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