2. CREATING THE GEOMETRY

When you click the Geometry command button on the Operation toolpad, GAMBIT opens the Geometry subpad. The Geometry subpad contains command buttons that allow you to create, move, copy, modify, summarize, and delete vertices, edges, faces, and volumes. The Geometry subpad also contains a command button that allows you to perform operations involving groups of topological entities.

The symbols associated with each of the Geometry subpad command sets are as follows.

The following sections of this chapter describe general operations related to building a GAMBIT model as well as the commands necessary to create and modify the topological entities listed above.

2.1 General Operations

2.1.1 Labeling Entities

Each of the GAMBIT modeling forms that allow you to create a new entity also allow you to specify a label for the entity. For example, if you create a vertex using the Create Real Vertex form (Figure 2-1), you can specify a label for the vertex by entering a name in the Label text box at the bottom of the form.

Figure 2-1: Example Create Real Vertex form

If you create an entity or coordinate system without specifying a label, GAMBIT automatically assigns a label to the entity. The automatically assigned label consists of a name representing the entity type followed by a decimal point and an integer-for example, volume.6. Automatically assigned labels for virtual and faceted entities are preceded by the characters "v_" and "f_"-for example, v_volume.6 and f_edge.12.

GAMBIT uses the following names for automatically labeled entities and coordinate systems.

The integer that GAMBIT assigns to automatically labeled entity names is equal to n+1, where n is the highest integer associated with any currently existing entity of the same type. The value of the assigned integer is independent of whether or not the entity is real or virtual.

The following examples summarize the general rules that GAMBIT uses for automatically labeling new entities.

• If you create a real vertex in a model that already contains vertices labeled vertex.1, vertex.2, and vertex.3, the new vertex is named vertex.4.
• If you create real vertices vertex.1, vertex.2, and vertex.3, then delete vertex.3-so that the model only contains vertex.1 and vertex.2-the next automatically labeled real vertex is named vertex.3.
• If you create real vertices vertex.1, vertex.2, and vertex.3, then delete vertex.2-so that the model only contains vertex.1 and vertex.3, the next automatically labeled real vertex is named vertex.4.

2.1.2 Specifying Entities

Specifying Individual Entities

Many of the modeling forms require you to specify individual entities-such as vertices, edges, or faces-to which to apply the operations specified on the form. When a form requires you to specify one or more individual entities, it contains a list box titled with the entity type. For example, the Create Real Vertex form (see Figure 2-1) requires you to specify the coordinate system with respect to which the vertex is to be positioned; therefore, it contains a list box, titled Coordinate Sys.

Unless otherwise noted, you can specify an individual entity in one of three ways:

• Input the name of the entity in the list box.
• Click the pick-list button at the right side of the list box and select the entity by means of the pick-list form.
• Pick the entity from the model as displayed in the graphics window.

Specifying Multiple Entities

On some forms, GAMBIT provides a single list box for the specification of more than one entity. For example, on the Connect Faces form, GAMBIT provides only one list box for the specification of both faces to be connected. When GAMBIT provides only one list box for the specification of multiple entities, you can specify the entities in one of three ways:

• Input the first entity name, press Enter; and clear the list box. Input the second entity name and press Enter again.
• Click the pick-list button located at the right side of the list box and select the entities by means of the pick-list form.
• Pick a vertex or edge associated with the first entity as displayed in the graphics window and Shift-right-click anywhere else in the graphics window to accept the selection. Then repeat the procedure for the second entity.

NOTE: To select entities that share a common lower-topology entity, pick the lower-topology entity multiple times. For example, to pick three faces that share a common edge, pick the edge three times.

2.1.3 Working with Coordinate Systems

Some of the GAMBIT modeling forms require you to specify a location in space relative to a specified coordinate system. For example, the Create Real Vertex form shown in Figure 2-1 requires you to specify the three coordinates describing the point at which the vertex is to be created.

You can specify point coordinates with respect to either a global or local coordinate system. GAMBIT's global coordinate system is named c_sys.1, and it cannot be deleted. As a result, it is always available for the specification of coordinates. To specify the coordinates of a point relative to a local coordinate system, you must first create the local system using the procedures outlined in Section 5.1.2 of this guide.

To specify the location of a point, you must specify the following information:

• The reference coordinate system (global or local)
• Three coordinate parameters that describe the point relative to the specified reference system

Specifying Reference Coordinate Systems

You can specify the reference coordinate system in one of three ways:

• Input the name of the coordinate system in the Coordinate Sys list box.
• Click the pick-list button located at the right side of the Coordinate Sys list box and select the system from the coordinate-system pick list.
• Pick the coordinate system (on one of its axes) in the graphics window.

Specifying Coordinate Parameters

To specify a point, you must input three parameters that define its location in space. GAMBIT allows you to specify the three parameters in terms of Cartesian, cylindrical, or spherical coordinates-regardless of the reference coordinate system type. For example, you can specify parameters in terms of spherical coordinates referenced to c_sys.1, which is defined as Cartesian, or in terms of Cartesian coordinates for any local system defined as cylindrical. GAMBIT modifies the titles on the Global and Local text boxes according to the specified location coordinate Type.

The required input parameters for each of the three types of coordinate systems are as follows.

The angle parameters, and , must be specified in degrees. They are defined such that vectors are coincident with the x, y, and z axes of a Cartesian coordinate system when and , have the following values.

When you input values for the coordinate parameters into the Global text boxes on any form, GAMBIT automatically updates the Local text box parameters to reflect the location definition relative to the local coordinate system. Likewise, when you input values into the Local text boxes, GAMBIT updates the Global text box parameters.

2.1.4 Moving, Copying and Aligning Entities

You can change the position and/or orientation of an entity in one of two ways:

• Move or copy the entity, by means of a Move/Copy form
• Align the entity, by means of an Align form

When you move an entity, GAMBIT changes its position and/or orientation relative to a specified reference object. The reference object can be a coordinate system, an axis around which the entity is to be rotated, or a plane relative to which the entity is to be reflected.

When you copy an entity, GAMBIT creates a duplicate of the entity and locates it according to the position and orientation specified on the Move/Copy form. Each copy includes all lower topology associated with the "parent" entity. For example, if you create a single copy of an edge, GAMBIT duplicates the edge and the pair of vertices that constitute its endpoints. If you copy an edge that constitutes part of a face or volume, GAMBIT duplicates only the edge and its endpoint vertices and does not duplicate the face or volume of which it is a component.

When you align an entity, GAMBIT changes its position and/or orientation relative to vertices already existing in the model. The GAMBIT alignment procedure constitutes a convenient way to make vertices, edges, faces, or volumes coincide with each other.

Moving an Entity

GAMBIT provides the following options with respect to moving an entity:

• Translate—moves the entity by a specified amount relative to its current position
• Rotate—rotates the entity about a specified axis
• Reflect—reflects the entity relative to a specified reflection plane
• Scale—enlarges or reduces the size of an entity according to a specified scaling factor

Each option is accessible by means of a Move/Copy form, such as that shown in Figure 2-2.

Figure 2-2: Example Move/Copy form

The following sections constitute a general description of each of the four options listed above.

Translating an Entity

When you translate an entity (see Figure 2-3), GAMBIT repositions the entity but does not change its orientation with respect to the reference coordinate system.

Figure 2-3: Example Move/Copy Volumes,Translate operation

To translate an entity, you must specify the following information:

• The reference coordinate system
• The translation parameters that define the new position of the entity relative to its current position

Rotating an Entity

When you rotate an entity (see Figure 2-4), GAMBIT repositions and reorients the entity by rotating its vertices and edges about a specified axis.

Figure 2-4: Example Move/Copy Volumes, Rotate operation

To rotate an entity, you must specify the following information:

• The axis around which the entity is to be rotated
• The angle of rotation

Specifying the Axis of Rotation

To rotate an entity, you must specify a vector that defines the axis of rotation. For the purposes of defining an axis of rotation, the magnitude of the vector is unimportant. The direction of the vector, however, defines the direction of rotation that is associated with positive values of the rotational angle. The vector is defined as positive in the direction from the start endpoint to the end endpoint.

You can specify the rotational axis vector in any of the following ways:

• Specify a coordinate system axis
• Specify any two existing vertices
• Specify the locations of any two points in space
• Specify any existing edge, the endpoints of which constitute the endpoints of the vector

GAMBIT constructs the vector according to the following conventions:

• If you specify a coordinate system axis, GAMBIT defines the rotational axis vector as a unit vector pointing in the direction of the axis.
• If you specify two existing vertices as the endpoints, GAMBIT constructs the vector from the Start vertex to the End vertex.
• If you specify two points as vector endpoints, GAMBIT constructs the vector from Point 1 to Point 2.
• If you specify an existing edge to define the vector, GAMBIT constructs the vector from the edge start vertex to the edge end vertex.

Each method listed above employs the Vector Definition form as means of defining the axis of rotation (see "Using the Vector Definition Form", below). To open the Vector Definition form, click the Axis Define command button on the Move/Copy form. (NOTE: When you select the Rotate option, the Axis Define command button appears in the middle section of the Move/Copy form.)

Reflecting an Entity

When you reflect an entity (see Figure 2-5), GAMBIT repositions the entity so that its vertices are equidistant from but on opposite sides of a specified reflection plane.

Figure 2-5: Example Move/Copy Volumes: Reflect operation

To reflect an entity, you must define the plane of reflection. To define the plane of reflection, you must specify a vector normal to the plane.

According to GAMBIT conventions, the start endpoint of the normal vector lies in the plane and, therefore, defines the location of the plane. The end endpoint determines the direction of the vector and, therefore, the orientation of the plane.

To specify the endpoints of the normal vector that defines the plane of reflection, you must employ the same procedure used to specify the axis of rotation by means of the Vector Definition form. (See "Using the Vector Definition Form," below.)

Scaling an Entity

When you scale an entity (see Figure 2-6), GAMBIT changes the size of the entity according to a specified scaling factor. If you specify translation parameters in addition to a scaling factor, GAMBIT also repositions the scaled entity.

Figure 2-6: Scaling of a rectangular brick

To scale an entity, you must specify the following information:

• Reference point
• Scaling factor

The reference point serves as the center projection point for the scaling operation. The scaling factor specifies the magnitude of the change in entity size.

NOTE: If you specify extreme values for the scaling factor, the scaling operation may produce invalid geometry.

• If you specify very large scaling factors, the scaled geometry may contain gaps between entities that are coincident with tolerance in the unscaled geometry.
• If you specify very small scaling factors, the scaled geometry may be smaller than the minimum allowable value of 10^-5.

Projecting the Geometry

When you scale an entity, GAMBIT projects each point associated with entity along a ray drawn from the reference point. For example, when GAMBIT scales a face such as that shown in Figure 2-7, it projects each point associated with the face, including its edges and vertices, away from the reference point.

Figure 2-7: GAMBIT face scaling operation

Specifying the Reference Point

To specify the reference point, you must specify a reference coordinate system (Global or Local) and three spatial coordinates that define the location of the reference point. If any point on the entity to be scaled is coincident with the reference point, the point does not change position as a result of the scaling operation. For example, in the scaling operation illustrated in Figure 2-6, one corner vertex of the rectangular brick volume to be scaled is exactly coincident with the reference point. As a result, the vertex itself does not change position when the brick is scaled.

If none of the vertices associated with the entity are coincident with the reference point, the entire entity is translated during the scaling operation. For example, if the rectangular brick shown in Figure 2-6 is initially offset from the reference point, then all of the vertices, edges, and faces associated with the brick are shifted when the brick is scaled (see Figure 2-8). As a result, the entire brick moves away from the reference point.

Figure 2-8: Scaling of a brick not coincident with the reference point

Moving Lower Topology

When you move an entity, GAMBIT also moves all lower topology associated with the entity. For example, if you move a rectangular brick volume using the Move/Copy Volumes form, GAMBIT translates, rotates, reflects, or scales all vertices, edges, and faces associated with the brick.

Moving Higher Topology and Connected Geometry

To move an entity that is connected to geometry of equal or higher topology, you must select the Connected Geometry option. When you select the Connected Geometry option and move an entity, GAMBIT moves all geometry of equal and higher topology geometry that is associated with the entity. For example, if you select the Connected Geometry option when attempting to move a vertex that constitutes one corner of a rectangular brick volume, GAMBIT moves the entire volume according to the specifications on the Move/Copy Vertices form.

Copying Mesh Information

• Copy mesh linked
• Copy mesh unlinked

Using Move/Copy Forms

Move/Copy forms allow you to reposition, reorient, and/or create copies of vertices, edges, faces, volumes, or groups. Each type of entity is associated with its own Move/Copy form, but all Move/Copy forms are identical with respect to the types of specifications available on the form. Move/Copy forms differ from each other only with respect to the type of entity being moved or copied.

To open any Move/Copy form, click the Move/Copy command button on the Geometry subpad specific to the entity being moved or copied. For example, to open the Move/Copy Vertices form (Figure 2-9), click the Move/Copy command button on the Geometry/Vertex subpad.

Figure 2-9: Example Move/Copy form

All Move/Copy forms include the following specifications.

The middle section of the Move/Copy form varies according to the type of operation selected. The following sections describe the specifications available for each operation.

Translation Specifications

When you specify the Translate operation, the middle section of the Move/Copy form appears as shown in Figure 2-9, above. Translate specifications are as follows.

Rotation Specifications

When you specify the Rotate operation, the middle section of the Move/Copy form appears as shown in Figure 2-10.

Figure 2-10: Move/Copyform, Rotate specifications

Rotate specifications are as follows.

Reflection Specifications

When you specify the Reflect operation, the middle section of the Move/Copy Vertices form appears as shown in Figure 2-11.

Figure 2-11: Move/Copy form, Reflect options

Reflect specifications are as follows.

Scaling Specifications

When you specify the Scale operation, the middle section of the Move/Copy Vertices form appears as shown in Figure 2-12.

Figure 2-12: Move/Copy form, Scale options

Scale specifications are as follows.

Using the Vector Definition Form

The Vector Definition form (see below) allows you to define a vector for use in GAMBIT operations such as the specification of axes of rotation or model orientation (for example, see "Orient Model" in Section 3.4.2 of the GAMBIT User's Guide). To define a vector, you must specify information regarding its magnitude and direction, as well as the location of its origin. GAMBIT provides several options for specifying such information.

The Vector Definition form includes the following specifications.

Active Coordinate System Vector	displays the coordinates of the origin (Start) and tip (End) for the current vector definition. (NOTE: The Start and End locations are always defined in terms of the active coordinate system.)
Magnitude	specifies the magnitude of the vector. (NOTE: If you input a negative value for the Magnitude parameter, GAMBIT reverses the direction of the vector relative to its Method-option definition but does not change the location of the vector origin.)
Method:	---------------------------------------------
Coord. Sys. Axis Edge 2 Points 2 Vertices Screen View	specifies the method to be used for specifying the vector endpoints. The available options are as follows: Coord. Sys. Axis—defines the vector with respect to one of the coordinate axes Edge—defines the vector by means of the endpoints of an existing edge 2 Vertices—defines the vector by means of two existing vertices 2 Points—defines the vector by means of two specified locations (points) in space Screen View—defines the vector relative to the model orientation currently displayed in the graphics window

The specifications available in the lower section of the Vector Definition form vary according to Method option. The following subsections describe specifications associated with each of the options listed above.

Specifying a Vector Defined by a Coordinate System Axis

When you select the Coord. Sys. Axis option, GAMBIT defines the vector with respect to a coordinate axis. To define the vector, you must specify the following information:

• The coordinate system to be used in defining the vector
• The axis and direction that defines the vector

For this option, the lower portion of the Vector Definition form appears as shown above and includes the following specifications.

Coordinate Sys.

specifies the reference coordinate system for the vector.

Direction:

contains radio buttons that allow you to specify the axis and direction to be used in the vector definition. The available options are as follows: X—Positive or Negative Y—Positive or Negative Z—Positive or Negative For example, if you specify c_sys.1 in the Coordinate Sys. list box and select the Z Negative orientation option, GAMBIT defines a vector that points in the negative direction along the z axis of c_sys.1 with an origin at the origin of c_sys.1.

Specifying a Vector Defined by a Model Edge

When you select the Edge option, GAMBIT defines the vector by means of the endpoint vertices of an existing edge. For this option, the lower portion of the Vector Definition form appears as shown below and includes the following specification.

Figure 2-13: Vector Definition form—Edge option specification

Edge

specifies an edge the endpoints of which define the origin, magnitude, and direction of the vector. The origin of the vector is located at the edge start endpoint vertex, and its tip is located at its end endpoint vertex. To reverse the direction of the vector, either middle-click the edge to reverse its sense or input a negative value for the Magnitude specification. (For a description of edge start and end vertices and the meaning of edge sense, see Section 2.3.1 of the GAMBIT Modeling Guide.)

Specifying a Vector Defined by Two Vertices

When you select the 2 Vertices option, GAMBIT defines the vector by means of the locations of two existing vertices. For this option, the lower portion of the Vector Definition form appears as shown below and includes the following specifications.

Figure 2-14: Vector Definition form—2 Vertices option specifications

Vertices:

contains two list boxes that specify vertices defining the origin (Start) and tip (End) of the vector. (NOTE: To reverse the direction of the vector, either switch the Start and End vertex specifications or input a negative value for the Magnitude specification.)

Specifying a Vector Defined by Two Points

When you select the 2 Points option, GAMBIT defines the vector by means of two point locations. For this option, the lower portion of the Vector Definition form appears as shown below and includes the following specifications.

Figure 2-15: Vector Definition form—2 Points option specifications

Coordinate Values:	contains two radio buttons that specify the point associated with the values currently displayed in the lower part of the form. The options, Point 1 and Point 2, specify the positions of the vector origin and tip, respectively. (NOTE: To reverse the direction of the vector, either switch the specifications for the two points or input a negative value for the Magnitude specification.)
Coordinate Sys	specifies the coordinate system of reference for the points that define the vector.
Type	------------------------------------------------------
Cartesian Cylindrical Spherical	specifies the type of coordinate system to be used in the current point specification.
Global | Local	specifies the location of the point with respect to either the Global or Local system.

Specifying a Vector Defined by the Current Screen View

When you select the Screen View option, GAMBIT defines the vector relative to the current orientation of the model in the graphics window. For this option, the lower portion of the Vector Definition form appears as shown below and includes the following specifications.

Figure 2-16: Vector Definition form—Screen View option specifications

Direction:

contains a group of paired radio buttons that allow you to specify the vector definition relative to the currently displayed orientation of the model in the graphics window. The six Direction options are as follows: Piercing—Out or In Horizontal—Right or Left Vertical—Up or Down For example, if you select the Piercing--In option and left-click on a graphics window quadrant, GAMBIT defines a vector pointing directly into the screen with an origin located in the center of the quadrant.

Copying an Entity

To copy an entity, you must specify three types of information:

• The name of the entity to be copied (the "parent" entity)
• The number of copies to be created
• The manner in which the copies are to be repositioned and/or reoriented relative to the parent entity

Creating a Single Copy of an Entity

When you create a single copy of an entity, GAMBIT duplicates all lower topology associated with the entity and locates the copy according to the specifications on the Move/Copy form. The final position and orientation of the copy is determined according to the same procedures employed when you move an entity. (See "Moving an Entity," above.)

Creating Multiple Copies of an Entity

When you create multiple copies of an entity, GAMBIT positions, orients, and/or scales the first copy relative to the parent entity and positions, orients, and scales each subsequent copy relative to the previous copy created. For example, if you create two copies of a rectangular brick and specify that the copies are to be translated in the x, y, and z directions, GAMBIT translates the first copy relative to the parent brick and translates the second copy relative to the first copy (see Figure 2-17).

Figure 2-17: Two translated copies of a rectangular brick

Similarly, if you create two copies of a rectangular brick and specify a scaling factor of 1.5, GAMBIT creates one copy the edges of which are 1.5 times larger than those of the parent brick and another copy the edges of which are 2.25 (= 1.5 1.5) times larger than those of the parent brick (see Figure 2-18).

NOTE: If the parent brick is offset from the scaling reference point, each copy of a multiple set of copies is displaced from the reference point according to the cumulative effect of the scaling factor. For example, if the parent brick shown in Figure 2-18 is offset by 1 unit from a reference point located at the center of the Global coordinate system, the first copy is offset by 1.5 units, and the second copy is offset by 2.25 units.

Figure 2-18: Two scaled copies of a rectangular brick

Copying Mesh Characteristics

When you copy an entity, GAMBIT allows you to copy any mesh characteristics associated with the entity. For example, if you create two copies of an edge containing 10 equally spaced mesh nodes and specify the Copy Mesh option on the Move/Copy Edges form, GAMBIT creates two copies of the edge, and each copy contains 10 equally spaced mesh nodes.

Copying Lower Topology

When you copy an entity, GAMBIT also copies all lower topology associated with the entity. For example, if you copy a rectangular brick volume using the Move/Copy Volumes form, GAMBIT creates a copy of all vertices, edges, and faces associated with the brick.

Copying Higher Topology and Connected Geometry

When you copy an entity, GAMBIT does not copy higher topology or any geometry connected to the entity. For example, if you copy an edge that constitutes part of a rectangular brick volume, GAMBIT copies only the edge.

Aligning an Entity

To align an entity, you must specify two types of parameters:

• The entity type and name
• One, two, or three pairs of vertices that define the alignment

The entity type and name determine which entity is to be moved by means of the alignment procedure. The vertex-pair specifications define the extent of the movement in each of the three spherical coordinate directions.

General Three-Step Alignment Procedure

When GAMBIT aligns an entity, it performs the following three operations in sequence.

Each step in the procedure is defined by a specified pair of existing vertices. The following example illustrates the overall alignment procedure and the effect of vertex-pair specification on the final position and orientation of an aligned face.

Alignment Example

Consider the two planar, nonaligned faces shown in Figure 2-19. Face face.1 is larger than face.2 and is parallel to the y-z coordinate plane. Face face.2 is not parallel to any coordinate plane.

Figure 2-19: Two nonaligned GAMBIT faces

There are several ways to align face.2 such that it is coincident with face.1. One possible procedure is as follows (see Figure 2-20):

1. Translate face.2 so that vertex.5 coincides with vertex.1 (Figure 2-20(a))
2. Rotate face.2 about vertex.1 so that a straight line drawn from vertex.1 to vertex.2 coincides with a straight line drawn from vertex.5 to vertex.6 (Figure 2-20(b))
3. Rotate (plane-align) face.2 about a straight line drawn from vertex.2 to vertex.1 so that a plane defined by vertex.5, vertex.6, and vertex.7 coincides with a plane defined by vertex.1, vertex.2, and vertex.3 (Figure 2-20(c))

Figure 2-20: GAMBIT face-alignment operations

To define an alignment procedure, such as that shown in Figure 2-20, you must specify vertex pairs that describe each step in the procedure. In GAMBIT, such vertex pairs are specified by means of Align forms (see below).

Align Form Specifications

Each type of entity is associated with its own Align form. For example, the Align Faces form shown in Figure 2-21 is used to align face entities. The Align Vertices, Align Edges, Align Faces, Align Volumes, and Align Groups forms differ from each other only with respect to the type of entity being aligned.

Figure 2-21: Example Align Faces form

The pairs of vertices that define the alignment are classified on each form as Translation, Rotation, and Plane Alignment vertex pairs. Each vertex pair consists of a Start vertex and an End vertex. The Start vertex corresponds to the position of the entity before it is aligned. The End vertex corresponds to the position or orientation of the entity after the alignment operation is complete.

For example, the operation illustrated in Figure 2-20 can be defined according to the following specifications on the Align Faces form.

In most cases, a given final configuration may be associated with more than one set of alignment specifications. For example, there are six different sets of alignment specifications that produce the final configuration shown in Figure 2-20(d). One set of specifications is that listed in the table above. Another set of specifications is as follows.

Effect of Vertex-Pair Specification on Orientation

The final orientation of the aligned entities depends on which vertex pairs are used to define each of the three steps in the alignment procedure. As an example of the effect of vertex-pair specification on the final orientation, consider the two rectangular faces shown in Figure 2-22. The faces are identical in shape and orientation to those shown in Figure 2-19 but are labeled more generally with respect to their vertices.

Figure 2-22: Two nonaligned rectangular faces

There are several configurations in which Face 2 may be considered to be fully aligned with Face 1. Four such configurations are shown in Figure 2-23. The following table lists one of the possible sets of vertex-pair specifications that result in each of the configurations shown in Figure 2-23.

Figure 2-23: Example alignment configurations of two faces

Aligning Lower Topology

When you align an entity, GAMBIT also aligns all lower topology associated with the entity. For example, if you align a rectangular brick volume using the Align Volumes form, GAMBIT translates, rotates, and plane-aligns all vertices, edges, and faces associated with the brick.

Aligning Higher Topology and Connected Geometry

By default, GAMBIT does not align an entity if it constitutes part of higher topology or if it is connected, either directly or indirectly, to other geometry. For example, if a vertex specified on an Align Vertices form constitutes one corner of a rectangular brick volume, GAMBIT does not perform the alignment operation specified on the form. Likewise, if a face specified on an Align Faces form is connected by means of one of its vertices to another face, GAMBIT does not perform the alignment operation.

To align an entity that constitutes part of higher topology or is connected to other geometry, select the Connected Geometry option on the Align form. When you select the Connected Geometry option, GAMBIT aligns the entity, all higher topology of which the entity is a part, and all geometry connected either to the entity or to any higher topology of which the entity is a part.

Scaling Aligned Entities

If the distances between the first two of the Start vertices differ from the corresponding distances between the End vertices, GAMBIT activates the Scale option on the Align form. The Scale option allows you to resize the aligned entity to match the distances between the End vertices to which the entity is aligned. For example, if you select the Scale option for the procedure illustrated in Figure 2-20, GAMBIT resizes face.2 so that the edge defined by vertex.5 and vertex.6 is identical in length to the corresponding edge on face.1.

Start Vertex and End Vertex Specifications

Start and End vertices specified on Align forms may exist independently of the entity or entities to be aligned. For instance, in the example presented above, the final position of face.2 does not depend on whether vertex.1, vertex.2, and vertex.3 exist separately from or constitute the corners of face.1.

If you specify a translation Start vertex that does not constitute part of the entity to be aligned, GAMBIT translates the entity relative to its current position according to the distance and direction defined by a vector drawn between the translation Start and End vertices. For instance, in the example presented above, if you specify vertex.1 as the translation Start vertex and vertex.2 as the translation End vertex—and do not specify rotation or plane-alignment vertices—GAMBIT translates face.2 as shown in Figure 2-24.

Figure 2-24: Specifying Start and End vertices not connected to face.2

Using Align Forms

Align forms allow you to reposition and/or reorient vertices, edges, faces, volumes, or groups relative to vertices already existing in the model. Each type of entity is associated with its own Align form, but all Align forms are identical with respect to the types of specifications available. Align forms differ from each other only with respect to the type of entity being aligned.

To open any Align form, click the Align command button on the Geometry subpad specific to the entity being aligned. For example, to open the Align Vertices form (Figure 2-25), click the Align command button on the Geometry/Vertex subpad.

Figure 2-25: Example Align form

Each Align form includes the following specifications.

Entities	specifies the entities to be aligned. The type of entities specified by means of the Entity list box is determined by the nature of the current Align form. For example, on the Align Vertices form, the Entity list box is titled "Vertices" and specifies one or more vertices to be aligned.
Translation Vertex Pair:	specifies the translation Start and End vertices. (See "Start Vertex and End Vertex Specifications," above.)
Rotation Vertex Pair:	specifies the rotation Start and End vertices. (See "Start Vertex and End Vertex Specifications," above.)
Plane Alignment Vertex Pair:	specifies the plane-alignment Start and End vertices. (See "Start Vertex and End Vertex Specifications," above.)
Connected Geometry	specifies that all geometry connected to the vertex is to be aligned according to the specifications on the form. (See "Aligning Higher Topology and Connected Geometry," above.)
Scale	specifies that all topology to which the vertex is connected is to be scaled to match the distances between the translation, rotation, and plane-alignment Start and End vertices. (See "Scaling Aligned Entities," above.)

© Fluent, Inc. 10/29/01