General

The Polygon menu cell commands in the Model module allow you to modify an existing polygon mesh object by adding or removing:

• Vertices (points)
• Edges (a line between two points)
• Polygons (the surface face bounded by the lines)

You can select polygons on objects and then duplicate, delete, or apply transformations to those polygons according to the local (polygon-specific) coordinate system.

These commands are useful for modelling details or for creating polygonal patterns that are to be coloured using the Polygon (Matter Module) menu cell.

For an overview of polygon modelling, see the Modelling Selected Polygons section of the Modelling User's Guide.

Procedure

1. Select a polygon mesh object.
2. Choose the appropriate command.

Vertex

Allows you to add or remove vertices from a polygon mesh object.

• Left mouse button adds a vertex at the point you pick when you pick an edge.
• Middle mouse button adds a vertex to the middle of the picked edge.
• Right mouse button removes the vertex you pick.

Edge

Allows you to add or remove edges from a polygon mesh object.

• Left mouse button adds a single edge between two vertices. Pick the first vertex, then the second.
• Middle mouse button allows you to add a series of connected edges by picking the first vertex, picking the second to create the edge, then picking a third to create an edge between the second and the third, and so on.
• Right mouse button removes the edge that you pick.

Polygon

If you want to draw new polygons on an existing polygon mesh object, you must first attach them to existing ones using this command. It picks existing vertices of polygons to which the new polygon is attached.

A related command, Draw->Polygon, represents the "drawing" mode. It lets you create new vertices to define the outline of a new polygon.

You don't have to keep switching between the two commands: the selections are toggled for you and the mode switching is handled seamlessly.

For the complete procedure for creating your own polygon mesh object, see the Drawing a Polygon Mesh section of the Modelling User's Guide.

Rules for Adding Polygons

You can either:

• Fill the "empty" space of a deleted polygon.
• Add a new polygon off an existing one. The existing polygon must have an open edge.

In all cases:

• You can only add a polygon to an open edge. To help you see which edges are open, select the Edge Flags command in the Show menu cell. When you activate this option, open edges are green; closed edges are white.
• To keep the same surface normals, you must draw the new polygon in the same direction that the existing ones were drawn. In most cases, this means drawing counterclockwise, to maintain surface normals pointing outward.

The error message "Bad edge orientation" is displayed if you try to add polygons onto a closed edge, or tag the vertices in the wrong direction for surface normals.

1. If you are starting from an existing polygon, choose Polygon->Polygon.
2. The status line says "Add Polygon". The new mouse line prompts are:

• Left mouse button: Picks a vertex on an existing polygon to which any new polygon will be attached.
• Middle mouse button: Accepts the current polygon. The status line message reads" "The polygon has been added to the mesh".
• Right mouse button: Ends the additive mode. The status line message reads "Polygon creation aborted".

3. Left-click on at least two vertices on the object. Picked vertices are highlighted in yellow. The status line says: "Select vertex #n of the polygon".
4. If you left-click anywhere off the object, you return to the "draw" mode and prompts, as you are now defining a vertex to the new polygon.
5. If you left-click on another existing vertex of the object, you remain in "attach" mode; the new polygon (when completed) will also be attached to this vertex of the object.
6. Keep picking or drawing vertices off in space to make a polygon of the desired shape.
7. To complete the polygon, middle-click. The completed polygons are added to the mesh.
8. Repeat the operation until you have the desired polygon mesh object.
9. When satisfied with the object, middle-click.

Select Commands

You can use these commands in manipulation modes (OBJ, TAG, CRT, TXT or POL) to select polygons of a polygon mesh object using procedures described in Selecting Polygons on an Object of the Modelling User's Guide.

To delete or transform these selected polygons, you must be in POL mode. You can also manipulate adjacent polygons according to a shared coordinate system or independently, as described in Transforming Adjacent Polygons of the Modelling User's Guide.

For a detailed description of polygon coordinate systems, duplication, and transformations, see the Modelling Selected Polygons section of the Modelling User's Guide.

Select by Tag Vertex

This command allows you to select one or more polygons on an object by tagging their vertices. This method may select both the intended polygon and the one directly "behind it" on the other side of the 3D object. Check that only the intended polygon is selected before starting to model with it.

Select by Rectangle

This command (or the y Supra key) allows you to select a polygon using the click-and-drag mouse selection method to draw a rectangle around it.

This method may also select both the intended polygon and the one directly "behind it" on the other side of the 3D object. Check that only the intended polygon is selected before starting to model with it.

Select by Raycasting

This command (or the g Supra key) allows you to select a polygon by clicking on it.

Unlike the Polygon->Select by Tag Vertex and Select by Rectangle commands, this selects only the polygon nearest the camera. As a result, you do not inadvertently select the polygon directly behind your selection on the other side of the 3D object.

Reference Frame

A reference frame is a null object with its coordinate system aligned with that of the selected polygon(s) on a polygon mesh object. You create such a reference object using this command.

You can use a reference null in any number of ways:

• You could apply constraints in the Actor or Motion module.
• Since the null lines up with the centre and local x, y, or z axes of a polygon on a mesh, you can draw in precise reference to that centre.

For example, suppose you wanted to have a ball move along a path in the y-axis. In the Top window, select a polygon on the ball object to create a reference null with the interest on y-axis. Draw the curve (the path) in the Front window; the curve begins exactly at the centre of the selected polygon and extends up its y-axis. You could then use path animation to make a ball or other object move along that path.

 

Procedure

1. Select a polygon mesh object.
2. Select one or more polygons on the object. It is easiest to do this using the g Supra key or the Polygon->Select by Raycasting command.
3. Choose the Polygon->Reference Frame command. You do not need to be in POL mode to use this command.

A null object is created for each selected polygon according to the previous description.

Last updated 02-apr-1998