Match the pixel-index bounds of a pair of NDFs
’
PAD’
or ’
TRIM’
(see the Notes section for details). Its value may be abbreviated to 3 characters. If OPTION=’
PAD’
is specified, then the NDF bounds will be matched by "
padding"
; i.e. each NDF
will be extended by selecting the smallest section from it which encompasses all the pixels in
both NDFs. In effect, the pixel-index bounds of the two NDFs are "
maximised"
and the
"
union"
of the two sets of pixels is selected. Any new pixels introduced into either NDF
will be padded with the "
bad"
value. If the NDFs have different numbers of dimensions,
then the dimensionality of both the returned sections will match the NDF with the higher
dimensionality.
If OPTION=’
TRIM’
is specified, then the NDF bounds will be matched by "
trimming"
; i.e. each NDF
will be restricted in extent by selecting a section from it which encompasses only those pixels
which are present in both NDFs. In effect, the pixel-index bounds of the two NDFs are
"
minimised"
and the "
intersection"
of the two sets of pixels is selected. An error will result if the
two NDFs have no pixels in common. If the NDFs have different numbers of dimensions,
then the dimensionality of both the returned sections will match the NDF with the lower
dimensionality.
Note that the initial NDF identifier values will be annulled by this routine and replaced with identifiers describing appropriate new sections from the original NDFs. If access to the original data is still required, then the initial identifiers may be cloned with the routine NDF_CLONE before calling this routine.