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
astOutline
X
by an appropriate 1- or 2-character type code. For example, if you
are procesing data with type
"float", you should use the function astOutlineF
(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. Fortran array indexing is used).
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 (assuming the
index "j" to be zero-based). 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".
AST A Library for Handling World Coordinate Systems in Astronomy