Spherical Trigonometry, Arc Distance Formula
Finding the shortest distance between two points on the earth given latitude and longitude. Download ARC_CALC_3, Microsoft Excel version, A Spherical Triangle Calculator by James Q. Jacobs.
Smarandache Geometries
Having at least one smarandachely denied axiom: validated and invalidated; or invalidated in at least two distinct ways. Discussion groups and meetings.
Minkowskian geometry and quaternion algebras
An exploration of the geometry of quaternion algebra, including a commutative variant which exhibits the properties of Minkowskian geometry.