helper function to select the appropriate interpolator class

    returns interpolator class and keyword arguments for the class

def _get_interpolator_nd(method, **kwargs):
    '''helper function to select the appropriate interpolator class

    returns interpolator class and keyword arguments for the class
    '''
    valid_methods = ['linear', 'nearest']

    try:
        from scipy import interpolate
    except ImportError:
        raise ImportError(
            'Interpolation with method `%s` requires scipy' % method)

    if method in valid_methods:
        kwargs.update(method=method)
        interp_class = interpolate.interpn
    else:
        raise ValueError('%s is not a valid interpolator for interpolating '
                         'over multiple dimensions.' % method)

    return interp_class, kwargs