Fixed origin position of surface for SiTrackerBarrel_surfaces plugin

DDDetectors/src/SiTrackerBarrel_surfaces.cpp

@@ -27,7 +27,8 @@ void Installer<UserData>::install(DetElement component, PlacedVolume pv)   {
       double sensitive_z_position  = trans[2];
       double outer_thickness = half_module_thickness + sensitive_z_position;
       double inner_thickness = half_module_thickness - sensitive_z_position;
-      Vector3D u(1.,0.,0.), v(0.,1.,0.), n(0.,0.,1.), o(0.,0.,sensitive_z_position);
+      //Surface is placed at the center of the volume, no need to shift origin
+      Vector3D u(1.,0.,0.), v(0.,1.,0.), n(0.,0.,1.), o(0.,0.,0.);
 
       VolPlane surf(comp_vol,Type(Type::Sensitive,Type::Measurement1D),
 		    inner_thickness, outer_thickness, u, v, n, o);