

.. _sphx_glr_gallery_widgets_polygon_selector_demo.py:


=====================
Polygon Selector Demo
=====================

Shows how one can select indices of a polygon interactively.





.. image:: /gallery/widgets/images/sphx_glr_polygon_selector_demo_001.png
    :align: center


.. rst-class:: sphx-glr-script-out

 Out::

    Select points in the figure by enclosing them within a polygon.
    Press the 'esc' key to start a new polygon.
    Try holding the 'shift' key to move all of the vertices.
    Try holding the 'ctrl' key to move a single vertex.

    Selected points:
    []




|


.. code-block:: python

    import numpy as np

    from matplotlib.widgets import PolygonSelector
    from matplotlib.path import Path


    class SelectFromCollection(object):
        """Select indices from a matplotlib collection using `PolygonSelector`.

        Selected indices are saved in the `ind` attribute. This tool fades out the
        points that are not part of the selection (i.e., reduces their alpha
        values). If your collection has alpha < 1, this tool will permanently
        alter the alpha values.

        Note that this tool selects collection objects based on their *origins*
        (i.e., `offsets`).

        Parameters
        ----------
        ax : :class:`~matplotlib.axes.Axes`
            Axes to interact with.

        collection : :class:`matplotlib.collections.Collection` subclass
            Collection you want to select from.

        alpha_other : 0 <= float <= 1
            To highlight a selection, this tool sets all selected points to an
            alpha value of 1 and non-selected points to `alpha_other`.
        """

        def __init__(self, ax, collection, alpha_other=0.3):
            self.canvas = ax.figure.canvas
            self.collection = collection
            self.alpha_other = alpha_other

            self.xys = collection.get_offsets()
            self.Npts = len(self.xys)

            # Ensure that we have separate colors for each object
            self.fc = collection.get_facecolors()
            if len(self.fc) == 0:
                raise ValueError('Collection must have a facecolor')
            elif len(self.fc) == 1:
                self.fc = np.tile(self.fc, (self.Npts, 1))

            self.poly = PolygonSelector(ax, self.onselect)
            self.ind = []

        def onselect(self, verts):
            path = Path(verts)
            self.ind = np.nonzero(path.contains_points(self.xys))[0]
            self.fc[:, -1] = self.alpha_other
            self.fc[self.ind, -1] = 1
            self.collection.set_facecolors(self.fc)
            self.canvas.draw_idle()

        def disconnect(self):
            self.poly.disconnect_events()
            self.fc[:, -1] = 1
            self.collection.set_facecolors(self.fc)
            self.canvas.draw_idle()


    if __name__ == '__main__':
        import matplotlib.pyplot as plt

        fig, ax = plt.subplots()
        grid_size = 5
        grid_x = np.tile(np.arange(grid_size), grid_size)
        grid_y = np.repeat(np.arange(grid_size), grid_size)
        pts = ax.scatter(grid_x, grid_y)

        selector = SelectFromCollection(ax, pts)

        print("Select points in the figure by enclosing them within a polygon.")
        print("Press the 'esc' key to start a new polygon.")
        print("Try holding the 'shift' key to move all of the vertices.")
        print("Try holding the 'ctrl' key to move a single vertex.")

        plt.show()

        selector.disconnect()

        # After figure is closed print the coordinates of the selected points
        print('\nSelected points:')
        print(selector.xys[selector.ind])

**Total running time of the script:** ( 0 minutes  0.209 seconds)



.. only :: html

 .. container:: sphx-glr-footer


  .. container:: sphx-glr-download

     :download:`Download Python source code: polygon_selector_demo.py <polygon_selector_demo.py>`



  .. container:: sphx-glr-download

     :download:`Download Jupyter notebook: polygon_selector_demo.ipynb <polygon_selector_demo.ipynb>`


.. only:: html

 .. rst-class:: sphx-glr-signature

    `Gallery generated by Sphinx-Gallery <https://sphinx-gallery.readthedocs.io>`_
