to specify a Tolerance option. The Tolerance option determines the maximum allowable distance that the spline control points can be moved during the smooth operation.
NOTE (1): The edgesmooth operation should be performed as soon as possible after the specified edges are created or imported. Doing so reduces the chances of the migration of any discontinuities into other geometry and simplifies the task of smoothing.
NOTE (2): The edgesmooth operation should involve as many edges at one time as possible, because the smoothing algorithm takes advantage of fact that one geometrical entity can support multiple topological entities. 
When you select the Replace bad geometry option, GAMBIT detects any edges that possess bad geometry (including geometry with G1 and C1 discontinuities) and attempts to reconstruct the edges to repair the geometry.
When you select the Reduce complexity option, GAMBIT attempts to reduce the number of control points in the spline definition of the underlying curve. (NOTE: The Reduce complexity option applies only to edges that are associated with a spline definition.)
When you select the Replace bad geometry or Reduce complexity option, you can also specify a Tolerance option. The Tolerance option determines the maximum allowable distance that the spline control points can be moved.
GAMBIT provides two Tolerance options:
To open the Smooth Real Edges form (see below), click the Smooth Real Edges command button on the Geometry/Edge subpad.
The Smooth Real Edges form includes the following specifications.
Edges  specifies the edges to be smoothed. 
All Pick 

Replace bad geometry  attempts to reconstruct the specified edges to replace bad geometry. 
Reduce complexity  attempts to reduce the number of control points in the spline definition of the underlying curve(s). (NOTE: This option applies only to edges that are associated with a spline definition.) 
Tolerance  specifies the maximum distance that any of the spline control points can be moved. GAMBIT provides two Tolerance options:

The Convert Edges (Nonreal to Real) operation (edge convert command) converts one or more nonreal (faceted and/or virtual) edges to real edges. The conversion process preserves both the topology and any existing mesh(es) associated with the converted edge(s). In addition, all nonreal vertices associated with the edge(s) are converted to real vertices.
NOTE: To determine the shape of the converted edge, GAMBIT facets the edge using a userspecified number of points and fits the points with a spline. To specify the number of points used in the fitting procedure, open the Edit Defaults form and modify the variable "VIRTUAL_SAMPLING_POINTS" (see Chapter 4 of the GAMBIT User’s Guide). 
To open the Convert Edges (Nonreal to Real) form (see below), click the Convert command button on the Geometry/Edge subpad.
The Convert Edges (Nonreal to Real) form includes the following specifications.
Edges  specifies which nonreal edges are to be converted to real edges. 
All Pick 

The Summarize/Check/Query Edges 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.
The Summarize Edges operation (edge summarize command) displays edge summary information in the Transcript window.
To open the Summarize Edges form (see below), click the Summarize command button on the Geometry/Edge subpad.
The Summarize Edges form includes the following specifications.
Edges  specifies the edges for which information is to be summarized in the Transcript window. 
All Pick 

The Check Edges operation (edge check command) assesses the topological and/or geometrical validity of edges in the model and summarizes the results in the Transcript window.
When you execute the Check Edges command, GAMBIT checks the model to determine its validity with respect to either or both of the following types of characteristics:
Topological validity is an assessment of the underlying organization of the modelfor 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 virtualgeometry, guesthost relationship.
For a given edge, the Check Edges topology check operation examines the model to ensure that it meets the following criteria:
NOTE (1): Failure of the topology check for any edge 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. 
NOTE (2): GAMBIT can automatically check the validity of all input and output (created) entities for any geometry operation and display warning or error messages in the Transcript window for any entity that fails the check(s). The automaticchecking behavior is specified by means of the GEOMETRY.GENERAL.CHECK_LEVEL default variable, which can be set to any of the following values.

Geometrical validity is an assessment of the model with respect to proximity and shape characteristicssuch as the distances between connected edges and/or the mathematical continuity of model curves and surfaces. The Check Edges geometry check criteria are as follows:
NOTE: Failure of the geometry check for a model edge does not necessarily constitute a serious problem for the model as a whole. It is sometimes possible to repair geometry errors for edges that belong to faces for which a Heal Real Faces (see Section 2.4.7) or Heal Real Volumes (see Section 2.5.8) operation is attempted. 
To open the Check Edges form (see below), click the Check command button on the Geometry/Edge subpad.
The Check Edges form includes the following specifications.
Edges  specifies the edges to be included in the checking operations. 
All Pick 

Check Topology  specifies a topology check on the selected edges. 
Check Geometry  specifies a geomtery check on the selected edges. 
The Query Edges operation (no corresponding commandline command) allows you to identify the locations and/or labels of individual edges or subsets of edges in the model. Its use is similar to that of the Query Vertices command (see "Query Vertices" in Section 2.2.7, above).
To open the Query Edges form (see below), click the Query command button on the Geometry/Edge subpad.
For a general description of the Query Edges form, see "Query Vertices" in Section 2.2.7, above.
The Total Entities operation (list totals 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.
For a description of the options available on the Total Entities form, see "Total Entities," in Section 2.2.7.
The Delete Edges operation (edge delete command) deletes one or more edges from the model subject to the following restrictions:
By default, when you delete an edge, GAMBIT deletes the vertices that constitute the endpoints of the edge. To retain the endpoint vertices when the edge is deleted, unselect the Lower Geometry option at the bottom of the Delete Edges form.
When you delete an edge that constitutes a host entity for one or more virtual vertices, GAMBIT deletes the virtual vertices when it deletes the edge.
To open the Delete Edges form (see below), click the Delete command button on the Geometry/Edge subpad.
The Delete Edges form includes the following specifications.
Edges  specifies one or more edges to be deleted. 
All Pick 

Lower Geometry  specifies that all vertices that constitute endpoints of the specified edges are deleted. 