.help ccsystems Mar00 astcat
.ih
NAME
ccsystems -- list and describe the supported coordinate systems
.ih
USAGE
help ccsystems
.ih
CATALOG ACCESS COORDINATE SYSTEMS

Astcat supports several catalog access coordinate systems and manages all the
required transformation between them based on input from the user and
information in the catalog configuration file.

.ls The Input Coordinate System
The input coordinate system specifies the coordinate system
of the region center coordinates used to extract data from a
catalog. The input coordinate
system is normally defined by the user. If undefined, the input coordinate
system defaults to the query coordinate system.
.le
.ls The Query Coordinate System
The query coordinate system specifies the coordinate system of the coordinates
used to formulate a catalog query. The query coordinate
system is normally defined in the catalog configuration file.
If undefined the query coordinate system defaults to the catalog
coordinate system. Coordinates in the input coordinate system
must be transformed to the query coordinate system in order to formulate
a correct query.
.le
.ls The Catalog Coordinate System
The catalog coordinate system is the coordinate system of the astrometric
catalog. The catalog coordinate system is normally defined in the catalog
configuration file. If undefined it defaults to J2000.
.le
.ls The Output Coordinate System
The output coordinate system is the coordinate system of the output
catalog produced by the catalog query. Normally the output coordinate
system is defined by the user. If undefined it default to the catalog
coordinate system. Catalog coordinates are transformed from the catalog
coordinate system to the output coordinate system before they are
written to the output file.
.le

.ih
IMAGE ACCESS COORDINATE SYSTEMS

Astcat supports several image access coordinate systems and manages the
required transformation between them based on input from the user, and
information in the return image headers and the image survey configuration
file.

.ls The Input Coordinate System
The input coordinate system specifies the coordinate system of the region
center coordinates used to extract data from an image survey. The input
coordinate system is normally defined by the user. If undefined, the input
coordinate system defaults to the query coordinate system.
.le
.ls The Query Coordinate System
The query coordinate system specifies the coordinate system of the coordinates
used to formulate an image survey query. The query coordinate system is
normally defined in the image survey configuration file.  If undefined the
query coordinate system defaults to J2000.  Coordinates in the input coordinate
system must be transformed to the query coordinate system in order to formulate
a correct query.
.le
.ls Image Coordinate System
The image coordinate system is the coordinate system stored in the header
of the fits image returned by an image survey query. The image coordinate
system type is specified in the image survey configuration file. The
currently recognized types are "fits", "dss", and "none". The default
image coordinate system type is none. The dss wcs is always in the
J2000 system. The fits headers may be in any supported coordinate systems,
but the most common system is J2000.
.le
.ls the output coordinate system
The output coordinate system is the coordinate system of the final image
stored in the image header in FITS format.  The output coordinate system
may be the same as the image coordinate system but encoded differently
as when a dss coordinate system is converted to its fits equivalent,
or different as when an image without a coordinate system is assigned
one by the user.
.le

.ih
CELESTIAL COORDINATE SYSTEMS

The astcat package supports the equatorial ("fk4", "fk4-noe", "fk5", "icrs"),
ecliptic, galactic, and supergalactic celestial coordinate systems. In most
cases and unless otherwise noted users can input their coordinates in
any one of these systems as long as they specify the coordinate system
correctly.

Considerable flexibility is permitted in how the coordinate systems are
specified, e.g. J2000.0, j2000.0, 2000.0, fk5, fk5 J2000, and fk5 2000.0
all specify the mean place post-IAU 1976 or FK5 system. Missing equinox and
epoch fields assume reasonable defaults. In most cases the
systems of most interest to users are "icrs", "j2000", and "b1950"
which stand for the ICRS J2000.0, FK5 J2000.0 and FK4 B1950.0 celestial
coordinate systems respectively. The full set of options are listed below:

.ls equinox [epoch]
The equatorial mean place post-IAU 1976 (FK5) system if equinox is a
Julian epoch, e.g. J2000.0 or 2000.0, or the equatorial mean place
pre-IAU 1976 system (FK4) if equinox is a Besselian epoch, e.g. B1950.0
or 1950.0. Julian equinoxes are prefixed by a J or j, Besselian equinoxes
by a B or b. Equinoxes without the J / j or B / b prefix are treated as
Besselian epochs if they are < 1984.0, Julian epochs if they are >= 1984.0.
Epoch is the epoch of the observation and may be a Julian
epoch, a Besselian epoch, or a Julian date. Julian epochs
are prefixed by a J or j, Besselian epochs by a B or b.
Epochs without the J / j or B / b prefix default to the epoch type of
equinox if the epoch value <= 3000.0, otherwise epoch is interpreted as
a Julian date.  If undefined epoch defaults to equinox.
.le
.ls icrs [equinox] [epoch]
The International Celestial Reference System where equinox is
a Julian or Besselian epoch e.g. J2000.0  or B1980.0.
Equinoxes without the J / j or B / b prefix are treated as Julian epochs.
The default value of equinox is J2000.0.
Epoch is a Besselian epoch, a Julian epoch, or a Julian date.
Julian epochs are prefixed by a J or j, Besselian epochs by a B or b.
Epochs without the J / j or B / b prefix default to Julian epochs
if the epoch value <= 3000.0, otherwise epoch is interpreted as
a Julian date.  If undefined epoch defaults to equinox.
.le
.ls fk5 [equinox] [epoch]
The equatorial mean place post-IAU 1976 (FK5) system where equinox is
a Julian or Besselian epoch e.g. J2000.0  or B1980.0.
Equinoxes without the J / j or B / b prefix are treated as Julian epochs.
The default value of equinox is J2000.0.
Epoch is a Besselian epoch, a Julian epoch, or a Julian date.
Julian epochs are prefixed by a J or j, Besselian epochs by a B or b.
Epochs without the J / j or B / b prefix default to Julian epochs
if the epoch value <= 3000.0, otherwise epoch is interpreted as
a Julian date.  If undefined epoch defaults to equinox.
.le
.ls fk4 [equinox] [epoch]
The equatorial mean place pre-IAU 1976 (FK4) system where equinox is a
Besselian or Julian epoch e.g. B1950.0  or J2000.0,
and epoch is the Besselian epoch, the Julian epoch, or the Julian date of the
observation.
Equinoxes without the J / j or B / b prefix are treated
as Besselian epochs. The default value of equinox is B1950.0. Epoch
is a Besselian epoch, a Julian epoch, or a Julian date.
Julian epochs are prefixed by a J or j, Besselian epochs by a B or b.
Epochs without the J / j or B / b prefix default to Besselian epochs
if the epoch value <= 3000.0, otherwise epoch is interpreted as
a Julian date.  If undefined epoch defaults to equinox.
.le
.ls noefk4 [equinox] [epoch]
The equatorial mean place pre-IAU 1976 (FK4) system but without the E-terms
where equinox is a Besselian or Julian epoch e.g. B1950.0 or J2000.0,
and epoch is the Besselian epoch, the Julian epoch, or the Julian date of the
observation.
Equinoxes without the J / j or B / b prefix are treated
as Besselian epochs. The default value of equinox is B1950.0.
Epoch is a Besselian epoch, a Julian epoch, or a Julian date.
Julian epochs are prefixed by a J or j, Besselian epochs by a B or b.
Epochs without the J / j or B / b prefix default to Besselian epochs
if the epoch value <= 3000.0, otherwise epoch is interpreted as
a Julian day.  If undefined epoch defaults to equinox.
.le
.ls apparent epoch
The equatorial geocentric apparent place post-IAU 1976 system where
epoch is the epoch of observation.
Epoch is a Besselian epoch, a Julian epoch or a Julian date.
Julian epochs are prefixed by a J or j, Besselian epochs by a B or b.
Epochs without the J / j or B / b prefix default to Besselian
epochs if the epoch value < 1984.0, Julian epochs
if the epoch value <= 3000.0, otherwise epoch is interpreted as
a Julian date.
.le
.ls ecliptic epoch
The ecliptic coordinate system where epoch is the epoch of observation.
Epoch is a Besselian epoch, a Julian epoch, or a Julian date.
Julian epochs are prefixed by a J or j, Besselian epochs by a B or b.
Epochs without the J / j or B / b prefix default to Besselian epochs
if the epoch values < 1984.0, Julian epochs
if the epoch value <= 3000.0, otherwise epoch is interpreted as
a Julian day.
.le
.ls galactic [epoch]
The IAU 1958 galactic coordinate system.
Epoch is a Besselian epoch, a Julian epoch or a Julian date.
Julian epochs are prefixed by a J or j, Besselian epochs by a B or b.
Epochs without the J / j or B / b prefix default to Besselian
epochs if the epoch value < 1984.0, Julian epochs
if the epoch value <= 3000.0, otherwise epoch is interpreted as
a Julian date. The default value of epoch is B1950.0.
.le
.ls supergalactic [epoch]
The deVaucouleurs supergalactic coordinate system.
Epoch is a Besselian epoch, a Julian epoch or a Julian date.
Julian epochs are prefixed by a J or j, Besselian epochs by a B or b.
Epochs without the J / j or B / b prefix default to Besselian
epochs if the epoch value < 1984.0, Julian epochs
if the epoch value <= 3000.0, otherwise epoch is interpreted as
a Julian date. The default value of epoch is B1950.0.
.le

Fields enclosed in [] are optional with the defaults as described. The epoch
field for the "icrs" , "fk5", "galactic", and "supergalactic" coordinate
systems is only used if the input coordinates are in the equatorial fk4,
noefk4, fk5, or icrs systems and proper motions are used to transform from
coordinate system to another.

.ih
SEE ALSO
.endhelp