Extension plugins for reconstruction
====================================

The need of the various reconstruction programs used to create e.g. tracks
from hits may differ significantly and may require different helper data
to perform the required functions.
In general the reconstruction is supported by the detector elements with
helper objects (in DD4hep speak these are called Views). Some default views 
are provided by this package for some of the detector constructors of the 
"default subdetector palette".
We first show how to invoke these plugins in order to attach the required 
extension object and then briefly discuss the plugin palette and it's 
applicability to the various detector constructor types.

Invokation of Extension Plugins
===============================

To add DetElement extensions simply add the corresponding plugin.
This could be performed either by loading a seperate lccdd XML from the 
command line/python interface or adding the corrsponding structures directly
into the primary lccdd file:

<lccdd ..../>
  ....
  <plugins>
    <plugin name="....plugin name.....">
      <argument value="......subdetector name......"/>
      ....
      <argument value="......another subdetector name......"/>
    </plugin>
    ....
  </plugins>
  ....
</lccdd>



Available plugins
=================

-- "SubdetectorExtensionPlugin"
   argument: subdetector name as registered to LCDD
   Adds an extension of type DD4hep::DDRec::SubdetectorExtension.
   Please see documentation in DDRec for details.
   In general applicable to any top level detector object.

-- "LayeringExtensionPlugin"
   argument: subdetector name as registered to LCDD
   Adds an extension of the interface type DD4hep::DDRec::LayeringExtension
   and the implementation type DD4hep::DDRec::LayeringExtensionImpl.
   Please see documentation in DDRec for details.

-- "DD4hep_SiTrackerBarrelSurfacePlugin"
   argument: subdetector name as registered to LCDD
   This plugin adds measurement surfaces of interface type DDSurfaces::ISurface
   to each detector element which has a placement with a sensitive volume.

   Applicable to all instances of type [list to be maintained!]:
    - PolyhedraBarrelCalorimeter2  
    - SiTrackerBarrel
    - EcalBarrel

-- "DD4hep_SiTrackerEndcapSurfacePlugin"
   argument: subdetector name as registered to LCDD
   This plugin adds measurement surfaces of interface type DDSurfaces::ISurface
   to each detector element which has a placement with a sensitive volume.

   Applicable to all instances of type [list to be maintained!]:
    - SiTrackerEndcap2