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Description: 
This function returns a 
Region which represents the uncertainty associated
with positions within the supplied Region. See 
astSetUnc for more
information about Region uncertainties and their use.  
Synopsis 
 AstRegion
astGetUnc(
AstRegion this,
int def )  
 Parameters: 
  this  
 Pointer to the Region.  
  def  
 Controls what is
returned if no uncertainty information has been associated explicitly with the supplied
Region. If a non-zero value is supplied, then the default uncertainty Region used
internally within AST is returned (see " Applicability" below). If zero is supplied,
then NULL will be returned (without error).  
    Applicability 
  The default
uncertainty for a CmpRegion is taken from one of the two component Regions. If the
first component Region has a non-default uncertainty, then it is used as the default
uncertainty for the parent CmpRegion. Otherwise, if the second component Region has a
non-default uncertainty, then it is used as the default uncertainty for the parent
CmpRegion. If neither of the component Regions has non-default uncertainty, then the
default uncertainty for the CmpRegion is 1.0E-6 of the bounding box of the
CmpRegion.  
  The default uncertainty for a Prism is formed by combining
the uncertainties from the two component Regions. If a component Region does
not have a non-default uncertainty, then its default uncertainty will be used
to form the default uncertainty of the parent Prism.  
  Region  
 For other
classes of Region, the default uncertainty is 1.0E-6 of the bounding box of the
Region. If the bounding box has zero width on any axis, then the uncertainty
will be 1.0E-6 of the axis value.  
    Returned Value 
  astGetUnc()  
 A pointer
to a Region describing the uncertainty in the supplied Region.  
    Notes: 
- 
If uncertainty information is associated with a Region, and the coordinate system
described by the Region is subsequently changed (e.g. by changing the value of its
System attribute, or using the astMapRegion function), then the uncertainty information
                                                                                       
                                                                                       
returned by this function will be modified so that it refers to the coordinate system
currently described by the supplied Region.
 
- 
A null Object pointer (NULL) will be returned if this function is invoked with the AST
error status set, or if it should fail for any reason.   
  Copyright (C) 2021 East Asian Observatory
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 A Library for Handling
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Coordinate Systems
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