# 3D Geometry Terminology

It is important to be familiar with this terminology as it is used extensively in the user interface and documentation. There are two categories of geometry:

Reference Geometry

There are various kinds of 3D reference geometry. Some exist as default geometry in every part, such as the 3 default planes and 3 default axes. You will often create additional reference geometry to achieve various modeling tasks. Reference geometry has no size, per se. You can imagine planes and axes to the extent of infinity, even though they do not visually do so when you look at them.

### Planes

A plane is a flat, two-dimensional surface that extends infinitely. Because they are flat (2D), you will often find yourself creating 2D Sketches on them as the first step in creating many 3D Features. Each part and assembly has 3 default planes: XY, YZ, and ZX.

### Axes

An axis is a one-dimensional line that extends infinitely. Axes are typically used as centerlines, for example during a Revolve command or for a Circular Pattern. Each part and assembly has 3 default axes: X, Y, and Z.

### Points

Points (or Nodes) are single points in space. You can create points to define important locations in space and then reference them from multiple different sketches, for example. Each part and assembly has one default point: the Origin, located at 0,0,0.

## Coordinate System

The coordinate system of each part or assembly has its 0,0,0 point at the Origin. The Origin is the only default point in a part or assembly. Through the origin, the 3 default axes extend in the X, Y, and Z directions. Through the origin and through each combination of Axes extend the default planes, defining the XY, YZ, and ZX planes.

### Changing the Coordinate System

There is no way to modify the coordinate system of a part directly. A workaround is to Boolean Unite a part (A) into a blank new part (B), during which you can adjust the orientation and placement of part (A) within part (B).

## Model Geometry

### Faces

A Face is defined as any surfaces that make up a solid object. Planes can be inserted onto faces and all edges that constitute a face can be filleted. Sketches can be created on planar faces as well as holes. Faces are also used for constraining purposes when working with assemblies.

The faces, edges, and vertices of a part will be displayed in the Design Explorer when a part is created. These items are renumbered each time a part is modified.

## Edges

Edges represent the end of a face or feature. Edges are listed in the Design Explorer along with the faces and vertices that define a part. All edges are renumbered each time a feature is applied to a part. The last edge created will always be listed first and labeled as Edge<1>.

Note: Secondary operations may be applied to a selected edge by using the Insert Fillet, Insert Chamfer, and Insert Axis tools.

## Vertices

A Vertex is a point that represents the intersection of multiple edges. A vertex can be chamfered, annotations can be inserted on a vertex, measurements between vertices can be taken, and extrusions or holes can be placed at a target vertex.

Vertices can only be selected in a part workspace or in the Edit Part Mode of an assembly workspace. The faces, edges, and vertices of a part are listed in the Design Explorer when the part is created.

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