Vertices, Faces, Edges, Lines and Components

In case you are wondering what the word ‘vertices’ means, it is the rather pedantic plural of the word vertex --- use ‘vertexes’ if you prefer. Also, a vertex is just a fancy word for a point in 3D space. Vertices and faces alone determine the geometry of objects in Ligno3D Designer.

The rhombic dodecahedron (file Rhombohedron.lig) in the illustration has 12 faces, 14 vertices, and 24 edges. Individual faces can be selected by clicking on them with the left mouse button. When selected, a face turns yellow and its face number appears in the Status Bar. Vertices are the corners where three faces meet. They are selected by clicking the green vertex handles. These turn yellow when selected and their corresponding vertex numbers are shown in the Status Bar. Edges are selected by clicking on the blue edge handles. Vertex and edge handles can be turned on and off using the Vertex Handles and Edge Handles buttons in the Select Toolbar. Vertex and face numbers can be turned on and off with the Vertex Numbers and Face Numbers

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Vertices L3DD’s vertices are numbered points in 3D space that have X, Y and Z coordinates. They need not be attached to faces. Each vertex can be moved about freely in 3D space, deforming faces and objects in the process. Unattached vertices can be deleted, but where vertices belong to faces the faces must be deleted first. Most deleted vertices are not really deleted. They are ‘sent to heaven’ --- made to plot at the highest possible Y value. They are truly deleted only when vertices are renumbered. This strategy prevents renumbering of vertices whenever a vertex is ‘deleted’.

Faces As far as L3DD is concerned a face is just a list of vertices. For faces to display shiny-side out the vertices are listed in anticlockwise order. If they are listed in clockwise order the face will be drawn dull-side out, and if they are listed in some other order the face will not be drawn correctly. Faces are given a number that stays with the face, no matter how many other faces are deleted. If you delete a face its vertices remain, even if the face is isolated from all others. If you move a shared vertex it affect the shape of all faces that share it. If a face has more than three edges it becomes warped if one of its vertices is moved out of the plane of the face. Plane Mode allows you to move vertices within the plane of a face, regardless of its orientation. You can use the Unwarp Faces command to divide warped faces into the minimum number of smaller planar faces.

Edges L3DD does not keep a list of edges. They exist only in the presence of a face and are identified in the Status Bar by the vertex numbers at each end of the edge. You cannot have an edge between two isolated vertices. Nevertheless, edges can be moved around as if they are separate entities by using edge handles that can be toggled on and off. Edges are deleted only when the face that contains them is deleted.

Lines Lines (as distinct from edges) are not used much in L3DD, but they are there to depict things like guy-ropes for tents, or cords for suspending a gondola beneath a balloon. A line is a face with only two vertices. It is created by clicking on vertex 1, vertex 2 and then vertex 1 again, and it appears as a non-reflecting line two pixels wide. It can be selected, moved and deleted in the same way as any face, except that its ‘face number’ is not displayed in the 3D View. However, its ‘face number’ can be seen in the Status Bar when the line is selected

Components Components are faces that have been grouped together under a descriptive title. The little blue house has several components, the most obvious being the ‘Compound Roof’, as the component is called. The list of component names is kept in alphabetic order. Components are optional, and many projects do not bother with them. However, they can be useful for manipulating objects such as the columns in the ‘GreekTemple.lig’ file, or for segregating parts of a project for printing, etc. Lone vertices can not belong to a component. The Thick Faces command automatically creates panel components, both plain and dovetailed. The Create Frame command also creates components.

Vertex and face numbers do not have to change during the editing of an object. However, some will change if you use the Clean-Up command, or Renumber Vertices or Faces. The Clean-Up command is commonly used at the end of the design process.

The term ‘plane’ is used in L3DD to refer conceptually to flat planar surfaces that extend indefinitely in all ‘in-plane’ directions. Although planes are usually defined by selecting a face, they extend beyond the bounding edges of the face. Vertices may be created using the Line-Plane, Three-Plane and Closest-Point Vertex commands that lie in these planes, but outside the bounding edges of the faces used to define the planes. They may also lie outside the current viewing volume, and thus be difficult to find!