Overview

N-Geometry is an integrated system for creating, modifying, and storing 3D objects. It is a window-based system that lets you create and modify objects interactively in the 3D editor.

Objects can be drawn either orthographically or in perspective. You can select the point of view, display backfacing polygons, and define other parameters that affect the display, such as hiding hidden lines.

Once you've created an object, you can manipulate all or part of it by choosing various operations from N-Geometry's menus.

The N-Geometry window provides smooth, dynamic control of the eyepoint. N-Geometry is capable of mimicking actual camera attributes, such as lens focal length, film format, angle, and point of view. N-Geometry is designed to work seamlessly with other programs in the N-World environment such as N-Dynamics (to animate objects) and N-Render (to color objects).

Using the windowing system and graphical input from a mouse, you can use one of the pre-defined commands to generate primitive polyhedra such as cubes or cylinders, then use a full range of geometric and topological operations on an object or any of its specific vertices, edges, or faces to customize it.

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The Environment

Any point in space can be uniquely defined by three numbers, the x, y, and z coordinates, which represent its distance from the three planes perpendicular to the major axes passing through the global origin. The three directions, together with the global origin, are called the global coordinate system, as shown in Figure 1.1.

In N-Geometry this coordinate system is "right-handed;" positive y represents "up," positive x is "right," and positive z is "forward."

Figure 1.1 The global coordinate system

While this global coordinate system is always in effect, it is possible for objects you create to have their own x, y, and z axes. Such coordinate systems are referred to as local coordinate systems. Local coordinate systems can have a different origin and their axes can point in different directions from the global coordinate system. Local coordinate systems can also be non-Cartesian.

The number of local coordinate systems is unlimited, but they are always defined in terms relative to the global coordinate system.

The Camera

The camera is a special kind of object, in that you never see it, but it can be moved and modified in much the same way as other N-Geometry objects, and its motion can be choreographed with animation scripts created in N-Dynamics.

Also, you can specify that the camera take on certain characteristics so that the view angle matches that of known real-world camera formats. This means that you can create animations that match certain film formats.

When talking about the camera, there are two points in space that are often referred to: a point from which the scene is viewed, called the eyepoint, and a point toward which the camera is aimed, called the aimpoint. The distance between the eyepoint and the aimpoint is called the aim-distance, and the direction from the aimpoint to the eyepoint is called the camera direction.

Figure 1.2 Camera terminology

From the eyepoint, the camera takes in a certain region of global space that is then projected onto the window. The angle between the left and right sides of this pyramid is called the view angle. Because the window is rectangular, the shape of this region is a rectangular pyramid whose apex is at the eyepoint and whose sides project away from the eyepoint toward infinity.

The region that the camera sees does not actually extend all the way from the eyepoint to infinity. Rather, it extends from some distance in front of the eye, known as the hither distance, to some far off distance, known as the yon distance. The planes perpendicular to the line of sight passing through these points are called the hither clipping plane and yon clipping plane, respectively. Only objects that fall inside the pyramid between these two planes can be visible.

Figure 1.3 Hither and yon clipping planes

The region of visibility between the hither and yon clipping planes is called the viewing volume.

Objects

• a body
• a transformation matrix

Figure 1.4 Components of an object

The body can be one of two things:

• a basic geometric entity, called a geobody
• a group of other objects

The transformation matrix is a set of numbers that can modify the appearance of the object.

Body

A geobody is an entity that holds all the essential geometric and topological information of an object, as shown in Figure 1.5. It is what makes an object recognizable as a form-what makes a cube a cube. It is frequently built up from other geometric entities, called elements, but is itself self-contained.

A cube, for example, is a polyhedron comprised of six face elements, which in turn are defined by vertex elements located at particular points in space and topologically interconnected in a certain way by edge elements. Among the geobodies defined by N-Geometry are isolated points and line segments, wires (contiguous segments), and polyhedra.

Figure 1.5 Object with a geobody for its body

While a geobody is a unique entity, it cannot be viewed or manipulated in
N-Geometry without being instanced, that is, being the body of some object, as shown in Figure 1.6. It is possible for two (or more) objects to share a single geobody. A geobody which belongs to more than one object is said to be multi-instanced. (You can create a multi-instanced object with the Reinstance command, described elsewhere in this manual.)

Figure 1.6 Reinstanced objects

An object whose body is a group of objects is called a compound object. Each member of the group is an object complete with its own body and transformation matrix, and can in turn be either a simple or compound object, as shown in Figure 1.7. With repeated nesting, a single object can consist of hundreds of geobodies.

Figure 1.7 Compound object

Transformation Matrix

When you modify the matrix, you are, in effect modifying the coordinate system in which the object is embedded. It does not affect the body of the object at all but only its appearance in the world. The raw data of a body exists in the local coordinate system of the body's object, which is initially coincident with the global coordinate system.

When you modify the transformation matrix of the object you separate the local coordinate system from the global coordinate system. For example, a polyhedron might have all its vertices centered around the origin. Applying a translation transformation to the polyhedron's object displaces the space in which the polyhedron is defined. The polyhedron's vertices are still centered around the local origin but are now far from the global origin because the local space has moved relative to the global coordinate system.

When there is no difference between the local coordinate space of an object and the global coordinate space (that is, when applying the object's transformation matrix leaves the object in the same position from which it started), the transformation matrix is said to be an identity matrix.

Each object, including an object that has been reinstanced, has a unique transformation matrix. This is what makes sharing geobodies feasible, since you can make a single geobody appear to be in different locations with different sizes or shapes simply by belonging to objects with different transformation matrices.

The matrix itself is an array of sixteen numbers that is used to change the drawn position of each point in an object. Because it is such a small data structure, it is easy to change and can be considered more volatile than the geometric information in the body. N-Dynamics, for example, replaces the values in the transformation matrices of animated objects with its own numbers.

An object can be forced into the global coordinate system by a process called Apply Transformation. This transfers all of the information in the object's transformation matrix into the raw data of the body. This action effectively shifts the local coordinate system out from underneath the body, thereby making the body coincide with the global coordinate system. The apparent position of an object becomes its home position.

Transform vs. Modify

• Transformations are those operations performed on an entire object. To perform a transformation, you select objects on the element sensitivity menu.
• Modifications are changes made to the body of an object. These affect only the elements of the object's body. To perform a modifcation, you select points, segments, or bodies on the element sensitivity menu.

Many effects can be generated by changing an object's transformation matrix or changing the body itself (e.g., with functions that move, scale, or rotate an object or body).

Modifications to the body change the data in each primitive element of the body, while changes to the transformation matrix affect only the appearance of the object. It is easy to initialize (erase) the transformation matrix to undo any changes made to the appearance. Changes made to a body, however, are permanent, and can only be undone by subsequent opposite changes (using the Undo operation).

Operations are specified relative to some coordinate system:

• When you transform an object, the transformation can be applied in any coordinate space. When you transform an object, you can generally use different mouse clicks execute the command in local space, inthe object's superior's local space, or in global space.
• When you modify a body, the modifications are always executed in local coordinate space of the body's object.

Object Hierarchy

Figure 1.8 shows the hierarchy of a top-level object, which is represented by the single rectangle at the top. It has for its body a list of objects. The objects that make up the list are represented by the four rectangles immediately below the top-level object.

The leftmost rectangle has for its body a geobody, in this case an icosahedron. The hexagonal shape between the object and body is a body-display-item (bdi) which is inserted and used by the 3D editor for storing display information.

The middle two inferior objects are instanced. They share the same geometric information, but their transformation matrices and bdis (represented by hexagons) are different. The two objects might look completely different from one another.

The rightmost inferior object is a compound object and is itself made up of a list of objects.

Figure 1.8 Hierarchy of a top-level object

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The 3D Editor

Figure 1.1 Geometry frame

The following paragraphs give brief descriptions of the different parts of the N-Geometry window.

The Sensitivity Element Menu

• points
• segments
• faces
• bodies
• objects

The none entry deselects all elements, and collect option lets you select a group of elements on which you want to perform the same operation.

Once an element is highlighted, it can be selected so various operations can be performed on it. See the section "Selecting Elements," on page 1-34.

The View Window

The Camera Motion Menu

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The GeoMenus

Figure 1.2 The GeoMenus window

When you see commands like (CLICK-L) on GeoMenus>File>New Object, it means to (CLICK-L) on the New Object command under the File section of the GeoMenus.

File

Camera

Object Display

Utilities

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The Mouse Monitor Window

Figure 1.3 The Geometry Monitor menu

The elements displayed in the mouse monitor window change depending on the action you're performing in N-Geometry:

When moving the camera, the following values may be displayed:

Table 1.1 Camera parameters for the mouse monitor window

Parameter	Description
xe, ye, ze	X, Y, and Z coordinates of the camera eyepoint.
xa, ya, za	X, Y, and Z coordinates of the camera aimpoint.
azm alt rll	Azimuth, altitude, and roll (camera's orientation).
vu	View angle.
ht yn	Hither and yon plane values.

The values displayed in the mouse monitor window depend on which camera mode is selected from the camera sensitivity menu along the bottom of the N-Geometry window.

When editing an element in N-Geometry, the following values may be displayed:

Table 1.2 Camera parameters for the mouse monitor window

Parameter	Description
dx, dy, dz	Relative motion along X, Y, and Z axes.
dist	Relative single axis motion.
da, db, dc	Relative rotation around three axes.
ang	Relative single axis rotation.
xfac, yfac, zfac	Other 3-axis values (e.g., with Free Scale, shows scaling factor along each axis)
amt	Other single value (e.g. Scale along a single axis)

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Commonly Performed Geometry Tasks

Left, Middle, and Right Mouse Clicks

Figure 1.4 Selecting a command

Here are some guidelines for understanding how operations are mapped to the mouse:

• (CLICK-L) to select the simplest operation.
• (CLICK-M) selects the next level of complexity.
• (CLICK-R) is usually the most complex option, almost always asking for additional from a pop-up menu. (CLICK-R) is also commonly used to perform an operation on several elements.

Consider the Extrude command, for example:

• (CLICK-L) extrudes the selected element along its normal.
• (CLICK-M) extrudes the element, but also lets you move it freely in 3D space.
• (CLICK-R) lets you select an axis from a menu along which to extrude the element.

For other commands (for example, the XYZ Rotate command), left, middle, and right might let you specify an axis along which to perform the operation (e.g., left=X, middle=Y, and right=Z).

How can you keep track of what each mouse click does? As you move the cursor over a command, read the mouse documentation line at the bottom of the screen! If there are multiple options for a command, they are always described in the mouse documentation line.

Other Mouse Clicks

For example, if you wanted to extrude a face by an exact amount, you would (SHIFT-L) on the face, then (CTRL-L) on the Extrude command. A dialog box showing the face's current location would be displayed:

Figure 1.5 Specifying changes numerically

Enter a value for how far you want to extrude the face, then (CLICK-L) on Axis Move. The dialog box displayed for entering numeric arguments to an operation vary, depending on which parameters are required to execute the move.

Constraining Mouse Movement

Try this:

1. Create a cube.

2. (SHIFT-L) on a point on the cube.

3. (CLICK-L) on Move.

Hold down the SHIFT key and move the mouse left and right; the selected point moves only along the global X axis, as shown in Figure 1.6

4. Let up on the SHIFT key to resume normal mouse movement.

The mouse is constrained to the initial direction of the mouse after you press the SHIFT key, so you can constrain movement along they Y axis (moving the mouse up or down) or the Z axis (holding the middle mouse button down).

Working with Object Lists

Figure 1.7 Object list

In the dialog box above:

• The Default Point Light is a top-level object.
• The Door Group is a compound object; it contains three inferior objects.
• The Door Group above, for example, is the superior object to three other terminal objects-Door, Window, and Handle.

An object's relative position in the hierarchy is shown by how far it is indented.

• (CLICK-L) on an object to select that object.
• (CLICK-R) on an object to open its hierarchy and view its inferiors. The Restructure command lets you change how objects are structured.

Note. An object's position in the object hierarchy is also displayed in the mouse documentation line. A quick glance at the description of the object can tell you its relative position in an object or group's hierarchy.

Working with Text Edit Boxes

Figure 1.8 A text edit box

To change the text in a text edit box:

• (CLICK-L) to position the cursor in the box
• Use (CTRL-F) or (CTRL-B) to move back and forth
• (CLICK-M) to clear the text edit box completely and enter a new string

Specifying Objects, Directories, & Projects

If, for example, you (CLICK-L) on Export, an object list appears.

Figure 1.9 Object list

You'd (CLICK-L) on the object you wanted to export, and get the following export menu:

Figure 1.10 Object list

The object you selected above would be displayed, along with your default directory (usually your home directory).

If you wanted to change which object you were saving, you could now (CLICK-L) on the text edit box to display the object list again.

To change the directory in which you want to save the object, you have three options:

• (CLICK-L) to position the cursor in the text edit box and enter the directory manually
• (CLICK-M) to clear the text edit box completely and enter a new directory
• (CLICK-R) to display a list of directories associated with the current project (or to add a new directory to the current project).

Figure 1.11 Selecting a new directory

A project is nothing more than a series of directories that you group together logically. If you are working on an animation project, you might create a project of directories in which to store the different elements (e.g., objects, scripts, images, maps, etc.).

The Specify a new Directory command adds other directories to the list at the top of the menu; directories with asterisks ("*") next to them are temporary (not part of the project).

When you choose Specify a new Directory, a blank text edit box appears; enter the name of the directory you want to add to the list of available directories:

The newly specified directory appears in the current directory list at the top of the projects menu. To make the directory part of a project, choose Edit Current Project, then highlight any directories you want to add to the project.

Projects are described in more detail in the Getting Started manual.

• To begin camera motion, (CLICK-M) in the view window and move the mouse. (CLICK-L) when the camera is in the new, desired position.
• To abort the current camera motion, (CLICK-R).
• To halt camera motion for a single command, (CTRL-R) on the viewport window, then execute the desired command from the menu. When the menu disappears, the camera is still active.

Constraining Camera Movement

N-Geometry lets you constrain camera movements so that the camera responds to either vertical or horizontal movements of the mouse. This constraint is useful when you are trying to preserve a particular value.

To constrain mouse movement, hold down the CTRL key while you move the mouse during interactive camera operations; the camera moves only in the direction of the initial mouse movement. For example, if you hold down the CTRL key while you are in pan mode and move the mouse to the left or right, the up/down angle of the camera remains constant and the camera pans only left and right.

Camera Motion Menu

Figure 1.13 The camera motion menu

zoom +

• (CLICK-L) to change the zoom of the camera; this is similar in effect to zooming in on an object with a camera using a telephoto lens.

Then (CLICK-M) to start the camera and move the mouse up and down to adjust the view angle. This puts the camera in truck mode (moving toward and away from the aimpoint). This is similar to physically moving toward the object.

Note. While these two modes appear identical, the first changes the lens characteristic of the camera, while the second moves the camera object.

By alternately zooming and using truck mode, you can adjust the perspective effects while keeping the size of the object on the screen relatively constant.

• (CLICK-M) lets you set the hither and you clipping planes using the mouse.


• Move the mouse with no button pressed to adjust the hither plane

  
  

• (HOLD-M) to adjust the yon plane:

  

Figure 1.14 Hither and yon clipping planes

Note. Remember that there are clipping planes for each of the three axes; all three are modified as you make adjustments with the mouse.

• (CLICK-R) opens a menu that lets you set several camera parameters including projection method (perspective or orthographic), lens type, view angle, hither and yon planes, and whether auto ranging is on or off.

Rotate

• (CLICK-L) swings the camera. During a swing, the camera follows a circular path around a particular aimpoint, constantly reorienting itself to remain fixed on this aimpoint. By default, this is the global axes coordinates.
• (CLICK-M) pans the camera. Rotates the camera around its own center.
• (CLICK-R) lets you set an explicit orientation for the camera:

Figure 1.15 Setting a new camera orientation

• azimuth sets the orientation of the camera with relation to the global center; aligning the camera along the X axis sets these values to
  (90 0 0) (rotation around the Y axis).

  
  

• altitude rotates the camera around the Z axis.

  
  

• roll tilts the camera from side to side around its local axis (pointing from the eyepoint to the aimpoint).

• (CLICK-L) moves the camera. A linear translation with fixed-aim on. The camera compensates for its displacement by panning to maintain the aimpoint.
• (CLICK-M) shifts the camera. A linear translation with constant camera orientation. The aimpoint shifts with the camera.
• (CLICK-R) lets you set an explicit eyepoint with the following menu:

Figure 1.16 Setting a new camera location

Camera Modifiers

• (CLICK-L) on rotate or translate starts the camera with fixed-aim on.
• (CLICK-M) on rotate or translate starts the camera with fixed-aim off.
• (CLICK-R) on rotate or translate to set explicit values from the keyboard for the motion types.

Global

If global is not enabled, a local coordinate system is in effect; the rotation and motion axes are determined by the camera's local x, y, and z axes, and the rotation depends upon the camera's orientation.

Fixed-aim

When fixed-aim is off, the aimpoint moves with the camera. Objects seems to "drift" in the view window.

To numerically specify an aimpoint, (CLICK-R) on fixed-aim to bring up the following menu:

Figure 1.17 Setting a new aim point

Camera Motions

• When global is enabled, motion axes are parallel to the displayed axes.
• When global is disabled, the motion axes are determined by the camera's frame of reference.
• During moves and swings, the camera remains aimed at a point no matter where the camera is moved.
• During pans and shifts, the camera's aimpoint is free to move. An object at which the camera was aimed would appear to drift in the view window in a direction opposite to that of the mouse movement.

Swing Global

As the camera moves, it orients itself to remain fixed on the aimpoint. An object being viewed remains centered in the view window.

The motion axes are parallel to the global axes.

(This mode is especially helpful because it lets you view the object from any side.)

Figure 1.18 Swing global camera move

Swing Local

The rotation is based on the camera's orientation instead of the global coordinate system.

The motion axes are determined by the angle of the camera.

Figure 1.19 Swing local camera move

Pan Global

The rotation axes are parallel to the global axes.

The camera does not reorient itself to remain aimed at the object; the aimpoint moves with the mouse.

An object that is being viewed appears to drift through the view window in a direction opposite to the mouse movement.

Figure 1.20 Pan global camera move

Pan Local

The camera rotates on axes that are determined by the camera's orientation, not by the global axes. The rotation axes are determined by the camera's frame of reference and are not necessarily parallel to the global axes.

Figure 1.21 Pan local camera move

Move Global

The camera changes its orientation to remain pointed at the aimpoint.

An object that is being viewed appears to move along one of the global axes while it remains centered in the view window.

Figure 1.22 Move global camera move

Move Local

The motion axes are not parallel to the displayed axes but are determined by the angle of the camera.

Figure 1.23 Move local camera move

Shift Global

Figure 1.24 Shift global camera move

Shift Local

The motion axes are not parallel to the displayed axes but are determined by the camera's frame of reference.

Figure 1.25 Shift local camera move

Modifying Bodies

• points (0 dimensional)
• segments (1 dimensional)
• faces (2 dimensional)
• bodies (3 dimensional)

The operations you can perform on those elements include moving, scaling, rotating, cutting, collapsing, beveling, extruding, mirroring, twisting, randomizing, and so forth.

You can perform operations on elements of a polyhedron or on the elements of a wire. The elements that make up a wire are called winged segments, which are equivalent to edges of a polyhedron, and nodes, which are similar to a polyhedron's vertices.

Selecting Elements

1. Select the element type you want to modify in the element sensitivity menu.

2. Move the mouse over the element you want to modify.

Once you have selected an element type, moving the mouse over the object in the view window causes elements of that type to be highlighted (see Figure 1.26.)

3. When the element you want to modify is highlighted, (SHIFT-L) directly on the element.

The modify menu displayed is context sensitive; that is, only the operations that can be performed on the selected element type are displayed in the menu.

In most cases the element remains selected after each operation is executed, so you can do another operation on it without have to reselect the element.

Deselecting an Element

• you (CLICK-L) in an open area of the N-Geometry window
• you select a different element type on the element sensitivity menu

Collect Mode: Working with Several Elements at Once

• Select each element individually and perform the operation on one element at a time.
• Use collect mode to collect all of the desired elements of one type into a group, then perform the operation on all of them at once.

Starting a Collection

• (CLICK-L) on the element type you want to work with, then (CLICK-L) on Collect

or

• (CLICK-R) on the element type

As an example of how to collect elements, assume you want to perform an operation on several faces.

1. (CLICK-R) on a faces in the element sensitivity menu.

Note that collect is automatically highlighted in the element sensitivity menu.

Continue to select faces until all the ones you want are selected.

Note. Clicking on an already collected element removes it from the collection.

3. (CLICK-R) to complete the collection.

Figure 1.27 A collection of faces on a grid

Note. (CTRL-R) temporarily halts collect mode. (You might use this, for example, if you want to move the object to select an element that is currently obscured.) You can execute any geometry command and then immediately return to collect mode.

Ending a Collection

• (CLICK-R) on the N-Geometry window (as described above)

or

• Move the mouse off the edge of the view window

Note. An operation done on a collected group does not always give the same result as when the operation is performed sequentially on individual elements.

Growing or Shrinking a Collection

• (CLICK-L) on an element you want in your collection.
• (CTRL-L) to grow the collection outward from the already collected elements.
• (ALT-L) to shrink the collection.

Figure 1.28 Growing a collection

You can grow collections of point, edges, or faces. Growing a collection is handy when you want to collect multiple elements that are obscured or that would require you to turn the camera repeatedly.

Using the Lasso to Collect Elements

• (ALT-L) on the view window to start a 2D collection. While holding down the (L) mouse button, use the mouse to draw a line around the elements you want to collect. When you release the mouse button, N-Geometry completes the lasso for you and selects the elements within the loop.
• (ALT+CTRL-L) starts a 3D collection, including polygons on back of the model. Elements must fall within the area drawn by the lasso to be included in the collection.

Figure 1.29 A 2D collection of grid faces using the lasso

• (ALT+CTRL+SHIFT-L) also starts a 3D collection; however, an element need only be partially clipped to be included in a selection.

Figure 1.30 Collecting the same faces using (ALT+CTRL+SHIFT)-elements need only be touched by the lasso

Saving a Collection

1. Create a collection.

2. (CLICK-R) to end collect mode.

3. (SHIFT-L) on the collection, then (CLICK-L) on Add to Part to make the collection a part.

Enter a name for the part in the dialog box that appears

(CLICK-M) on Parts to open a menu that lets you do the following:

• Delete one or more parts.
• Rename a part.
• Select the elements of one or more parts.
• Select All except selects all elements on the object except those in the selected part.
• Select Intersection select those elements that occur in all of the chosen parts.

Moving Objects and Elements

Moving Objects with the Mouse

• to modify along the x axis, move the mouse left or right
• to modify along the y axis, move the mouse forward and backward
• to modify along the z axis, move the mouse forward and backward while holding down the middle button (denoted as (HOLD-M) in the body text).

Moving Objects Using Numeric Menus

Figure 1.31 Specifying changes numerically

To make specifying numeric parameters the default, go to the Utilities>Preferences>Element Edit and set Numeric Input Default to Yes. This menu item causes numeric value menus to come up each time you select a geometric operation. (In this mode, you can still specify mouse-controlled operation by holding the CTRL key when you select the operation.)

Moving Pop-up Windows

To move a pop-up window:

1. Move the mouse over the pop-up window.

2. Press ALT+F7.

The menu is highlighted in red.

Magnet Moves

For example, as the selected vertex is pulled, the vertices within the defined area are pulled along with the selected vertex as if influenced by it. The effect of the influence is greatest on the vertices closest to the selected vertex and falls off for the vertices toward the outer edge of the sphere. The rate of fall off can also be controlled. The effect of the influence is 100% on the selected element and gradually decreases to no effect at the outer edge of the defined area.

To enable an operation to influence an area:

1. (SHIFT-L) on the element you want to modify.

2. (ALT-L) on Move.

While the original element stays highlighted in the 3D editor, you select a second point in the scene (not necessarily on the same object), that defines the range of influence for the operation.

Note how not only the originally selected element, but other vertices, move as well.

Figure 1.32 Specifying an area of influence numerically

Defining an Area of Influence

• Distance route specifies the method used to determine the area of influence.


• Midpoint creates an imaginary point that is located at the "center" of an element or the current collection of elements; the outer edge of influence is measured from this midpoint of that element or collection.

  

Figure 1.33 Measuring from the midpoint

The sphere of influence tends to produce a more "bloated" or "puffy" appearance in a modified shape when using operations such as Move.

• Shortest measures directly from the element to the assigned distance. If the area of influence is measured from a single point, the Shortest and Midpoint methods are identical.

  Because there are really a number of smaller area of influences being calculated, using this method tends to cause topological changes to retain the shape of the selected element or elements.

  
  
• Surface measures from the element in a somewhat straight line, except that the line of measure tends to follow edges.

  

Because the area of influence is measured along the surface, modifying a shape with commands like Move tend to keep the shape of the object.

Note. This method is most useful if you are performing an operation on an irregular surface.

• Falloff determines the type of curve used to determine how the influence of the operation falls off as you approach the edge of the area of influence.


• Straight uses an inverse linear curve; influence decreases linearly from the center.

  
  

• Spike uses an inverse square curve; influence decreases quickly near the center, more slowly at the edge.

  
  

• Bell use a cosine curve; influence decreases slowly at the center and edge, quicker in between.

  
  

• Dome uses a half-cosine curve; influence decreases gradually at the center, more quickly at the edge.

• Influence dist lets you specify the distance used for calculating the area of influence. If you use either the Midpoint or Shortest methods, the distance represents the radius of the "invisible" sphere. If you use the Surface method, it represents the distance measured along the surface of the object.

The default values for these parameters can be found in Utilities>Preferences>Element Edit.

Operations That Need an Axis

Figure 1.35 Choosing a value for an axis

If, for example, you were to (CLICK-R) on Extrude with a face selected, you'd be presented with the menu above, so you could specify an axis along which the operation was to be performed.

Each of the entries on this menu is described below:

• This Element's Normal selects the current element's normal as the axis value.

For an edge, the normal is the average of the normals of the two adjacent faces. For a vertex, the normal is the average of the normals of the adjacent faces. Polyhedra have no normal. Requesting that a polyhedron move along its normal moves it along its local y axis.

• Select Normal lets you selects the normal of any element; after selecting this option, move the mouse over the view window and (CLICK-L) on the element whose normal you want to use
• Select a Segment selects any segment, edge or rotation axis to use as an axis.
• Select element pair selects any two elements and use the direction between them as the axis.
• [X], [Y], and [Z]


• (CLICK-L) on X, Y, or Z to use one of the object's local axes.

  
  

• (CLICK-M) to use the global x, y, or z axis.

  
  

• (CLICK-R) to use the local x, y, or z axis of another object.

• Camera selects an axis relative to the current camera view (relative to screen):


• (CLICK-L) selects the axis going left and right across the screen.

  
  

• (CLICK-M) selects the axis going up and down across the screen.

  
  

• (CLICK-R) selects the Z axis from the eyepoint to the aimpoint.

• Eyepoint to Object selects the axis from the eyepoint to an object's local origin.
• Type in Cartesian Direction defines a direction based on two sets of xyz coordinates you supply.
• Type in Spherical Orientation defines an arc along which to move the element. The dialog box asks for three coordinates to define this arc: the first is the longitude, the second the latitude, and the third the radius from the center point of the object to the point on the imaginary sphere.

Operations That Need an Origin

In cases where an origin point has significance, the following menu is displayed, which lets you select the origin point:

Figure 1.36 Choosing an origin point

• Cursor brings up a three-arm cursor that you can move to any position on the screen.
• This Element's Midpoint uses the midpoint of the selected element as the origin.
• Object Midpoint uses the midpoint of an object as the origin.
• Origin uses the object's local origin, the global origin, or the origin of another object (depending on whether you click left, middle, or right).
• Aimpoint uses the point toward which the N-Geometry camera is aimed as the point of origin.
• Eyepoint uses the N-Geometry camera location as the point of origin.
• Type In Location lets you type in an absolute origin using the xyz coordinates.
• Select Element uses a vertex or the center of segment or face as the origin.
• Point along Segment lets you specify a location on a segment of your choosing as the origin.

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Shortcuts

To define the current default operation:

1. Select an element and perform the operation on it.

2. Move the mouse over an empty area of the N-Geometry window and use (CTRL+SHIFT-L).

A message appears in the upper left corner of the 3D editor, telling you that the last operation you used is now the default operation.

Once a default operation has been defined, you use (CTRL-L) as a shortcut for (SHIFT-L) + selecting the operation.

Note. After you've defined the current default operation, you can select a different element type (e.g., a point instead of a segment) and still use (CTRL-L) to apply the current default operation to the selected element.

Hotkeys

• To display the hot keys available, press "h" with the mouse over the N-Geometry window.
• For a more complete description of the hot keys, see Appendix B, "Hot Keys" at the endo of this guide.

Copyright © 1996, Nichimen Graphics Corporation. All rights reserved.