the functions of the anglescan package support the following map projections. for a description of the different projections, see, for example, https://en.wikipedia.org/wiki/Map_projection

Selector	Projection	Function	Properties
kProjDist = 0	azimuthal equidistant	r = c * theta	radius is proportional to polar angle.
kProjStereo = 1	stereographic	r = c * tan theta/2	circles on sphere map to circles.
kProjArea = 2	azimuthal equal-area	r = c * sin theta/2	preserves area measure.
kProjGnom = 3	gnomonic	r = c * tan theta	great circles map to straight lines.
kProjOrtho = 4	orthographic	r = c * sin theta	k-space mapping in ARPES and LEED.

the projections in this package are defined for 0 <= theta < 90.