Generate ColumnDataSource dictionary for segment labels.

def _get_seg_labels_data(self, order_seg, bins_seg):
        """Generate ColumnDataSource dictionary for segment labels.

        """

        if self.xticks is None:
            return dict(x=[], y=[], text=[], angle=[])

        mapping = self._compute_tick_mapping("angle", order_seg, bins_seg)

        values = [(text, ((end - start) / 2) + start)
                  for text, (start, end) in mapping.items()]

        labels, radiant = zip(*values)
        radiant = np.array(radiant)

        y_coord = np.sin(radiant) * self.max_radius + self.max_radius
        x_coord = np.cos(radiant) * self.max_radius + self.max_radius

        return dict(x=x_coord,
                    y=y_coord,
                    text=labels,
                    angle=1.5 * np.pi + radiant)