How can I convert the plot to NumPy? - matplotlib

Question

I want to save a plot (of a polygon that builds via code) to a NumPy (not as an image file), but I don't know how can do it?!
this is my code:
fig, ax = plt.subplots(figsize=(5.12, 5.12))
N = 3
val = np.random.rand(N, 2, 3)
patches = []
for i in range(3):
patches.append(Polygon(val[:, :, i], True))
p = PatchCollection(patches, alpha=0.6)
p.set_array(np.array([500,23,1002])) # assign values
ax.add_collection(p)
fig.colorbar(p)
plt.axis('off')
plt.show()
and plot of it:
a plot after run above code
can anyone tell me, how can I do it?

Answer 1

If you want to save the polygons, you only need to remember the vertices of each polygon. For each shape, and set of vertices, it may be better to save as a dictionary, because these are characteristics of the object which .json files are meant to handle.
From the docs, Polygon() has a method that retrieves the vertices for that polygon .get_xy() so we can use this to get a tuple of coordinates for each vertex.
The next thing you specified is to be able to save the values assigned within each triangle given by the array that is plugged into ax.add_collection. We can move this to the top of the code, and then iterate through the list of values, adding them as values in a dictionary of keys.
Then the code becomes:
import numpy as np
import matplotlib.pyplot as plt
from matplotlib.patches import Polygon
from matplotlib.collections import PatchCollection
import json # To save the dictionary format
fig, ax = plt.subplots(figsize=(5.12, 5.12))
N = 3
val = np.random.rand(N, 2, 3)
fill = [500,23,1002] # The fill values you want to save
patches = [] # The list to save each triangle object
keys = 'tri' # The names of each triangle
tri_dict = {} # Initialize the final dictionary
for i in range(3):
poly = Polygon(val[:, :, i], True)
vert = poly.get_xy() # Get the vertices for the Polygon
patches.append(poly)
my_dict = { # Create a dictionary of chartacteristics for a single triangle
'vertices':vert.tolist(),
'fill': fill[i]
}
tri_dict[keys+f'{i}'] = my_dict # For the tiangle name as the key,
# assign the corresponding values
# print(tri_dict) # To show that you are saving the information of each triangle within
# a dictionary of dictionaries
# Saving the dictionary as .json
jsonString = json.dumps(tri_dict, indent=4)
jsonFile = open(r"<YOUR PATH HERE>\\"+"data.json", "w")
jsonFile.write(jsonString)
jsonFile.close()
# Plot the resulting triangles
p = PatchCollection(patches, alpha=0.6)
p.set_array(fill)
ax.add_collection(p)
fig.colorbar(p)
plt.axis('off')
plt.show()
From here, you should be able to play with the structure to fit your use-case, but for the question asked, this should suffice. Hope this helps!