The coordinate planes (yz-plane, zx-plane, xy-plane) the space 3 into eight trihedral angles, which are called the octants of the space.  The magnitude of each octant as a solid angle is π2.

Any coordinate of a point moving in a certain octant preserves its sign (http://planetmath.org/SignumFunction).  One calls the octant, where all three coordinates are nonnegative, the first octant.  The other octants have no agreed numbering; see still http://de.wikipedia.org/wiki/Oktant_(Geometrie)Wikipedia.

Title octant
Canonical name Octant
Date of creation 2013-03-22 18:51:53
Last modified on 2013-03-22 18:51:53
Owner pahio (2872)
Last modified by pahio (2872)
Numerical id 5
Author pahio (2872)
Entry type Definition
Classification msc 51N20
Related topic QuadrantMathworldPlanetmath
Defines first octant