A NullRegion is a Region with no bounds. If the Negated attribute of a NullRegion is false, the NullRegion represents a Region containing no points. If the Negated attribute of a NullRegion is true, the NullRegion represents an infinite Region containing all points within the coordinate system.
"Region so that it is centred at the point being considered. The area covered by the shifted uncertainty Region then represents the uncertainty in the position. The uncertainty is assumed to be the same for all points.
If supplied, the uncertainty Region must be of a class for which all instances are centro-symetric (e.g. Box, Circle, Ellipse, etc.) or be a Prism containing centro-symetric component Regions. A deep copy of the supplied Region will be taken, so subsequent changes to the uncertainty Region using the supplied pointer will have no effect on the created NullRegion. Alternatively, a null Object pointer (AST__NULL) may be supplied, in which case a default uncertainty of zero is used.
A null Object pointer (AST__NULL) will be returned if this function is invoked with STATUS set to an error value, or if it should fail for any reason.