AST_BOX

Create a Box

Description:

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

The Box class implements a Region which represents a box with sides parallel to the axes of a Frame (i.e. an area which encloses a given range of values on each axis). A Box is similar to an Interval, the only real difference being that the Interval class allows some axis limits to be unspecified. Note, a Box will only look like a box if the Frame geometry is approximately flat. For instance, a Box centred close to a pole in a SkyFrame will look more like a fan than a box (the Polygon class can be used to create a box-like region close to a pole).

Invocation

RESULT = AST_BOX( FRAME, FORM, POINT1, POINT2, 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.
FORM = INTEGER (Given)
Indicates how the box is described by the remaining parameters. A value of zero indicates that the box is specified by a centre position and a corner position. A value of one indicates that the box is specified by a two opposite corner positions.
POINT1( ∗ ) = DOUBLE PRECISION (Given)
An array with one element for each Frame axis (Naxes attribute). If FORM is zero, this array should contain the coordinates at the centre of the box. If FORM is one, it should contain the coordinates at the corner of the box which is diagonally opposite the corner specified by POINT2.
POINT2( ∗ ) = DOUBLE PRECISION (Given)
An array with one element for each Frame axis (Naxes attribute) containing the coordinates at any corner of the box.
UNC = INTEGER (Given)
An optional pointer to an existing Region which specifies the uncertainties associated with the boundary of the Box being created. The uncertainty in any point on the boundary of the Box is found by shifting the supplied " uncertainty" Region so that it is centred at the boundary point being considered. The area covered by the shifted uncertainty Region then represents the uncertainty in the boundary 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 Box. Alternatively, a null Object pointer (AST__NULL) may be supplied, in which case a default uncertainty is used equivalent to a box 1.0E-6 of the size of the Box being created.

The uncertainty Region has two uses: 1) when the AST_OVERLAP function compares two Regions for equality the uncertainty Region is used to determine the tolerance on the comparison, and 2) when a Region is mapped into a different coordinate system and subsequently simplified (using AST_SIMPLIFY), the uncertainties are used to determine if the transformed boundary can be accurately represented by a specific shape of Region.

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

Returned Value

AST_BOX = INTEGER
A pointer to the new Box.

Notes:

Status Handling

The protected interface to this function includes an extra parameter at the end of the parameter list descirbed above. This parameter is a pointer to the integer inherited status variable: " int ∗status" .
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