The Encyclopedia of Triangle Centers (ETC) is an online list of thousands of points or "
centers" associated with the geometry of a
triangle
A triangle is a polygon with three corners and three sides, one of the basic shapes in geometry. The corners, also called ''vertices'', are zero-dimensional points while the sides connecting them, also called ''edges'', are one-dimension ...
. This resource is hosted at the
University of Evansville
The University of Evansville (UE) is a private university in Evansville, Indiana. It was founded in 1854 as Carnegie Hall of Moores Hill College, Moores Hill College. The university operates a satellite center, Harlaxton Manor, Harlaxton College ...
. It started from a list of 400 triangle centers published in the 1998 book Triangle Centers and Central Triangles by Professor
Clark Kimberling.
, the list identifies 68,547 triangle centers and is managed cooperatively by an international team of geometry researchers. The encyclopedia is integrated into
Geogebra.
Each point in the list is identified by an index number of the form ''X''(''n'') —for example, ''X''(1) is the
incenter.
The information recorded about each point includes its
trilinear and
barycentric coordinates and its relation to lines joining other identified points. Links to
The Geometer's Sketchpad diagrams are provided for key points. The encyclopedia also includes a glossary of terms and definitions.
Each point in the list is assigned a unique name. In cases where no particular name arises from geometrical or historical considerations, the name of a star is used instead. For example, the 770th point in the list is named ''point
Acamar''.
Notable points
The first 10 points listed in the encyclopedia are:
:
Other points with entries in the encyclopedia include:
:
Similar, albeit shorter, lists exist for quadri-figures (quadrilaterals and systems of four lines) and polygon geometry.
See also
*
Catalogue of Triangle Cubics
*
List of triangle topics
*
Triangle center
*''
The Secrets of Triangles''
*
Modern triangle geometry
References
External links
*
*
Implementation of ETC points as Perl subroutinesby Jason Cantarella
Encyclopedia of Quadri-figuresEncyclopedia of Polygon Geometry
{{Authority control
Triangle centers
Mathematical databases
20th-century encyclopedias
21st-century encyclopedias