See how to 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 has several important effects on polygons:
Because OpenGL no longer computes shared point normals, the polygons are individually shaded with a flat look.
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.
If you pre-compute the normals , the individual pieces retain their shading from the original surface.
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.