LSSTApplications
20.0.0
LSSTDataManagementBasePackage
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System for formatting Objects as XML. (string)
This attribute specifies the formatting system to use when AST Objects are written out as XML through an XmlChan. It affects the behaviour of the astWrite function when they are used to transfer any AST Object to or from an external XML representation.
The XmlChan class allows AST objects to be represented in the form of XML in several ways (conventions) and the XmlFormat attribute is used to specify which of these should be used. The formatting options available are outlined in the "Formats Available" section below.
By default, an XmlChan will attempt to determine which format system is already in use, and will set the default XmlFormat value accordingly (so that subsequent I/O operations adopt the same conventions). It does this by looking for certain critical items which only occur in particular formats. For details of how this works, see the "Choice of Default Format" section below. If you wish to ensure that a particular format system is used, independently of any XML already read, you should set an explicit XmlFormat value yourself.
The XmlFormat attribute can take any of the following (case insensitive) string values to select the corresponding formatting system:
If the XmlFormat attribute of an XmlChan is not set, the default value it takes is determined by the presence of certain critical items within the document most recently read using Channel::read. The sequence of decision used to arrive at the default value is as follows:
QUOTED
.Setting an explicit value for the XmlFormat attribute always over-rides this default behaviour.
The "IVOA" support caters only for certain parts of V1.20 of the draft Space-Time Coordinate (STC) schema (see http://www.ivoa.net/Documents/WD/STC/STC-20050225.html). Note, this draft has now been superceded by an officially adopted version that differs in several significant respects from V1.20. Consequently, the "IVOA" XmlChan format is of historical interest only.
The following points should be noted when using an XmlChan to read or write STC information (note, this list is currently incomplete):
<STCMetadata>
element will be an instance of one of the AST "Stc" classes: StcResourceProfile, StcSearchLocation, StcCatalogEntryLocation, StcObsDataLocation.<STCMetadata>
element, the axes in the returned AST Object will be in the order space, time, spectral, redshift, irrespective of the order in which the axes occur in the <STCMetadata>
element. If the supplied <STCMetadata>
element does not contain all of these axes, the returned AST Object will also omit them, but the ordering of those axes which are present will be as stated above. If the spatial frame represents a celestial coordinate system the spatial axes will be in the order (longitude, latitude).<TimeFrame>
element. Consequently, most of the information within a <TimeFrame>
element is currently ignored.<SpaceFrame>
elements can only be read if they describe a celestial longitude and latitude axes supported by the AST SkyFrame class. The space axes will be returned in the order (longitude, latitude).<GenericCoordFrame> elements within an <AstroCoordSystem>
element are currently ignored.<AstroCoordSystem>
found within an STCMetaData element is ignored.<AstroCoordArea>
found within an STCMetaData element is ignored.<OffsetCenter> found within a <SpaceFrame>
is ignored.<SpaceFrame>
is ignored.<SpaceFrame>
elements can only be read if they refer to one of the following space reference frames: ICRS, GALACTIC_II, SUPER_GALACTIC, HEE, FK4, FK5, ECLIPTIC.<SpaceFrame>
elements can only be read if the reference position is TOPOCENTER. Also, any planetary ephemeris is ignored.<RegionFile>
elements are not supported.<Polygon>
elements are always considered to be joined using great circles (that is, <SmallCircle>
elements are ignored).Controls output buffer length. (int)
This attribute specifies the maximum length to use when writing out text through the sink function supplied when the XmlChan was created.
The number of characters in each string written out through the sink function will not be greater than the value of this attribute (but may be less). A value of zero (the default) means there is no limit - each string can be of any length.
The namespace prefix to use when writing. (string)
This attribute is a string which is to be used as the namespace prefix for all XML elements created as a result of writing an AST Object out through an XmlChan. The URI associated with the namespace prefix is given by the symbolic constant AST__XMLNS
defined in ast.h
. A definition of the namespace prefix is included in each top-level element produced by the XmlChan.
The default value is a blank string which causes no prefix to be used. In this case each top-level element will set the default namespace to be the value of AST__XMLNS
.