OG

 Projection     : Orthographic
 General class  : azimuthal
 Characteristics: neither conformal nor equal-area
 Earth model    : sphere

Defining the MAPUNITS:

 MapUnits "og"       ! Standard name.
 MapUnits "og e19"   ! Standard name and ellipsoid

Other parameters:

 TrueOriginLongitude "longitude_of_origin"  ! Required, for True origin
 TrueOriginLatitude  "latitude_of_origin"   ! Required, for True origin
 FalseEasting        "false_easting"        ! Optional, default is zero
 FalseNorthing       "false_northing"       ! Optional, default is zero

Possible errors:

 E334, "Point cannot be projected" - In converting from geographic 
        coordinates to projection 
        coordinates, the point cannot be projected.
 E100, "Invalid data" - In converting from projection coordinates 
        to geographic coordinates, there was an input data error