How to use custom marker with plot?

Question

I would like to utilize customer markers in both scatter and line charts. How can I make custom marker out of a PNG file?

Answer 1

I don't believe matplotlib can customize markers like that. See here for the level of customization, which falls way short of what you need.

As an alternative, I've coded up this kludge which uses figimage to place images at the line point locations.

import matplotlib.pyplot as plt
import matplotlib.image as image

# constants
dpi = 72; imageSize = (32,32)
# read in our png file
im = image.imread('smile.png')

fig = plt.figure(dpi=dpi)
ax = fig.add_subplot(111)
# plot our line with transparent markers, and markersize the size of our image
line, = ax.plot((1,2,3,4),(1,2,3,4),"bo",mfc="None",mec="None",markersize=imageSize[0] * (dpi/ 96))
# we need to make the frame transparent so the image can be seen
# only in trunk can you put the image on top of the plot, see this link:
# http://www.mail-archive.com/[email protected]/msg14534.html
ax.get_frame().set_alpha(0)
ax.set_xlim((0,5))
ax.set_ylim((0,5))

# translate point positions to pixel positions
# figimage needs pixels not points
line._transform_path()
path, affine = line._transformed_path.get_transformed_points_and_affine()
path = affine.transform_path(path)
for pixelPoint in path.vertices:
    # place image at point, centering it
    fig.figimage(im,pixelPoint[0]-imageSize[0]/2,pixelPoint[1]-imageSize[1]/2,origin="upper")

plt.show()