This attribute is a boolean value which
specifies how SIP keywords should be handled when reading a FITS-WCS encoded header using the
AST_READ function. See http://irsa.ipac.caltech.edu/data/SPITZER/docs/files/spitzer/shupeADASS.pdf
for more information about SIP headers. If SipReplace is non-zero, then any SIP keywords describing
the inverse transformation (i.e. from WCS to pixel coordinates) are ignored. Instead a new inverse
transformation is found by performing a fit to the forward transformation. The SipReplace attribute
can be set to zero to prevent this happening. If SipReplace is zero, any SIP keywords describing the
inverse transformation are used as supplied, rather than being replaced using a new fit. The default
value is 1.