Performs a tessellation of the unit sphere.
This class generates the coordinates of the triangles that will
tessellate the unit sphere. The algorithm is recursive subdivision
of an initial representation which can be tetrahedral, octahedral or
icoshedral. The default is icosahedral. The number of points generated
depends on the level of subdivision. The default is 4 levels and with the
initial icoshedral representation this gives 1536 points.
The constants for the tetrahedral and icosahedral representations were
taken from http://eeg.sourceforge.net/eegdoc/eeg_toolbox/sphere_tri.html