Combine multiple matplotlib axes without re-plotting data-CodePudding

optional context feel free to skip: I'm currently using cartopy and matplotlib to read in and plot weather model data on a map. I have three different fields I'm plotting: temperature, wind, and surface pressure. I'm using contourf, barbs, and contour respectively to plot each field. I want one image for each field, and then I'd like one image that contains all three fields overlaid on a single map. Currently I'm doing this by plotting each field individually, saving each of the individual images, then replotting all three fields on a single ax and a new fig, and saving that fig. Since the data takes a while to plot, I would like to be able to plot each of the single fields, then combine the axes into one final image.

I'd like to be able to combine multiple matplotlib axes without replotting the data on the axes. I'm not sure if this is possible, but doing so would be a pretty major time and performance saver. An example of what I'm talking about:

from matplotlib import pyplot as plt
import numpy as np
x1 = np.linspace(0, 2*np.pi, 100)
x2 = x1   5
y = np.sin(x1)

firstFig = plt.figure()
firstAx = firstFig.gca()
firstAx.scatter(x1, y, 1, "red")
firstAx.set_xlim([0, 12])
secondFig = plt.figure()
secondAx = secondFig.gca()
secondAx.scatter(x2, y, 1, "blue")
secondAx.set_xlim([0, 12])

firstFig.savefig("1.png")
secondFig.savefig("2.png")

This generates two images, 1.png and 2.png.

Is it possible to save a third file, 3.png that would look something like the following, but without calling scatter again, because for my dataset, the actual plotting takes a long time?

CodePudding user response：

If you just want to save images of your plots and you don't intend to further use the Figure objects, you can use the following after saving "2.png".

# get the scatter object from the first figure
scatter = firstAx.get_children()[0]
# remove it from this collection so you can assign it to a new axis
# the axis reassignment will raise an error if it already belongs to another axis
scatter.remove()
scatter.axes = secondAx
# now you can add it to your new axis
secondAx.add_artist(scatter)
secondFig.savefig("3.png")

This modifies both figures, as it removes a scatter from one and adds it to another. If for some reason you want to preserve them, you can copy the contents of secondFig to a new one and then add the scatter to that. However, this will still modify the first plot as you have to remove the scatter from there.