Matplotlib custom marker/symbol

Question

So there is this guide: http://matplotlib.org/examples/pylab_examples/scatter_symbol.html

# http://matplotlib.org/examples/pylab_examples/scatter_symbol.html
from matplotlib import pyplot as plt
import numpy as np
import matplotlib

x = np.arange(0.0, 50.0, 2.0)
y = x ** 1.3 + np.random.rand(*x.shape) * 30.0
s = np.random.rand(*x.shape) * 800 + 500

plt.scatter(x, y, s, c="g", alpha=0.5, marker=r'$\clubsuit$',
            label="Luck")
plt.xlabel("Leprechauns")
plt.ylabel("Gold")
plt.legend(loc=2)
plt.show()

But what if you are like me and don't want to use a clubsuit marker...

How do you make your own marker _________?

UPDATE

What I like about this special marker type is that it's easy to adjust with simple matplotlib syntax:

from matplotlib import pyplot as plt
import numpy as np
import matplotlib

x = np.arange(0.0, 50.0, 2.0)
y = x ** 1.3 + np.random.rand(*x.shape) * 30.0
s = np.random.rand(*x.shape) * 800 + 500

plt.plot(x, y, "ro", alpha=0.5, marker=r'$\clubsuit$', markersize=22)
plt.xlabel("Leprechauns")
plt.ylabel("Gold")
plt.show()

Countermeasure

have you had a look at this? – Spell

Yes I actually have. But it did not work out for me. What I like about the matplotlib example code are the 'c="g"' which I interpret as color adjustment for the plot (don't have a python shell in the writing moment to test it). – Countermeasure

Answer 1

The most flexible option for matplotlib is marker paths.

I used Inkscape to convert Smiley face svg into a single SVG path. Inkscape also has options to trace path in raster images. The I used svg path to convert it to matplotlib.path.Path using svgpath2mpl.

!pip install svgpath2mpl matplotlib
from svgpath2mpl import parse_path

import matplotlib.pyplot as plt      
import numpy as np                   
# Use Inkscape to edit SVG, 
# Path -> Combine to convert multiple paths into a single path
# Use Path -> Object to path to convert objects to SVG path
smiley = parse_path("""m 739.01202,391.98936 c 13,26 13,57 9,85 -6,27 -18,52 -35,68 -21,20 -50,23 -77,18 -15,-4 -28,-12 -39,-23 -18,-17 -30,-40 -36,-67 -4,-20 -4,-41 0,-60 l 6,-21 z m -302,-1 c 2,3 6,20 7,29 5,28 1,57 -11,83 -15,30 -41,52 -72,60 -29,7 -57,0 -82,-15 -26,-17 -45,-49 -50,-82 -2,-12 -2,-33 0,-45 1,-10 5,-26 8,-30 z M 487.15488,66.132209 c 121,21 194,115.000001 212,233.000001 l 0,8 25,1 1,18 -481,0 c -6,-13 -10,-27 -13,-41 -13,-94 38,-146 114,-193.000001 45,-23 93,-29 142,-26 z m -47,18 c -52,6 -98,28.000001 -138,62.000001 -28,25 -46,56 -51,87 -4,20 -1,57 5,70 l 423,1 c 2,-56 -39,-118 -74,-157 -31,-34 -72,-54.000001 -116,-63.000001 -11,-2 -38,-2 -49,0 z m 138,324.000001 c -5,6 -6,40 -2,58 3,16 4,16 10,10 14,-14 38,-14 52,0 15,18 12,41 -6,55 -3,3 -5,5 -5,6 1,4 22,8 34,7 42,-4 57.6,-40 66.2,-77 3,-17 1,-53 -4,-59 l -145.2,0 z m -331,-1 c -4,5 -5,34 -4,50 2,14 6,24 8,24 1,0 3,-2 6,-5 17,-17 47,-13 58,9 7,16 4,31 -8,43 -4,4 -7,8 -7,9 0,0 4,2 8,3 51,17 105,-20 115,-80 3,-15 0,-43 -3,-53 z m 61,-266 c 0,0 46,-40 105,-53.000001 66,-15 114,7 114,7 0,0 -14,76.000001 -93,95.000001 -76,18 -126,-49 -126,-49 z""")
smiley.vertices -= smiley.vertices.mean(axis=0)
x = np.linspace(-3, 3, 20)          
plt.plot(x, np.sin(x), marker=smiley, markersize=20, color='c')
plt.show()

Google Colab Link

Korwun

Nice! Any way to fill the marker with custom color? – Likker

Also, what does the smiley.vertices -= smiley.vertices.mean(axis=0) do? For some reason, my icon is shown up side down. Any idea why? – Likker

For reference, i found this tutorial that goes more into the detail of how to achieve this: petercbsmith.github.io/marker-tutorial.html – Twostep

Answer 2

So found out that it was just using mathtext symbols and not referring to any special vector based marker stored in the matplotlib module...

from matplotlib import pyplot as plt
import numpy as np
from numpy.random import randint
import matplotlib

x = np.arange(0.0, 100.0, 2.0)
y = x ** 1.3 + np.random.rand(*x.shape) * 30.0
s = np.random.rand(*x.shape) * 800 + 500

markers = ['\\alpha', '\\beta', '\gamma', '\sigma','\infty', \
            '\spadesuit', '\heartsuit', '\diamondsuit', '\clubsuit', \
            '\\bigodot', '\\bigotimes', '\\bigoplus', '\imath', '\\bowtie', \
            '\\bigtriangleup', '\\bigtriangledown', '\oslash' \
           '\ast', '\\times', '\circ', '\\bullet', '\star', '+', \
            '\Theta', '\Xi', '\Phi', \
            '\$', '\#', '\%', '\S']

def getRandomMarker():
    return "$"+markers[randint(0,len(markers),1)]+"$"

def getMarker(i):
    # Use modulus in order not to have the index exceeding the lenght of the list (markers)
    return "$"+markers[i % len(markers)]+"$"

for i, mi in enumerate(markers):
    plt.plot(x[i], y[i], "b", alpha=0.5, marker=getRandomMarker(), markersize=randint(16,26,1))
    plt.plot(x[i], y[i]+50, "m", alpha=0.5, marker=getMarker(i), markersize=randint(16,26,1))
    # Let's see if their "center" is located where we expect them to be...
    plt.plot(x[i], y[i]+100, "y", alpha=0.5, marker=getMarker(i), markersize=24)
    plt.plot(x[i], y[i]+100, "k+", markersize=12, markeredgewidth=2)

plt.xlabel("x-axis")
plt.ylabel("y-axis")
plt.xlim( -5, plt.xlim()[1]+5 )
plt.ylim( 0, plt.ylim()[1]*1.1 )
plt.gcf().set_size_inches(12,6)
plt.show()

Countermeasure

I was trying to find a 'filled heart' since \heartsuit is just an outline. Using a unicode marker worked for me: marker=ur'$\u2665$' – Lighterman

For those interested in removing the italics on normal letters/words, using the \mathrm or \rm mathtext command works. E.g. marker=r'$\mathrm{M}$' for an M. – Arthromere

List of all supported symbols: matplotlib.org/stable/tutorials/text/mathtext.html#symbols – Likker

you should use r-strings to avoid having to double-backslash latex commands, like e.g. markers = [r'\alpha', r'\beta', r'\gamma', ...] – Pitfall

Answer 3

Building on the answer from Vikas. Here's a script that generates a custom marker automatically from an SVG file.

"""
--------------------------------------------------
Script to generate custom marker from an SVG image
--------------------------------------------------

Heavily referenced from this tutorial: 
https://petercbsmith.github.io/marker-tutorial.html
"""

import matplotlib.pyplot as plt
import numpy as np

import matplotlib as mpl
from svgpathtools import svg2paths
from svgpath2mpl import parse_path

def generate_marker_from_svg(svg_path):
    image_path, attributes = svg2paths(svg_path)

    image_marker = parse_path(attributes[0]['d'])

    image_marker.vertices -= image_marker.vertices.mean(axis=0)

    image_marker = image_marker.transformed(mpl.transforms.Affine2D().rotate_deg(180))
    image_marker = image_marker.transformed(mpl.transforms.Affine2D().scale(-1,1))

    return image_marker

def demo_generation(svg_path):
    marker1 = generate_marker_from_svg(svg_path)

    x = np.linspace(0,2*np.pi,10)
    y = np.sin(x)

    plt.plot(x,y,'o',marker=marker1,markersize=30)

    plt.show()

if __name__ == "__main__":
    demo_generation("Icon-mode-bus-default.svg")

Forehead