Describing observations using XMLΒΆ

Observations can be described in GammaLib using an ASCII file in XML format. The general format of this file is

<observation_list title="observation library">
  <observation name="..." id="..." instrument="...">
    ...
  </observation>
  <observation name="..." id="..." instrument="...">
    ...
  </observation>
  ...
</observation_list>

where each <observation> tag describes one observation. Each observation has a name attribute, an id (identifier) attribute and an instrument attribute. The latter decides which instrument specific class will be allocated upon reading the XML file. For a given instrument, observation identifiers must be unique.

The specific format of the XML file for a given instrument is defined by the relevant instrument specific GObservation class. For example, a CTA observation implemented by the GCTAObservation class is described by

<observation name="..." id="..." instrument="...">
  <parameter name="EventList"           file="..."/>
  <parameter name="EffectiveArea"       file="..."/>
  <parameter name="PointSpreadFunction" file="..."/>
  <parameter name="EnergyDispersion"    file="..."/>
</observation>

for an unbinned observation and by

<observation name="..." id="..." instrument="...">
  <parameter name="CountsCube"          file="..."/>
  <parameter name="EffectiveArea"       file="..."/>
  <parameter name="PointSpreadFunction" file="..."/>
  <parameter name="EnergyDispersion"    file="..."/>
</observation>

for a binned observation. Here, EventList specifies a FITS file containing an event list and CountsCube specifies a FITS file containing a counts cube. The other tags specify the components of the instrumental response function and are optional. Similar definitions exist for the other instruments.

The code threads below show different variants of how observations can be loaded from or saved into an XML file.

C++

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GObservations obs("my_observations.xml");                // Construct observations from XML file
obs.save("my_copied_observations.xml");                  // Save observations into XML file

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GObservations obs;                                       // Construct empty observations
obs.load("my_observations.xml");                         // Load observations from XML file
obs.save("my_copied_observations.xml");                  // Save observations into XML file

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GObservations obs;                                       // Construct empty observations
GXml          xmlin("my_observations.xml");              // Construct GXml instance from XML file
GXml          xmlout;                                    // Construct empty GXml instance
obs.read(xmlin);                                         // Read observations from GXml instance
obs.write(xmlout);                                       // Write observations into GXml instance
xmlout.save("my_copied_observations.xml");               // Save GXml instance in XML file

Python

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obs = gammalib.GObservations('my_observations.xml')  # Construct observations from XML file
obs.save('my_copied_observations.xml')               # Save observations into XML file

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obs = gammalib.GObservations()                       # Construct empty observations
obs.load('my_observations.xml')                      # Load observations from XML file
obs.save('my_copied_observations.xml')               # Save observations into XML file

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obs    = gammalib.GObservations()                    # Construct empty observations
xmlin  = gammalib.GXml('my_observations.xml')        # Construct GXml instance from XML file
xmlout = gammalib.GXml()                             # Construct empty GXml instance
obs.read(xmlin)                                      # Read observations from GXml instance
obs.write(xmlout)                                    # Write observations into GXml instance
xmlout.save('my_copied_observations.xml')            # Save GXml instance in XML file