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LSST Data Management Base Package
Channel Attributes

Channel Attributes

Channel_Comment

Include textual comments in output? (bool)

This is a boolean attribute which controls whether textual comments are to be included in the output generated by a Channel. If included, they will describe what each item of output represents.

If Comment is true, then comments will be included. If it is false, comments will be omitted.

Applicability

Channel_Full

Set level of output detail. (int)

This attribute is a three-state flag and takes values of -1, 0 or +1. It controls the amount of information included in the output generated by a Channel.

If Full is false, then a modest amount of non-essential but useful information will be included in the output. If Full is negative, all non-essential information will be suppressed to minimise the amount of output, while if it is positive, the output will include the maximum amount of detailed information about the Object being written.

Applicability

  • Channel

    The default value is false for a normal Channel.

  • FitsChan

    The default value is false for a FitsChan.

  • XmlChan

    The default value is -1 for an XmlChan.

  • StcsChan

    The default value is false for an StcsChan. Set a positive value to cause default values to be included in STC-S descriptions.

Notes

  • All positive values supplied for this attribute are converted to +1 and all negative values are converted to -1.

Channel_Indent

Specifies the indentation to use in text produced by a Channel. (int)

This attribute controls the indentation within the output text produced by Channel::write. It gives the increase in the indentation for each level in the object heirarchy. If it is set to zero, no indentation will be used.

Applicability

  • Channel

    The default value is zero for a basic Channel.

  • FitsChan

    The FitsChan class ignores this attribute.

  • StcsChan

    The default value for an StcsChan is zero, which causes the entire STC-S description is written out by a single invocation of the sink function. The text supplied to the sink function will not contain any linefeed characters, and each pair of adjacent words will be separated by a single space. The text may thus be arbitrarily large and the StcsLength attribute is ignored.

    If Indent is non-zero, then the text is written out via multiple calls to the sink function, each call corresponding to a single "line" of text (although no line feed characters will be inserted by AST). The complete STC-S description is broken into lines so that:

    • the line length specified by attribute StcsLength is not exceeded
    • each sub-phrase (time, space, etc.) starts on a new line
    • each argument in a compound spatial region starts on a new line

    If this causes a sub-phrase to extend to two or more lines, then the second and subsequent lines will be indented by three spaces compared to the first line. In addition, lines within a compound spatial region will have extra indentation to highlight the nesting produced by the parentheses. Each new level of nesting will be indented by a further three spaces.

  • XmlChan

    The default value for an XmlChan is zero, which results in no linefeeds or indentation strings being added to output text. If any non-zero value is assigned to Indent, then extra linefeed and space characters will be inserted as necessary to ensure that each XML tag starts on a new line, and each tag will be indented by a further 3 spaces to show its depth in the containment hierarchy.

Channel_ReportLevel

Determines which read/write conditions are reported. (int)

This attribute determines which, if any, of the conditions that occur whilst reading or writing an Object should be reported. These conditions will generate either a fatal error or a warning, as determined by attribute Strict. ReportLevel can take any of the following values:

  • 0 - Do not report any conditions.
  • 1 - Report only conditions where significant information content has been changed. For instance, an unsupported time-scale has been replaced by a supported near-equivalent time-scale. Another example is if a basic Channel unexpected encounters data items that may have been introduced by later versions of AST.
  • 2 - Report the above, and in addition report significant default values. For instance, if no time-scale was specified when reading an Object from an external data source, report the default time-scale that is being used.
  • 3 - Report the above, and in addition report any other potentially interesting conditions that have no significant effect on the conversion. For instance, report if a time-scale of "TT" (terrestrial time) is used in place of "ET" (ephemeris time). This change has no signficiant effect because ET is the predecessor of, and is continuous with, TT. Synonyms such as "IAT" and "TAI" are another example.

The default value is 1. Note, there are many other conditions that can occur whilst reading or writing an Object that completely prevent the conversion taking place. Such conditions will always generate errors, irrespective of the ReportLevel and Strict attributes.

Applicability to Subclasses

  • FitsChan

    All the conditions selected by the FitsChan Warnings attribute are reported at level 1.

Channel_Skip

Skip irrelevant data? (bool)

This is a boolean attribute which indicates whether the Object data being read through a Channel are inter-mixed with other, irrelevant, external data.

If Skip is false (the default for all but FitsChan), then the source of input data is expected to contain descriptions of AST Objects and comments and nothing else (if anything else is read, an error will result). If Skip is true (the default for @ref FitsChan), then any non-Object data encountered between Objects will be ignored and simply skipped over in order to reach the next Object.

Applicability to Subclasses

  • FitsChan

    The FitsChan class sets the default value of this attribute to true, so that all irrelevant FITS headers will normally be ignored.

Channel_Strict

Report an error if any unexpeted data items are found? (bool)

This is a boolean attribute which indicates whether a warning rather than an error should be issed for insignificant conversion problems. If it is set true, then fatal errors are issued instead of warnings, resulting in an exception being thrown. If Strict is false (the default), then execution continues after minor conversion problems, and a warning message is added to the Channel structure. Such messages can be retrieved using the astWarnings function.

Notes

  • This attribute was introduced in AST version 5.0. Prior to this version of AST unexpected data items read by a basic Channel always caused an error to be reported. So applications linked against versions of AST prior to version 5.0 may not be able to read Object descriptions created by later versions of AST, if the Object's class description has changed.
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