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

Definitions 1

Of an angle 1.1

Of a polytope 1.2

Of a plane tiling 1.3

Principal vertex 2

Vertices in computer graphics 3

See also 4

References 5

External links 6
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.^{[1]}
Of a polytope
A vertex is a corner point of a polygon, polyhedron, or other higherdimensional polytope, formed by the intersection of edges, faces or facets of the object.^{[1]}
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 ( 180°, two right angles) ; otherwise, it is called "concave" or "reflex".^{[2]} 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 1skeleton of a polytope is a graph, the vertices of which correspond to the vertices of the polytope,^{[3]} and in that a graph can be viewed as a 1dimensional 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.^{[4]} 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;^{[5]} 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 zerodimensional faces.
Principal vertex
Vertex B is an ear, because the straight line between C and D is entirely inside the polygon. Vertex C is a mouth, because the straight line between A and B is entirely outside the polygon.
A polygon vertex x_{i} 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.^{[6]}
Ears
A principal vertex x_{i} of a simple polygon P is called an ear if the diagonal [x_{(i−1)},x_{(i+1)}] that bridges x_{i} lies entirely in P. (see also convex polygon)
Mouths
A principal vertex x_{i} of a simple polygon P is called a mouth if the diagonal [x_{(i−1)},x_{(i+1)}] lies outside the boundary of P.
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;^{[7]} these properties are used in rendering by a vertex shader, part of the vertex pipeline.
See also
References

^ ^{a} ^{b}

(3 vols.): ISBN 0486600882 (vol. 1), ISBN 0486600890 (vol. 2), ISBN 0486600904 (vol. 3). Heath's authoritative translation of Euclid's Elements plus his extensive historical research and detailed commentary throughout the text.

^ Jing, Lanru; Stephansson, Ove (2007). Fundamentals of Discrete Element Methods for Rock Engineering: Theory and Applications. Elsevier Science.

^ Peter McMullen, Egon Schulte, Abstract Regular Polytopes, Cambridge University Press, 2002. ISBN 0521814960 (Page 29)

^ Alexander I. Bobenko, Peter Schröder, John M. Sullivan, Günter M. Ziegler (2008). Discrete differential geometry. Birkhäuser Verlag AG.

^ M.V. Jaric, ed, Introduction to the Mathematics of Quasicrystals (Aperiodicity and Order, Vol 2) ISBN 0120406020, Academic Press, 1989.

^

^ Christen, Martin. "Clockworkcoders Tutorials: Vertex Attributes".
External links
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