= Points and vertices =

See [how to edit points|edit_points].

A _point_ is simply a point in space as defined by four numbers (X, Y,
Z, W).

A _vertex_ is a reference to a point. Primitives use vertices to
reference points. For example, the corners of a polygon, the center of a
sphere, or a control vertex of a spline curve.

Primitives can share points, while vertices are unique to a primitive.

For example, you can have polygons that have corners at an identical
location in space. The polygons may share a single point, in which case
each polygon's vertex at that corner would be a reference to the same
point. Or, those vertices may each point to unique points that happen to
have the same spacial location.

This is not merely an academic distinction. _Unique-ing the points_
(giving each vertex its own point instead of sharing points at shared
corners) with the [Facet SOP|Node:sop/facet] has several important
effects on polygons:

* Because OpenGL no longer computes shared point normals, the polygons
  are individually shaded with a flat look.

  [Image:/images/pointvtx_unique.png]

  However, you can  [pre-compute the normals|]  to preserve the smooth
  shading of the original surface.

* You can independently scale the polygon faces to create interesting
  effects.

  [Image:/images/pointvtx_uniquescale.png]

  If you  [pre-compute the normals|] , the individual pieces retain
  their shading from the original surface.

  [Image:/images/pointvtx_precomputenormals.png]

Similarly to unique-ing all points, you can use the Facet SOP to _cusp
polygons_, unique-ing points selectively based on the angle at which the
shared edges meet.