Python / Matplotlib：转换Axis <=>数据坐标系

Question

My question is quite simple : in matplotlib, how can I easily convert coordinates in Axis system to/from Data system (Ideally I'm looking for a simple function output_coords = magic_func(input_coords) )

Actually my exact problem is : I'd like to plot an matplotlib.patches.Ellipse with his center in Axis system but his size (width & length) in Data system. But the transforms.blended_transform_factory method doesn't work in this case.

Thanks !

Answer 1

To get transformations from the Axes instance ax , you can use

axis_to_data = ax.transAxes + ax.transData.inverted()
points_data = axis_to_data.transform(points_axis)
data_to_axis = axis_to_data.inverted()
numpy.testing.assert_allclose(points_axis, data_to_axis.transform(points_data))

Answer 2

No immediate solution found, need to write it by myself :

def axis_data_coords_sys_transform(axis_obj_in,xin,yin,inverse=False):
    """ inverse = False : Axis => Data
                = True  : Data => Axis
    """
    xlim = axis_obj_in.get_xlim()
    ylim = axis_obj_in.get_ylim()

    xdelta = xlim[1] - xlim[0]
    ydelta = ylim[1] - ylim[0]
    if not inverse:
        xout =  xlim[0] + xin * xdelta
        yout =  ylim[0] + yin * ydelta
    else:
        xdelta2 = xin - xlim[0]
        ydelta2 = yin - ylim[0]
        xout = xdelta2 / xdelta
        yout = ydelta2 / ydelta
    return xout,yout

Answer 3

在转换教程之后 ，最简单的方法是使用ax.transLimits 。

output_coords = ax.transLimits.transform(input_coords)