MCParticle Endpoint bit treatment differs from LCIO

[fdplacido]

• Package version: v00-03-01

MCParticle on LCIO treats the Endpoint status bit differently to EDM4hep.
EDM4hep doesn't provide a way to change this bit either (unless setting all the SimulatorStatus bits at once with an int).

For example, setting the Endpoint in LCIO will change that bit, but EDM4hep won't.

void MCParticleImpl::setEndpoint( const double endpoint[3] ){
  _simstatus.set( BITEndpoint ) ;
  _endpoint[0] = endpoint[0] ;                                                                                                                                                                   
  _endpoint[1] = endpoint[1] ;                                                                                                                                                                   
  _endpoint[2] = endpoint[2] ;
}

On getting the Endpoint a special treatment is applied depending on the value of that bit, wheras just the endpoint array is returned in EDM4hep.

  const double* MCParticleImpl::getEndpoint() const {
    if( ! _simstatus.test( BITEndpoint  ) ){
      if( _daughters.size() == 0 ) return  _endpoint ;

      for(unsigned int i=0;i<_daughters.size();i++)
      {
          if(!_daughters[i]->vertexIsNotEndpointOfParent())
          return _daughters[i]->getVertex();
      }
      return _endpoint ;
    } else
      return _endpoint ;
  } 

[gaede]

This is a very special case in LCIO. The bit BITEndpoint is used to decide whether the endpoint of the MCParticle has been set by the user and only then writes it to the file. In PODIO the endpoint is written unconditionally and therefore this bit is not needed and likewise the logic for returning the first daughters vertex in case the bit is not set is not strictly needed here. However it is the users responsibility to ensure that the endpoint is set consistently with that of decay daughters. In general, if we really need to keep internal state of objects consistent, we should provide suitable utility methods to do so. Should remove the BITEndpoint from EDM4hep.