We have already seen () how the boolean
(integer) Report attribute of a Mapping works. If it is non-zero, the
operation of transforming a set of coordinates will result in a report
being written to standard output. This will display the coordinate
values before and after transformation. It can save considerable time
during program development by eliminating the need to add loops and
output statements to your program.
In a finished program, however, you should be careful that the Report
attribute is not set to a non-zero value unless you want to see the
output (there may often be rather a lot of this!). To help prevent
unwanted output being produced by accident, the Report attribute is
unusual in that its value is not preserved when a Mapping is copied
using astCopy (). Instead, it reverts to its
default of zero (i.e. un-set) in the copy. It also reverts to
zero when a Mapping is written out, e.g. to a file using a
Channel (
).
AST A Library for Handling World Coordinate Systems in Astronomy