If an integer axis index is included in the attribute name (e.g.
" ) then
the attribute value should be supplied as a single floating point axis value, in
radians, when setting a value for the attribute, and will be returned in the same form
when getting the value of the attribute. In this case the integer axis index should be
" (the values to use for longitude and latitude axes are given by the
LonAxis and LatAxis attributes).
If no axis index is included in the attribute name (e.g.
" ) then the
attribute value should be supplied as a character string containing two formatted axis
values (an axis 1 value followed by a comma, followed by an axis 2 value). The same
form will be used when getting the value of the attribute.
If the position given by the SkyRef attribute defines the origin of the offset
coordinate system (that is, if the SkyRefIs attribute is set to
" ), then there
will in general be two orientations which will put the supplied SkyRefP position on the
zero longitude meridian. The orientation which is actually used is the one which
gives the SkyRefP position a positive latitude in the offset coordinate system
(the other possible orientation would give the SkyRefP position a negative
An error will be reported if an attempt is made to use a SkyRefP value which is co-incident with SkyRef or with the point diametrically opposite to SkyRef on the celestial sphere. The reporting of this error is deferred until the SkyRef and SkyRefP attribute values are used within a calculation.
If the System attribute of the SkyFrame is changed, any position given for SkyRefP is transformed into the new System.