//  Set up access to the internal velocity field and mesh
    const volVectorField& U =
        db().objectRegistry::lookupObject<volVectorField>(UName_);
    const fvMesh& mesh = patch().boundaryMesh().mesh();

    forAll(patch(), facei)
    {
    // get global cell indices for cells adjacent to patch    
        label celli = patch().faceCells()[facei];

    // get global face indices for faces opposite patch face
    label oppFacei = mesh.cells()[celli].opposingFaceLabel(facei+patch().patch().start(),mesh.faces());

    // get coordinates of center of cell adjacent to patch (patch cells)
    vector cellCentreO = mesh.cellCentres()[mesh.owner()[oppFacei]];

    // get coordinates of center of cell on the side opposite the patch of
    // the patch cell
    vector cellCentreN = mesh.cellCentres()[mesh.neighbour()[oppFacei]];

    // get coordinates of center of face opposite the patch boundary face
    vector faceCentre  = mesh.faceCentres()[oppFacei];

    // get coordinates of center of patch boundary face;
    vector patchFaceCentre = mesh.faceCentres()[facei+patch().patch().start()];
    }