Replaced the node / edge dicts with custom data types.

        return self._xy_extent

    @property

    def pixel_area(self):

        if not getattr(self, '_pixel_area', None):

            extent = self.xy_extent

            self._pixel_area = extent[1][0] * extent[1][1]

        return self._pixel_area

    @property

    def pixel_width(self):

        if not getattr(self, '_pixel_width', None):

from scipy.spatial import ConvexHull

def convex_hull_ratio(points, ideal_area):

    """

    Parameters

    ----------

    points : ndarray

             (n, 2) array of point coordinates

    ideal_area : float

                 The total area that could be covered

    Returns

    -------

    ratio : float

            The ratio convex hull volume / ideal_area

    """

    hull = ConvexHull(points)

    return hull.volume / ideal_area

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