All sub-classes of Region require a Frame to be supplied when the Region is created.
This Frame describes the coordinate system in which the Region is defined, and is
referred to as the
" encapsulated Frame
" below. Constructors will also typically
required one or more positions to be supplied which define the location and
extent of the region. These positions must be supplied within the encapsulated
The Region class inherits from the Frame class, and so a Region can be supplied where-ever a Frame is expected. In these cases, supplying a Region is equivalent to supplying a reference to its encapsulated Frame. Thus all the methods of the Frame class can be used on the Region class. For instance, the astFormat function may be used on a Region to format an axis value.
In addition, since Frame inherits from Mapping, a Region is also a sort
of Mapping. Transforming positions by supplying a Region to one of the
functions is the way to determine if a given position is inside or outside the Region.
When used as a Mapping, most classes of Frame are equivalent to a UnitMap.
However, the Region class modifies this behaviour so that a Region acts like a
UnitMap only for input positions which are within the area represented by the
Region. Input positions which are outside the area produce bad output values
(i.e. the output values are equal to AST__BAD). This behaviour is the same for
both the forward and the inverse transformation. In this sense the
" is not a true inverse of the forward transformation, since
applying the forward transformation to a point outside the Region, and then
applying the inverse transformation results, in a set of AST__BAD axis values
rather than the original axis values. If required, the astRemoveRegions function
can be used to remove the
" effect of any Regions contained within a
compound Mapping or FrameSet. It does this by replacing each Region with a
UnitMap or equivalent Frame (depending on the context in which the Region is
If the coordinate system represented by the Region is changed (by changing the values
of one or more of the attribute which the Region inherits from its encapsulated Frame),
the area represented by the Region is mapped into the new coordinate system. For
’ s say a Circle (a subclass of Region) is created, a SkyFrame being
supplied to the constructor so that the Circle describes a circular area on the sky in
FK4 equatorial coordinates. Since Region inherits from Frame, the Circle will have
a System attribute and this attribute will be set to
" . If the System
attribute of the Region is then changed from FK4 to FK5, the circular area
represented by the Region will automatically be mapped from the FK4 system into
the FK5 system. In general, changing the coordinate system in this way may
result in the region changing shape - for instance, a circle may change into an
ellipse if the transformation from the old to the new coordinate system is
linear but with different scales on each axis. Thus the specific class of a
Region cannot be used as a guarantee of the shape in any particular coordinate
system. If the astSimplify function is used on a Region, it will endeavour
to return a new Region of a sub-class which accurately describes the shape
in the current coordinate system of the Region (but this may not always be
It is possible to negate an existing Region so that it represents all areas of the encapsulated Frame except for the area specified when the Region was created.
Adaptive: Should the area adapt to changes in the coordinate system?
Negated: Has the original region been negated?
Closed: Should the boundary be considered to be inside the region?
MeshSize: Number of points used to create a mesh covering the Region
FillFactor: Fraction of the Region which is of interest
Bounded: Is the Region bounded?
Every Region also inherits any further attributes that belong to the encapsulated
Frame, regardless of that Frame
’ s class. (For example, the Equinox attribute, defined
by the SkyFrame class, is inherited by any Region which represents a SkyFrame.)
astGetRegionBounds: Get the bounds of a box containing a Region
astGetRegionFrame: Get a copy of the Frame represent by a Region
astGetRegionFrameSet: Get a copy of the Frameset encapsulated by a Region
astGetRegionMesh: Get a mesh of points covering a Region
astGetRegionPoints: Get the positions that define a Region
astGetUnc: Obtain uncertainty information from a Region
astGetRegionDisc: Get the bounds of disc containing a Region
astMapRegion: Transform a Region into a new coordinate system
astNegate: Toggle the value of the Negated attribute
astOverlap: Determines the nature of the overlap between two Regions
astMaskX: Mask a region of a data grid
astSetUnc: Associate a new uncertainty with a Region
astShowMesh: Display a mesh of points on the surface of a Region