@abstractmethod<EOL><INDENT>def _augment_keypoints(self, keypoints_on_images, random_state, parents, hooks):<DEDENT>
raise NotImplementedError()<EOL>
Augment keypoints on multiple images.

This is the internal variation of ``augment_keypoints()``.
It is called from ``augment_keypoints()`` and should usually not be
called directly. It has to be implemented by every augmenter.
This method may transform the keypoints in-place.
This method does not have to care about determinism or the
Augmenter instance's ``random_state`` variable. The parameter
``random_state`` takes care of both of these.

Parameters
----------
keypoints_on_images : list of imgaug.KeypointsOnImage
    Keypoints to augment. They may be changed in-place.

random_state : numpy.random.RandomState
    The random state to use for all sampling tasks during the augmentation.

parents : list of imgaug.augmenters.meta.Augmenter
    See :func:`imgaug.augmenters.meta.Augmenter.augment_keypoints`.

hooks : imgaug.HooksKeypoints or None
    See :func:`imgaug.augmenters.meta.Augmenter.augment_keypoints`.

Returns
----------
list of imgaug.KeypointsOnImage
    The augmented keypoints.