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StcsArea - Return the CoordinateArea component when reading an STC-S document?

Description:
This is a boolean attribute which controls what is returned by the AST_READ function when it is used to read from an StcsChan. If StcsArea is set non-zero (the default), then a Region representing the STC CoordinateArea will be returned by AST_READ. If StcsArea is set to zero, then the STC CoordinateArea will not be returned.
Type:
Integer (boolean).
Class Applicability:
StcsChan
All StcsChans have this attribute.
Notes:
  • Other attributes such as StcsCoords and StcsProps can be used to specify other Objects to be returned by AST_READ. If more than one of these attributes is set non-zero, then the actual Object returned by AST_READ will be a KeyMap, containing the requested Objects. In this case, the Region representing the STC CoordinateArea will be stored in the returned KeyMap using the key "AREA". If StcsArea is the only attribute to be set non-zero, then the Object returned by AST_READ will be the CoordinateArea Region itself.

  • The class of Region used to represent the CoordinateArea for each STC-S sub-phrase is determined by the first word in the sub-phrase (the "sub-phrase identifier"). The individual sub-phrase Regions are combined into a single Prism, which is then simplified using AST_SIMPLIFY to form the returned region.

  • Sub-phrases that represent a single value ( that is, have identifiers "Time", "Position", "Spectral" or "Redshift" ) are considered to be be part of the STC CoordinateArea component.

  • The TimeFrame used to represent a time STC-S sub-phrase will have its TimeOrigin attribute set to the sub-phrase start time. If no start time is specified by the sub-phrase, then the stop time will be used instead. If no stop time is specified by the sub-phrase, then the single time value specified in the sub-phrase will be used instead. Subsequently clearing the TimeOrigin attribute (or setting its value to zero) will cause the TimeFrame to reprsent absolute times.

  • The Epoch attribute for the returned Region is set in the same way as the TimeOrigin attribute (see above).


next up previous 264
Next: StcsCoords - Return the Coordinates component when reading an STC-S document?
Up: AST Attribute Descriptions
Previous: SpecVal - The spectral position at which flux values are measured

AST A Library for Handling World Coordinate Systems in Astronomy
Starlink User Note 210
R.F. Warren-Smith & D.S. Berry
24th May 2011
E-mail:ussc@star.rl.ac.uk

Copyright (C) 2009 Science \& Technology Facilities Council