Draw a rhombus polygon.
            Horizontal size (-hor_size, +hor_size) and
            vertical size (-vert_size, +vert_size).
            with its center on position X,Y
            and with its str_id as text in the middle.

def rhombus_polygon(self, X, Y, str_id, hor_size, vert_size):
        """ Draw a rhombus polygon.
            Horizontal size (-hor_size, +hor_size) and
            vertical size (-vert_size, +vert_size).
            with its center on position X,Y
            and with its str_id as text in the middle.
        """
        x0, y0 = X - hor_size, Y   # mid_west
        x1, y1 = X, Y - vert_size  # mid_north
        x2, y2 = X + hor_size, Y   # mid_east
        x3, y3 = X, Y + vert_size  # mid_south

        polygon = SvgPolygon(4)
        polygon.set_stroke(width=2, color='black')
        poly_name = gui.SvgText(X, Y + 5, str_id)
        poly_name.attributes['text-anchor'] = 'middle'
        self.sheet.append([polygon, poly_name])

        mid_north = [x1, y1]
        mid_south = [x3, y3]
        mid_east = [x2, y2]
        mid_west = [x0, y0]
        
        polygon.add_coord(*mid_north)
        polygon.add_coord(*mid_east)
        polygon.add_coord(*mid_south)
        polygon.add_coord(*mid_west)

        return mid_north, mid_south, mid_east, mid_west