Generate ColumnDataSource dictionary for annular labels.

def _get_ann_labels_data(self, order_ann, bins_ann):
        """Generate ColumnDataSource dictionary for annular labels.

        """

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

        mapping = self._compute_tick_mapping("radius", order_ann, bins_ann)
        values = [(label, radius[0]) for label, radius in mapping.items()]

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

        y_coord = np.sin(np.deg2rad(self.yrotation)) * radius + self.max_radius
        x_coord = np.cos(np.deg2rad(self.yrotation)) * radius + self.max_radius

        return dict(x=x_coord,
                    y=y_coord,
                    text=labels,
                    angle=[0]*len(labels))