This function creates a new
Circle and optionally
initialises its attributes.
A Circle is a Region which represents a circle or sphere within the supplied Frame.
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 circle is described by the remaining parameters. A value of zero indicates that the
circle is specified by a centre position and a position on the circumference. A value of one
indicates that the circle is specified by a centre position and a scalar radius.
CENTRE(
∗ ) =
DOUBLE PRECISION (Given)
An array with one element for each Frame axis (
Naxes
attribute) containing the coordinates at the centre of the circle or sphere.
POINT(
∗ ) =
DOUBLE PRECISION (Given)
If FORM is zero, then this array should have one element for each
Frame axis (Naxes attribute), and should be supplied holding the coordinates at a point on
the circumference of the circle or sphere. If FORM is one, then this array should have one
element only which should be supplied holding the scalar radius of the circle or sphere, as a
geodesic distance within the Frame.
UNC = INTEGER (Given)
An optional pointer to
an existing Region which specifies the uncertainties associated with the boundary of the
Circle being created. The uncertainty in any point on the boundary of the Circle 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 Circle. 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 Circle 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 Circle. The syntax used is identical to that for the
AST_SET routine.
STATUS = INTEGER (Given and Returned)
The global status.