matplotlib-scalebar

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0.9.0 verified Mon Apr 27 auth: no python

Artist for matplotlib to display a scale bar. Current version: 0.9.0. Release cadence: infrequent, couple of years.

pip install matplotlib-scalebar

Common errors

error ImportError: cannot import name 'ScaleBar' from 'scalebar' ↓

cause Wrong import path. The package name is matplotlib_scalebar, not scalebar.

fix

Use: from matplotlib_scalebar.scalebar import ScaleBar

error AttributeError: 'ScaleBar' object has no attribute 'set_font_properties' ↓

cause You may be trying to set font properties on ScaleBar, which does not expose that directly. The text properties are internal.

fix

Modify the text via scalebar.text_props dict or by recreating the artist.

error TypeError: __init__() got an unexpected keyword argument 'location' ↓

cause The location parameter was renamed to 'loc' in version 0.8.0.

fix

Use loc='lower right' instead of location='lower right'.

Warnings

breaking ScaleBar no longer automatically rescales when axis limits change (fixed scale factor). Prior to 0.6.0 it auto-rescaled; now you must call scalebar.update() if you change limits after adding. ↓

fix Use scalebar.update() or recreate the ScaleBar after setting axis limits.

gotcha The unit string is not validated; if you pass an unknown unit like 'myunit', it will be displayed as-is. No error is raised. ↓

fix Use known units: 'm', 'cm', 'mm', 'um', 'nm', 'ft', 'in', etc.

gotcha ScaleBar uses the axes' x-axis data coordinates. If your data is not in physical units, the scale bar will be meaningless. Ensure you provide the correct calibration factor (dx) matching your data coordinates. ↓

fix Set dx to the length represented by one data unit in your desired physical unit.

Imports

ScaleBar

wrong

from scalebar import ScaleBar

correct

from matplotlib_scalebar.scalebar import ScaleBar

module is matplotlib_scalebar, not scalebar

Quickstart

Basic usage: create a ScaleBar with calibration factor (dx) and unit, then add to axes.

import matplotlib.pyplot as plt
from matplotlib_scalebar.scalebar import ScaleBar
import numpy as np

# Create sample data
x = np.linspace(0, 10, 100)
y = np.sin(x)

fig, ax = plt.subplots()
ax.plot(x, y)
ax.set_xlabel('Distance (μm)')

# Add a scale bar: dx=1 means one unit in data coordinates = 1 μm
scalebar = ScaleBar(1, 'um', length_fraction=0.25)
ax.add_artist(scalebar)
plt.show()