def relbezier(self, x1, y1, x2, y2, x, y):
        self.path.append('c' + str(x1) + ',' + str(y1) + ' ' +
                         str(x2) + ',' + str(y2) + ' ' + str(x) + ',' + str(y))
bezier with xy1 and xy2 to xy relative
dataset/ETHPy150Open CGATOxford/cgat/CGAT/SVGdraw.py/pathdata.relbezier