[VARIANT] = `SIMPLE'

Table: Components of $<$ARRAY$>$ Structure, [VARIANT] = `SIMPLE'

Component Name	TYPE	Brief Description
[VARIANT]	$<$_CHAR$>$	`SIMPLE'
[ORIGIN(NAXIS)]	$<$integer$>$	origin of the data array
[DATA]	$<$narray$>$	actual value at every pixel

[ORIGIN]

The pixel origin in each dimension. If this object is not present, each origin is assumed to be 1. Note that this ability, though present in FORTRAN77, is absent from HDS per se.

This information may be communicated to access routines via the upper and lower bounds on each array dimension, so that the Fortran dimensions would be

    ARRAY(ORIGIN(1):DIMS(1)+ORIGIN(1)-1, ORIGIN(2):DIMS(2)+ORIGIN(2)-1, ...).

[ORIGIN] overcomes a number of quite serious problems, including the old chestnut ``does the first pixel start at (1,1) or (0,0)?'', because the origin is specified explicitly. Also negative pixel indices become available, and therefore an application is freed from having every array co-located at the first pixel, and it may extend arrays in any direction. This property is particularly useful for storing data which require negative indices for a natural representation, such as Fourier-transform data, where zero often needs to be in the centre of the array; or image data after (say) rotation about any point. Storing a pixel origin also enable applications to cut out parts of a data array yet maintain the array's coordinate system (it can be re-combined with the original if necessary). Since the coordinate system is preserved, all the axis scaling is also preserved. This means, for instance, that applications do not have to re-compute the polynomial coefficients in an $<$AXIS$>$ structure when the array size is changed.

NAXIS

The number of axes in the array being represented.

[DATA]

This mandatory item is the NAXIS-dimensional array of numbers.