Vertex (geometry)


Vertex (geometry)

In geometry, a vertex (plural vertices) is a special kind of point that describes the corners or intersections of geometric shapes.

Contents

Definitions

Of an angle

A vertex of an angle is the endpoint where two line segments or lines come together.

The vertex of an angle is the point where two rays begin or meet, where two line segments join or meet, where two lines intersect (cross), or any appropriate combination of rays, segments and lines that result in two straight "sides" meeting at one place.

Of a polytope

A vertex is a corner point of a polygon, polyhedron, or other higher dimensional polytope, formed by the intersection of edges, faces or facets of the object.

In a polygon, a vertex is called "convex" if the internal angle of the polygon, that is, the angle formed by the two edges at the vertex, with the polygon inside the angle, is less than π radians; otherwise, it is called "concave" or "reflex". More generally, a vertex of a polyhedron or polytope is convex if the intersection of the polyhedron or polytope with a sufficiently small sphere centered at the vertex is convex, and concave otherwise.

Polytope vertices are related to vertices of graphs, in that the 1-skeleton of a polytope is a graph, the vertices of which correspond to the vertices of the polytope, and in that a graph can be viewed as a 1-dimensional simplicial complex the vertices of which are the graph's vertices. However, in graph theory, vertices may have fewer than two incident edges, which is usually not allowed for geometric vertices. There is also a connection between geometric vertices and the vertices of a curve, its points of extreme curvature: in some sense the vertices of a polygon are points of infinite curvature, and if a polygon is approximated by a smooth curve there will be a point of extreme curvature near each polygon vertex. However, a smooth curve approximation to a polygon will also have additional vertices, at the points where its curvature is minimal.

Of a plane tiling

A vertex of a plane tiling or tessellation is a point where three or more tiles meet; generally, but not always, the tiles of a tessellation are polygons and the vertices of the tessellation are also vertices of its tiles. More generally, a tessellation can be viewed as a kind of topological cell complex, as can the faces of a polyhedron or polytope; the vertices of other kinds of complexes such as simplicial complexes are its zero-dimensional faces.

Principal vertex

A polygon vertex xi of a simple polygon P is a principal polygon vertex if the diagonal [x(i − 1),x(i + 1)] intersects the boundary of P only at x(i − 1) and x(i + 1). There are two types of principal vertices: ears and mouths.

Ears

A principal vertex xi of a simple polygon P is called an ear if the diagonal [x(i − 1),x(i + 1)] that bridges xi lies entirely in P. (see also convex polygon)

Mouths

A principal vertex xi of a simple polygon P is called a mouth if the diagonal [x(i − 1),x(i + 1)] lies outside the boundary of P. (see also concave polygon)

Vertices in computer graphics

In computer graphics, objects are often represented as triangulated polyhedra in which the object vertices are associated not only with three spatial coordinates but also with other graphical information necessary to render the object correctly, such as colors, reflectance properties, textures, and surface normals; these properties are used in rendering by a vertex shader, part of the vertex pipeline.

See also

External links


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Look at other dictionaries:

  • Vertex — (Latin: corner; plural vertices or vertexes) may refer to:Mathematics*Vertex (geometry), a corner point of a polygon, polyhedron, tesselation, etc. *Vertex (graph theory), a node in a graph *Vertex (curve), a local extreme point of curvature… …   Wikipedia

  • Vertex Shader — (auch Vertexshader, Abk. VS) sind Programme, die in der Regel vom Grafikprozessor einer 3D Grafikkarte im Verlauf der Grafikpipeline (in den sogenannten Shadereinheiten) ausgeführt werden. Häufig werden auch die Shadereinheiten selbst als Vertex… …   Deutsch Wikipedia

  • Vertex-Shader — (auch Vertexshader, Abk. VS) sind Programme, die in der Regel vom Grafikprozessor einer 3D Grafikkarte im Verlauf der Grafikpipeline (in den sogenannten Shadereinheiten) ausgeführt werden. Häufig werden auch die Shadereinheiten selbst als Vertex… …   Deutsch Wikipedia

  • Vertex shader — (abbreviation VS ) is a shader program, normally executed on the Graphics processing unit. Function A vertex shader is a graphics processing function used to add special effects to objects in a 3D environment. Programming Vertex shaders are… …   Wikipedia

  • vertex — (n.) 1560s, the point opposite the base in geometry, from L. vertex highest point, lit. the turning point, originally whirling column, whirlpool, from vertere to turn (see VERSUS (Cf. versus)). Meaning highest point of anything is first attested… …   Etymology dictionary

  • vertex — ► NOUN (pl. vertices or vertexes) 1) the highest point; the top or apex. 2) Geometry each angular point of a polygon, polyhedron, or other figure. 3) a meeting point of two lines that form an angle. 4) Anatomy the crown of the head. ORIGIN Latin …   English terms dictionary

  • Geometry shader — Shader Un shader (anglais, du verbe to shade : ombrager ou estomper, nuancer) est un programme[Quoi ?] utilisé en image de synthèse pour paramétrer une partie du processus de rendu réalisé par une carte graphique ou un moteur de rendu… …   Wikipédia en Français

  • Vertex shader — Shader Un shader (anglais, du verbe to shade : ombrager ou estomper, nuancer) est un programme[Quoi ?] utilisé en image de synthèse pour paramétrer une partie du processus de rendu réalisé par une carte graphique ou un moteur de rendu… …   Wikipédia en Français

  • Vertex Shader — Shader Un shader (anglais, du verbe to shade : ombrager ou estomper, nuancer) est un programme[Quoi ?] utilisé en image de synthèse pour paramétrer une partie du processus de rendu réalisé par une carte graphique ou un moteur de rendu… …   Wikipédia en Français

  • Vertex and pixel shaders — Shader Un shader (anglais, du verbe to shade : ombrager ou estomper, nuancer) est un programme[Quoi ?] utilisé en image de synthèse pour paramétrer une partie du processus de rendu réalisé par une carte graphique ou un moteur de rendu… …   Wikipédia en Français


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