AST_NULLREGION

Create a NullRegion

Description:

This function creates a new NullRegion and optionally initialises its attributes.

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.

Invocation

RESULT = AST_NULLREGION( FRAME, UNC, OPTIONS, STATUS )

Arguments

FRAME = INTEGER (Given)
A pointer to the Frame in which the region is defined. A deep copy is taken of the supplied Frame. This means that any subsequent changes made to the Frame using the supplied pointer will have no effect the Region.
UNC = INTEGER (Given)
An optional pointer to an existing Region which specifies the uncertainties associated with positions in the supplied Frame. The uncertainty in any point in the Frame is found by shifting the supplied " uncertainty" 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.

OPTIONS = CHARACTER ( ) (Given)
A character string containing an optional comma-separated list of attribute assignments to be used for initialising the new NullRegion. The syntax used is identical to that for the AST_SET routine.
STATUS = INTEGER (Given and Returned)
The global status.

Returned Value

AST_NULLREGION = INTEGER
A pointer to the new NullRegion.

Notes: