This routine calculates the parameters of a tangent-plane projection that gives an
optimal representation of a set of supplied sky positions. The projection parameters are
the normal FITS CRPIX1/2, CRVAL1/2, CDELT1/2 and CROTA2 keywords. They are
chosen in order to maximise the number of sky positions that fall close to the centre of
a pixel.
NPOS = INTEGER (Given)
The number of sky positions.
POS( 2, NPOS ) =
DOUBLE PRECISION (Given)
The sky positions. These should be (longitude,latitude) values,
in radians, in any celestial co-ordinate system.
WEST = LOGICAL (Given)
If .TRUE.,
then it is assumed that the X grid axis increases westwards (assuming north is parallel to
ve Y).
This is the case for most celestial co-ordinate systems such as (RA,Dec) etc. If .FALSE.,
then it is assumed that the X grid axis increases eastwards (assuming north is parallel to
ve Y).
This is the case for a few systems such as (az,el) and geographic (longitude,latitude).
PAR( 7 ) =
DOUBLE PRECISION (Given and Returned)
The projection parameters. Each parameter that is
supplied with a value of AST__BAD on entry will be replaced on exit with the optimal value.
Non-bad supplied values will be left unchanged on exit. The supplied values will also be left
unchanged if optimal values cannot be determined. They are stored in the order CRPIX1,
CRPIX2, CRVAL1, CRVAL2, CDELT1, CDELT2, CROTA2. CRPIX1 and CRPIX2 are in units
of pixels. All the other projection parameters will be in units of radians, and refer to the
celestial co-ordinate system in which the POS values are supplied. CROTA2 is the angle from
the Y axis to celestial north, measured north through east (no matter the value of WEST).
Returned pixel sizes are rounded to the nearest tenth of an arcsecond.
RDIAM = DOUBLE
PRECISION (Returned)
The diameter of the circle that just encloses all the supplied sky
positions, in radians.
STATUS = INTEGER (Given and Returned)
The global status.