GVNP

 Projection     : General Vertical Near-Side Perspective
 General class  : azimuthal
 Characteristics: neither conformal nor equal-area
 Earth model    : sphere

Defining the MAPUNITS:

 MapUnits "gvnp"     ! Standard name
 MapUnits "gvnp 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
 Height              "height_of_perspective"  ! Usually defined,
                                              !    if defaulted 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