### JSATILEINFO

Return information about a specified sky tile

#### Description:

This routine returns information about a single standard sky tile for a named JCMT instrument (specified by parameter ITILE). This includes the RA and Dec. of the tile centre, the tile size, the tile WCS, and whether the NDF containing the accumulated co-added data for the tile currently exists. If not, there is an option to create it and fill it with zeros (see parameter CREATE). In addition, an NDF can be created containing the tile index at every point on the whole sky (see parameter ALLSKY).

Also, the bounds of the overlap in pixel indices between the tile and a specified NDF or Region can be found (see parameter TARGET).

The environment variable JSA_TILE_DIR should be defined prior to using this command, and should hold the path to the directory in which the NDFs containing the accumulated co-added data for each tile are stored. Tiles for a specified instrument will be stored within a sub-directory of this directory (see parameter INSTRUMENT). If JSA_TILE_DIR is undefined, the current directory is used.

#### Parameters:

##### ALLSKY = NDF (Write)
If not null (!), this is the name of a new 2D NDF to create holding the tile index at every point on the sky. The pixel size in this image is much larger than in an individual tile in order to keep the NDF size managable. Each pixel holds the integer index of a tile. Pixels that have no corresponding tile hold a bad value. [!]
Indicates if the NDF containing co-added data for the tile should be created if it does not already exist. If TRUE, and if the tile’ s NDF does not exist on entry to this command, a new NDF will be created for the tile and filled with zeros. The instrument subdirectory within the JSA_TILE_DIR directory will be created if it does not already exist. [FALSE]
##### DECCEN = _DOUBLE (Write)
An output parameter to which is written the ICRS Declination of the tile centre, in radians.
##### EXISTS = _LOGICAL (Write)
An output parameter that is set TRUE if the NDF containing co-added data for the tile existed on entry to this command (FALSE otherwise).
The name of a new text file in which to store the WCS and extent of the tile in the form of a set of FITS-WCS headers. [!]
The JCMT instrument (different instruments have different tiling schemes and pixel sizes). The following instrument names are recognised (unambiguous abbreviations may be supplied): " SCUBA-2(450)" , " SCUBA-2(850)" , " ACSIS" , " DAS" . NDFs containing co-added data for the selected instrument reside within a corresponding sub-directory of the directory specified by environment variable JSA_TILE_DIR. These sub-directories are called " scuba2-450" , " scuba2-850" , " acsis" and " das" .
The index of the tile about which information is required. The first tile has index 0. The largest allowed tile index is always returned in output parameter MAXTILE. If a null (!) value is supplied for ITILE, the MAXTILE parameter is still written, but the command will then exit immediately without further action (and without error).
##### LBND( 2 ) = _INTEGER (Write)
An output parameter to which are written the lower pixel bounds of the NDF containing the co-added data for the tile.
If TRUE, the FITS reference point is put at the centre of the tile. Otherwise, it is put at RA=0 Dec=0. [FALSE]
##### MAXTILE = _INTEGER (Write)
An output parameter to which is written the largest tile index associated with the instrument specified by parameter INSTRUMENT.
Determines the JSA projection to use. The allowed values are " HPX" (HPX projection centred on RA=0h), " HPX12" (HPX projection centred on RA=12h), " XPHN" (XPH projection centred on the north pole) and " XPHS" (XPH projection centred on the south pole). A null (!) value causes " HPX" to be used. [" HPX" ]
##### RACEN = LITERAL (Write)
An output parameter to which is written the ICRS Right Ascension of the tile centre, in radians.
The name of a new text file in which to store the WCS and extent of the tile in the form of an AST Region. [!]
##### SIZE = _DOUBLE (Write)
An output parameter to which is written the arc-length of each side of a square bounding box for the tile, in radians.