Always initialize DD4hep geometry in your Marlin analysis

[rete]

Description

• Samples: all
• Benchmark analysis: all
• ILCSoft version: v02-00-01

If you try to run your analysis processor without initializing the geometry before any processor, you won't get any exception with ILCSoft v02-00-01. But it doesn't mean that everything ran correctly. Some processors may need information from the detector geometry, such as the B field. If you try to run the same processors with ILCSoft > v02-00-01, you will get exceptions if you try to access geometry information. Example message when trying to access the B field in this case:

 ***********************************************
 A runtime error occured - (uncaught exception):
      Detector geometry not initialised, cannot get bfield
 Marlin will have to be terminated, sorry.
 ***********************************************

This is due to a change in the DD4hep (version > v01-07-02) and MarlinUtil (version > v01-15) versions, where exceptions are now thrown if the you try to access geometry information but have not initialized it.

Known fix / solution

In order to avoid/fix this problem, always initialize the DD4hep geometry before running any other processor. In your Marlin steering file add this:

<execute>
   <processor name="InitDD4hep"/>
   <!-- Your processors there -->
</execute>
<processor name="InitDD4hep" type="InitializeDD4hep">
    <!--InitializeDD4hep reads a compact xml file and initializes the DD4hep::LCDD object-->
    <!--Name of the DD4hep compact xml file to load-->
    <parameter name="DD4hepXMLFile" type="string"> compact.xml </parameter>
</processor>

and replace compact.xml by the compact geometry file. You can find the detector model in your slcio file by using the dumpevent command on any event like:

dumpevent some_file.slcio 1 | less

and get it from the head:

============================================================================
        Event  : 0 - run:  108598 - timestamp 0 - weight 1
============================================================================
 date:      01.01.1970  00:00:00.000000000
 detector : ILD_l5_v02
 event parameters: 
 parameter BeamPDG0 [int]: 11,
...

The corresponding compact file can be thus found in $lcgeo_DIR/ILD/compact/ILD_l5_v02/ILD_l5_v02.xml in this case.

See also

• Issues:
  • Create check if geometry and field are not empty AIDASoft/DD4hep#361
• Pull request
  • Geom field validity change iLCSoft/MarlinUtil#11
  • Implement issue #361 AIDASoft/DD4hep#367