I would like to add a scalebar to a plot and use the following code:

import numpy as np
import matplotlib.pyplot as plt
from matplotlib.offsetbox import AnchoredOffsetbox

class AnchoredScaleBar(AnchoredOffsetbox):
    def __init__(self, transform, sizex=1, sizey=3, labelx='', labely='', loc=3,
             pad=0.1, borderpad=0.1, sep=1, prop=None, barcolor="black", barwidth=None, 
             **kwargs):
        """
        Draw a horizontal and/or vertical  bar with the size in data coordinate
        of the give axes. A label will be drawn underneath (center-aligned).
        - transform : the coordinate frame (typically axes.transData)
        - sizex,sizey : width of x,y bar, in data units. 0 to omit
        - labelx,labely : labels for x,y bars; None to omit
        - loc : position in containing axes
        - pad, borderpad : padding, in fraction of the legend font size (or prop)
        - sep : separation between labels and bars in points.
        - **kwargs : additional arguments passed to base class constructor
        """
        from matplotlib.patches import Rectangle
        from matplotlib.offsetbox import AuxTransformBox, VPacker, HPacker, TextArea, 
        DrawingArea
        bars = AuxTransformBox(transform)
        if sizex:
            bars.add_artist(Rectangle((0,0), sizex, 0, ec=barcolor, lw=barwidth, fc="none"))
        if sizey:
            bars.add_artist(Rectangle((0,0), 0, sizey, ec=barcolor, lw=barwidth, fc="none"))

        if sizex and labelx:
            self.xlabel = TextArea(labelx, minimumdescent=False)
            bars = VPacker(children=[bars, self.xlabel], align="center", pad=0, sep=sep)
        if sizey and labely:
            self.ylabel = TextArea(labely)
            bars = HPacker(children=[self.ylabel, bars], align="center", pad=0, sep=sep)

        AnchoredOffsetbox.__init__(self, loc, pad=pad, borderpad=borderpad,
                               child=bars, prop=prop, frameon=False, **kwargs)

        
def add_scalebar(ax, matchx=False, matchy=False, hidex=False, hidey=False, **kwargs):
    """ Add scalebars to axes
    Adds a set of scale bars to *ax*, matching the size to the ticks of the plot
    and optionally hiding the x and y axes
    - ax : the axis to attach ticks to
    - matchx,matchy : if True, set size of scale bars to spacing between ticks
                if False, size should be set using sizex and sizey params
    - hidex,hidey : if True, hide x-axis and y-axis of parent
    - **kwargs : additional arguments passed to AnchoredScaleBars
    Returns created scalebar object
    """
    def f(axis):
        l = axis.get_majorticklocs()
        return len(l)>1 and (l[1] - l[0])

    if matchx:
         kwargs['sizex'] = f(ax.xaxis)
         kwargs['labelx'] = str(kwargs['sizex'])
    if matchy:
         kwargs['sizey'] = f(ax.yaxis)
         kwargs['labely'] = str(kwargs['sizey'])
    
    sb = AnchoredScaleBar(ax.transData, **kwargs)
    ax.add_artist(sb)

    if hidex : ax.xaxis.set_visible(False)
    if hidey : ax.yaxis.set_visible(False)
    if hidex and hidey: ax.set_frame_on(False)

    return sb

Example data:

x = np.arange(10)
y = 3*x

#plot data
fig1, ax1 = plt.subplots()
ax1.set_xlabel('x')
ax1.set_ylabel('y')
ax1.plot(x,y)

Add scalebar with sizex=1, sizey=10:

AnchoredScaleBar(ax1.transData, sizex=1,sizey =10)

sb = add_scalebar(ax1, matchx=False, matchy = False)
ax1.add_artist(sb)

Plotted data scalebar

A scalebar is now added to the plot but instead of having a size of sizex=1, sizey=10 it adds a scalebar with the default size of sizex=1, sizey=3 as specified in the init function header.

However, the size of the scalebar changes when specifying sizex=1, sizey=10 in the init header.

????Is there a way to call AnchoredScaleBar and pass different sizex and sizey arguments without changing the values in the init header????

CodePudding user response：

You're not using the AnchoredScaleBar that you're initializing at the beginning of your snippet. You should rather do:

sb = add_scalebar(ax1, matchx=False, matchy=False, sizex=1, sizey=10)
ax1.add_artist(sb)

so that sizex and sizey are passed to AnchoredScaleBar through the kwargs