The procedure also accepts a list of features, with 
  either missing performs mappings between pixel coordinates,
  latitude/longitude pairs, and planet-relative coordinates.
  

  Feature = RECORD
      name: TEXT;       (* Texture name (arbitrary string) *)
      img: LR2.T;       (* Pixel coordinates, or "(Huge,Huge)" if undef. *)
      lat, lng: LONG;   (* Latitude and longitude,  or "(Huge,Huge)" if undef. *)
      pos: LR3.T;       (* Planet coordinates, or [0,0,0] if undef. *)
    END;
  Features = ARRAY OF Feature;