def __init__(self, ds, start_point, end_point, npoints, label=None):
    self.ds = ds
    self.start_point = _validate_point(start_point, ds, start=True)
    self.end_point = _validate_point(end_point, ds)
    self.npoints = npoints
    self.label = label
    self.data = {}
def __init__(self, ds, start_point, end_point, npoints, label=None):
    self.ds = ds
    self.start_point = _validate_point(start_point, ds, start=True)
    self.end_point = _validate_point(end_point, ds)
    self.npoints = npoints
    self.label = label
    self.data = {}