This attribute is used to control the orientation of the offset
coordinate system defined by attributes SkyRef and SkyRefIsSkyRefIs. If used,
it should be set to hold the longitude and latitude of a point within
the coordinate system specified by the SystemSystem attribute. The offset
coordinate system represented by the SkyFrameSkyFrame will then be rotated in
order to put the position supplied for SkyRefP on the zero longitude
meridian. This rotation is about an axis from the centre of the
celestial sphere to the point specified by the SkyRef attribute.
The default value for SkyRefP is usually the north pole (that is, a
latitude of
90 degrees in the coordinate system specified by the System
attribute). The exception to this is if the SkyRef attribute is
itself set to either the north or south pole. In these cases the
default for SkyRefP is the origin (that is, a (0,0) in the coordinate
system specified by the System attribute).
If an integer axis index is included in the attribute name (e.g.
"SkyRefP(1)") 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 "1"
or "2" (the values to use for longitude and latitude axes are
given by the LonAxisLonAxis and LatAxisLatAxis attributes).
If no axis index is included in the attribute name (e.g. "SkyRefP") 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.