# Geometric Entities

Every point, line, surface or solid must be organized into one component, and therefore are mutually exclusive to a component.

## Points

A point is a zero-dimensional geometric entity.

A free point is a zero-dimensional geometry entity in space that is not associated with a surface. It is displayed as a small "x". These types of points are typically used for weld locations and connectors.

A fixed point is a zero-dimensional geometry entity that is associated with a surface. It is displayed as a small "o". The automesher places a node at each fixed point on the surface being meshed. A fixed point that is placed at the junction of three or more non-suppressed edges is called a vertex or vertex point. Such vertices cannot be suppressed (removed).

## Lines

A line represents a curve in space and is not attached to any surface or solid. A line is a one-dimensional geometric entity.

A line can be composed of one or more line types. Each line type in a line is referred to as a segment. The end point of each line segment is connected to the first point of the next segment. A joint is the common point between two line segments. Line segments are maintained as a single line entity, so operations performed on the line affect each segment of the line. In general, HyperMesh automatically uses the appropriate number and type of line segments to represent the geometry.

Lines are different from surface edges and are sometimes handled differently for certain operations.

## Surfaces

A surface represents the geometry associated with a physical part. A surface is a two-dimensional geometric entity that may be used in automatic mesh generation.

A surface is comprised of one or more faces. Each face contains a mathematical surface and edges to trim the surface, if required. When a surface has several faces, all of the faces are maintained as a single surface entity. Operations performed on the surface affect all the faces that comprise the surface. In general, HyperMesh automatically uses the appropriate number of and type of surface faces to represent the geometry.

The perimeter of a surface is defined by edges. There are four types of surface edges:
Free edges
A free edge is an edge that is owned by only one surface.
Free edges are colored red by default.
On a clean model consisting of surfaces, free edges appear only along the outer perimeter of the part and around any interior holes. Free edges that appear between two adjacent surfaces indicate the existence of a gap between the two surfaces. The automesher will leave a gap in the mesh wherever there is a gap between two surfaces.
Shared edges
A shared edge is an edge that is owned, or shared, by two adjacent surfaces.
Shared edges are colored green by default.
When the edge between two surfaces is a shared edge, there is no gap or overlap between the two surfaces - they are geometrically continuous. The automesher always places seed nodes along the length a shared edge and will produce a continuous mesh without any gaps along that edge. The automesher will not construct any individual elements that cross over a shared edge.
Suppressed edges
A suppressed edge is shared by two surfaces but it is ignored by the automesher.
Suppressed edges are colored blue by default.
Like a shared edge, a suppressed edge indicates geometric continuity between two surfaces but, unlike a shared edge, the automesher will mesh across a suppressed edge as if it were not even there. The automesher does not place seed nodes along the length of a suppressed edge and, consequently, individual elements will span across it. By suppressing undesirable edges you are effectively combining surfaces into larger logical meshable regions.
Non-manifold edges
A non-manifold edge is owned by three or more surfaces.
Non-manifold edges are colored yellow by default.
They typically occur at "T" intersections between surfaces or when 2 or more duplicate surfaces exist. The automesher always places seed nodes along their length and will produce a continuous mesh without any gaps along that edge. The automesher will not construct any individual elements that cross over a T-joint edge. These edges cannot be suppressed.

Surface edges are different from lines and are sometimes handled differently for certain operations.

The connectivity of surface edges constitutes the geometric topology.

## Solids

Solids are closed volume of surfaces that can take any shape. Solids are three-dimensional entities that can be used in automatic tetra and solid meshing.

The surfaces defining a solid can belong to multiple component collectors. The display of a solid and its bounding surfaces are controlled only by the component collector to which the solid belongs.

## Faces

A face is a single Non-uniform Rational B-Spline (NURBS) and is the smallest area entity. It has a separate underlying mathematical definition, specified when it was created.

All faces are represented mathematically with the following formulations:
• plane
• cylinder/cone
• sphere
• torus
• NURBS

A surface can be made up of a single face type or of multiple face types. Multiple types are used for more complex surfaces that contain sharp corners or highly complex shapes.