OBJECT                           = DATA_SET_MAP_PROJECTION_INFO

  MAP_PROJECTION_TYPE             = STEREOGRAPHIC

  MAP_PROJECTION_DESC             = "

    In the polar stereographic projection, parallels of latitude are
    circles centered on the pole, and meridians of longitude are
    straight lines radiating from the pole.

    Images in this projection are centered on either the North or South
    pole, with the central longitude (specified by the CENTER_LONGITUDE
    value in the image label) running vertically from the pole to the
    bottom of the image for the North Polar projection, and to the top
    of the image for the South Polar projection.

    The transformation from latitude and longitude (LAT, LON) in radians
    to LINE and SAMPLE is given by the following equations.

    SCALE = 1737.4/MAP_SCALE

    North Polar Stereographic:

        SAMPLE = SAMPLE_PROJECTION_OFFSET + 
                 2*SCALE*SIN(LON-CENTER_LONGITUDE)*TAN(PI/4-LAT/2)+0.5

        LINE = LINE_PROJECTION_OFFSET + 
               2*SCALE*COS(LON-CENTER_LONGITUDE)*TAN(PI/4-LAT/2)+0.5

    South Polar Stereographic:

        SAMPLE = SAMPLE_PROJECTION_OFFSET + 
                 2*SCALE*SIN(LON-CENTER_LONGITUDE)*TAN(PI/4+LAT/2)+0.5

        LINE = LINE_PROJECTION_OFFSET - 
               2*SCALE*COS(LON-CENTER_LONGITUDE)*TAN(PI/4+LAT/2)+0.5

    In the above definitions, integral values of LINE and SAMPLE
    correspond to the center of a pixel, and the top left image pixel
    has LINE=1 and SAMPLE=1. LAT and LON are the latitude and longitude
    of a given spot on the surface in radians.

    LINE_PROJECTION_OFFSET

      is the image line number minus one on which the map projection
      origin occurs.  The map projection origin is the appropriate pole.

    SAMPLE_PROJECTION_OFFSET

      is the nearest image sample number to the left (west) of the
      projection longitude CENTER_LONGITUDE.

    CENTER_LONGITUDE

      is the value of the projection longitude.  For this dataset, this
      field is always 0.0.

    MAP_SCALE

      pixel spacing at the projection origin, which is the appropriate
      pole for stereographic images.  The value is in units of
      kilometers/pixel.

    MAP_RESOLUTION

      number of pixels per degree at the projection origin, which is
      the appropriate pole for stereographic images."

  ROTATIONAL_ELEMENT_DESC         = "See DAVIESETAL1989."

  OBJECT                          = DS_MAP_PROJECTION_REF_INFO

   REFERENCE_KEY_ID               = "SNYDER1987"

  END_OBJECT                      = DS_MAP_PROJECTION_REF_INFO

 END_OBJECT                       = DATA_SET_MAP_PROJECTION_INFO

END