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
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.