A basic 2-dimensional Frame is used to represent the pixel coordinate system in the returned Polygon. The Domain attribute is set to "PIXEL", the Title attribute is set to "Pixel coordinates", and the Unit attribute for each axis is set to "pixel". All other attributes are left unset. The nature of the pixel coordinate system is determined by parameter STARPIX.
The MAXERR and MAXVERT parameters can be used to control how accurately the returned Polygon represents the required region in the data array. The number of vertices in the returned Polygon will be the minimum needed to achieve the required accuracy.
You should use a function which matches the numerical type of the data you are processing by replacing X in the generic function name AST_OUTLINEX are procesing data with type REAL, you should use the function AST_OUTLINER (see the "Data Type Codes" section below for the codes appropriate to other numerical types).
The storage order of data within this array should be such that the index of the first grid dimension varies most rapidly and that of the second dimension least rapidly (i.e. normal Fortran array storage order).
Note that LBND and UBND together define the shape and size of the input grid, its extent along a particular (J'th) dimension being UBND(J)-LBND(J)1. They also define the input grid's coordinate system, each pixel having unit extent along each dimension with integral coordinate values at its centre or upper corner, as selected by parameter STARPIX.
For compatibility with other Starlink facilities, the codes W and UW are provided as synonyms for S and US respectively (but only in the Fortran interface to AST).
AST A Library for Handling World Coordinate Systems in Astronomy