IRA_CREAT

Create an identifier for specified astrometry information

Description:

The supplied astrometry information is stored in internal common blocks and an " IRA identifier" is returned which can be passed to other IRA routines to refer to the stored astrometry information. This identifier should be annulled when it is no longer required by calling IRA_ANNUL. In addition, a call to IRA_EXPRT may optionally be made to store the astrometry information in an NDF (see argument INDF).

The projection used is specified by the argument PROJ, and must be one of the supported projection types (see routine IRA_IPROJ). For more information on the available projections, see the ID/2 appendix " Projection Equations" . Each projection requires the values for several parameters to be supplied in argument P. These parameters have the same meaning for all projections (for further details see ID/2 appendix " Projection Equations" ):

P(1): The longitude (in the Sky Coordinate System specified by argument SCS) of the reference point in radians.

P(2): The latitude (in the Sky Coordinate System specified by argument SCS) of the reference point in radians.

P(3): The first image coordinate (i.e. X value) of the reference point. Image coordinates are fractional values in which the centre of the pixel (1,1) has coordinates (0.5,0.5).

P(4): The second image coordinate (i.e. Y value) of the reference point.

P(5): The size along the X image axis, of a pixel centred at the reference point, in radians. Actual pixel size will vary over the image due to the distorting effect of the projection. The absolute value is used.

P(6): The size along the Y image axis, of a pixel centred at the reference point, in radians. The absolute value is used.

P(7): The position angle of the Y image axis, in radians. That is, the angle from north to the positive direction of the Y image axis, measured positive in the same sense as rotation from north to east. (Here " north" and " east" are defined by the value of SCS). The X image axis is 90 degrees west of the Y axis.

P(8): An angle through which the celestial sphere is to be rotated before doing the projection. The axis of the rotation is a radius passing through the reference point. The rotation is in an anti-clockwise sense when looking from the reference point towards the centre of the celestial sphere. The value should be in radians. Changing this angle does not change the orientation of the image axes with respect to north (which is set by p(7)).

Invocation

CALL IRA_CREAT( PROJ, NP, P, SCS, EPOCH, INDF, IDA, STATUS )

Arguments

PROJ = CHARACTER ∗ ( ∗ ) (Given)
The projection type (see routine IRA_IPROJ for a list of currently recognised values). Any unambiguous abbreviation can be given.
NP = INTEGER (Given)
The size of array P.
P( NP ) = DOUBLE PRECISION (Given)
The parameter values required by the projection.
SCS = CHARACTER ∗ ( ∗ ) (Given)
The name of the Sky Coordinate System which the projection is to create, or an unambiguous abbreviation. See routine IRA_ISCS for a list of currently recognised values. See ID2 section " Sky Coordinates" ) for general information of Sky Coordinate Systems.
EPOCH = DOUBLE PRECISION (Given)
The Julian epoch at which the observations were made. A single mean epoch is sufficient to describe all IRAS observations. Such a value is contained in the IRA constant IRA__IRJEP.
INDF = INTEGER (Given)
The identifier for the NDF in which the astrometry information is to be stored. If an invalid NDF identifier is given (eg the value NDF__NOID) then the astrometry information is not stored in an NDF (but IDA can still be used to refer to the astrometry information).
IDA = INTEGER (Returned)
The returned IRA identifier.
STATUS = INTEGER (Given and Returned)
The global status.