def nextID_in_poly(poly, id):
    """
    Determines the id of the next point on a standard polygon.

    Parameters
    ----------
    poly :: List of (x,y) tuples
        Representation of a polygon, with identical first and last vertices.
    id : Integer

    Returns
    -------
    Integer

    """
    if id==len(poly)-1:
        return 1
    elif id== len(poly)-2:
        return 0
    else:
        return id+1