#### NAME

v - get or set the current vertex context

#### SYNOPSIS

v [ id [ = [ template ] ] ]

#### DESCRIPTION

If the v keyword is given by itself, then it establishes the unnamed vertex context, which is the origin with no normal. This context may be modified, but the changes will not be saved. (The unnamed vertex is never used except as a source of default values since all geometric entities call their vertices by name.)

If the keyword is followed by an identifier id, then it reestablishes a previous context. If the specified context was never defined, an error will result.

If the entity is given with an identifier followed by an equals sign ('='), then a new context is established, and cleared to the default vertex (the origin). (Note that the equals sign must be separated from other arguments by white space to be properly recognized.) If the equals sign is followed by a second identifier template, then this previously defined vertex will be used as a source of default values instead. This may be used to establish a vertex alias, or to modify an existing vertex and give it a new name.

A non-zero vertex normal must be given for certain entities, specifically ring and torus require a normal direction. An f entity will interpolate vertex normals if given, and use the polygon plane normal otherwise. See the prism entry for an explanation of how it interprets and uses vertex normals. The other entities ignore vertex normals if present.

The actual position and normal direction for a vertex is determined at the time of use by a geometric entity. Specifically, the transformation in effect at the time the vertex is defined is irrelevant. The only transformation that matters is the one that is applied to the geometry itself. This prevents double-transformation of vertices and allows one set of vertices to be used for multiple purposes, e.g. the front and back sides of a drawer.

#### EXAMPLE

```# Make a capped cylinder
v end1 =
p 0 0 0
n 0 0 -1
v end2 =
p 0 0 1
cyl end1 1.2 end2
# Forgot normal for end2
v end2
n 0 0 1
ring end1 0 1.2
ring end2 0 1.2
```