PDS_VERSION_ID = PDS3
LABEL_REVISION_NOTE = "2005-05-10, Bryan Stiles, Version 1.2"
RECORD_TYPE = STREAM
INSTRUMENT_HOST_ID = CO
INSTRUMENT_ID = RADAR
TARGET_NAME = TITAN
OBJECT = DATA_SET_MAP_PROJECTION
DATA_SET_ID = "CO-SSA-RADAR-5-BIDR-V1.0"
OBJECT = DATA_SET_MAP_PROJECTION_INFO
MAP_PROJECTION_TYPE = "OBLIQUE CYLINDRICAL"
MAP_PROJECTION_DESC = "
Because of the highly variable geometry of the Cassini spacecraft's
encounters with Titan and the elongated shape of the Synthetic
Aperture Radar (SAR) footprints, the standard Simple Cylindrical
coordinate system would be extremely inefficient for representing
individual basic images. Therefore, the Cassini Basic Image Data
Record (BIDR) products are produced in an Oblique Cylindrical
map projection. This type of projection is a Cartesian plot of
the angular (longitude and latitude) coordinates of features,
not with respect to the standard coordinate axes of the body,
but with respect to a rotated set of axes. A separate oblique
coordinate system is established for each Titan pass, placing the
equator of the rotated coordinates along the ground track of that
Cassini flyby and the rotated prime meridian through the point of
closest approach.
The Oblique Cylindrical projection is characterized by the 3x3
rotation matrix between the standard and oblique coordinate systems
or the equivalent set of angles, which are interpretable as the
(north) pole latitude, pole longitude, and pole rotation.
Projection Definition
---------------------
The following PDS keywords define an instance of an oblique
cylindrical projection with respect to the standard IAU/IAG
positive west longitude planetographic latitude coordinate
system. The projection is defined both by a rotation matrix and
the equivalent set of angles.
OBLIQUE_PROJ_POLE_LATITUDE = fff.ffffff One of the three
angles defining the oblique coordinate system used in the OBLIQUE
CYLINDRICAL projection. This is the ordinary latitude of the
pole (Z axis) of the oblique system.
OBLIQUE_PROJ_POLE_LONGITUDE = fff.ffffff One of the three
angles defining the oblique coordinate system used in the OBLIQUE
CYLINDRICAL projection. This is the ordinary longitude of the
pole (Z axis) of the oblique system. NOTE that the value given
is positive-west, whereas the equivalent positive-east value is
used in the equations that define the OBLIQUE_PROJ_POLE_ROTATION
and the rotation matrix entries below.
OBLIQUE_PROJ_POLE_ROTATION = fff.ffffff One of the three
angles defining the oblique coordinate system used in the OBLIQUE
CYLINDRICAL projection. This is a rotation around the polar
(Z) axis of the oblique system that completes the transformation
from standard to oblique coordinates. The value is positive east
(obeys right hand rule) and is in the range 0 to 360 degrees.
OBLIQUE_PROJ_X_AXIS_VECTOR = {ff.ffffffff, ff.ffffffff,
ff.fffffffff} Unit vector in the direction of the X axis of
the oblique coordinate system used in the OBLIQUE CYLINDRICAL
projection, in terms of the X, Y, and Z axes of the standard
body-fixed coordinate system. In each system, the X axis
points from the body center toward longitude and latitude (0,0)
in that system, the Z axis to (0,90), and the Y-axis completes
a right-handed set. The OBLIQUE_PROJ_X/Y/Z_AXIS_VECTORS make
up the rows of a rotation matrix that when multiplied on the
left of a vector referenced to the standard coordinate system
converts it into its equivalent in the oblique coordinate system.
This rotation matrix is the product of successively applied
rotations by OBLIQUE_PROJ_POLE_LONGITUDE around the Z axis,
90 - OBLIQUE_PROJ_POLE_LATITUDE around the once-rotated Y axis,
and OBLIQUE_PROJ_POLE_ROTATION around the twice-rotated Z axis.
OBLIQUE_PROJ_Y_AXIS_VECTOR = {ff.ffffffff, ff.ffffffff,
ff.fffffffff} Unit vector in the direction of the Y axis of
the oblique coordinate system used in the OBLIQUE CYLINDRICAL
projection, in terms of the X, Y, and Z axes of the standard
body-fixed coordinate system. In each system, the X axis
points from the body center toward longitude and latitude (0,0)
in that system, the Z axis to (0,90), and the Y-axis completes
a right-handed set. The OBLIQUE_PROJ_X/Y/Z_AXIS_VECTORS make
up the rows of a rotation matrix that when multiplied on the
left of a vector referenced to the standard coordinate system
converts it into its equivalent in the oblique coordinate system.
This rotation matrix is the product of successively applied
rotations by OBLIQUE_PROJ_POLE_LONGITUDE around the Z axis,
90 - OBLIQUE_PROJ_POLE_LATITUDE around the once-rotated Y axis,
and OBLIQUE_PROJ_POLE_ROTATION around the twice-rotated Z axis.
OBLIQUE_PROJ_Z_AXIS_VECTOR = {ff.ffffffff, ff.ffffffff,
ff.fffffffff} Unit vector in the direction of the Z axis of
the oblique coordinate system used in the OBLIQUE CYLINDRICAL
projection, in terms of the X, Y, and Z axes of the standard
body-fixed coordinate system. In each system, the X axis
points from the body center toward longitude and latitude (0,0)
in that system, the Z axis to (0,90), and the Y-axis completes
a right-handed set. The OBLIQUE_PROJ_X/Y/Z_AXIS_VECTORS make
up the rows of a rotation matrix that when multiplied on the
left of a vector referenced to the standard coordinate system
converts it into its equivalent in the oblique coordinate system.
This rotation matrix is the product of successively applied
rotations by OBLIQUE_PROJ_POLE_LONGITUDE around the Z axis,
90 - OBLIQUE_PROJ_POLE_LATITUDE around the once-rotated Y axis,
and OBLIQUE_PROJ_POLE_ROTATION around the twice-rotated Z axis.
Lat/Lon to Line/Sample Transformations
------------------------------------
The transformations between the oblique latitude and longitude
and the line and sample coordinates of the data products are
line = INT( LINE_PROJECTION_OFFSET + lon_a*MAP_RESOLUTION + 1)
sample = INT(SAMPLE_PROJECTION_OFFSET + lat_a*MAP_RESOLUTION + 1)
where lon_a and lat_a are the oblique cylindrical pole longitude
and pole latitude measured in degrees, and lon_a is in
positive-east coordinates. Integral values of line and sample
correspond to the center of a pixel. LINE_PROJECTION_OFFSET,
SAMPLE_PROJECTION_OFFSET, and MAP_RESOLUTION are defined below.
LINE_PROJECTION_OFFSET is the line offset value of the map
projection origin position from the line and sample (1,1), i.e.,
the upper left corner of the array. The value is positive when
the origin is below the upper left pixel. (The map projection
origin is the intersection of the equator and the projection
center longitude; this location is stored as the values of the
CENTER_LATITUDE and CENTER_LONGITUDE keywords. Both keywords are
nominally zero valued.)
SAMPLE_PROJECTION_OFFSET is the sample offset value of the map
projection origin position from the line and sample (1,1), i.e.,
the upper left corner of the array. The value is positive when
the origin is to the right of the upper left pixel.
MAP_RESOLUTION identifies the digital scale of the map-projected
image in units of pixels per degree.
Definitions of other mapping parameters can be found in the
Planetary Science Data Dictionary and the Cassini Radar Basic
Image Data Records Software Interface Specification.
"
ROTATIONAL_ELEMENT_DESC = "See SEIDELMANNETAL2002"
OBJECT = DS_MAP_PROJECTION_REF_INFO
REFERENCE_KEY_ID = "SEIDELMANNETAL2002"
END_OBJECT = DS_MAP_PROJECTION_REF_INFO
OBJECT = DS_MAP_PROJECTION_REF_INFO
REFERENCE_KEY_ID = "SNYDER1987"
END_OBJECT = DS_MAP_PROJECTION_REF_INFO
OBJECT = DS_MAP_PROJECTION_REF_INFO
REFERENCE_KEY_ID = "BUGAYEVSKIY&SNYD1995"
END_OBJECT = DS_MAP_PROJECTION_REF_INFO
OBJECT = DS_MAP_PROJECTION_REF_INFO
REFERENCE_KEY_ID = "YANGETAL2000"
END_OBJECT = DS_MAP_PROJECTION_REF_INFO
OBJECT = DS_MAP_PROJECTION_REF_INFO
REFERENCE_KEY_ID = "GREELEY&BATSON1990"
END_OBJECT = DS_MAP_PROJECTION_REF_INFO
END_OBJECT = DATA_SET_MAP_PROJECTION_INFO
END_OBJECT = DATA_SET_MAP_PROJECTION
END