The IPositionVector type exposes the following members.
Adjust the position vector of an object for aberration of light
Adjust the position vector for precession of equinoxes between two given epochs
Adjust the position vector for proper motion (including foreshortening effects)
Initialize the PositionVector from a Site object and Greenwich apparent sidereal time.
Initialize the PositionVector from a Site object using UTC Julian date and Delta-T
Initialize the PositionVector from a Star object.