void PndConstField::GetBxyz(const Double_t point[3], Double_t* bField){
  if ( point [0] < fXmin  ||  point [0] > fXmax  ||
       point [1] < fYmin  ||  point [1] > fYmax  ||
       point [2] < fZmin  ||  point [2] > fZmax ) {
    bField[0]=0;     bField[1]=0;    bField[2]=0;
  }
  else{
    bField[0]=fBx;     bField[1]=fBy;    bField[2]=fBz;
  }
}