Draw and Color Overlapping Circles with Shapely in Python

Question

I am trying to draw and color overlapping circles using Shapely in Python. I’ve looked at several similar examples but keep running into problems with depreciated functions (like cascaded_union)

Here’s my code so far:

import matplotlib.pyplot as plt
from shapely.geometry import Point, Polygon, MultiPoint, MultiPolygon



def plot_coords(coords):
    pts = list(coords)
    x, y = zip(*pts)
    plt.plot(x,y)


def plot_polys(polys):
    for poly in polys:
        plot_coords(poly.exterior.coords)

points = [Point(0, 0),
             Point(2,0),
             Point(1,2),
             Point(-1,2),
             Point(-2,0),
             Point(-1,-2),
             Point(1,-2)]

for point in points:
    plot_polys([point.buffer(2.2)])
    
plt.show()

The output looks like so:

From here, I would like to fill in the circles with colors I choose. I want the overlapping areas to have mixed colors, but to do this I need to figure out how to define the overlap. I tried following along here with unary_union, but I am a bit lost how to do this on a series of buffered points.

Any help would be greatly appreciated! I’m also open to other methods of accomplishing this goal.

Asked By: Laura Morgan

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Source

Answer 1

maybe a step towards a solution, you can try the matplotlib.pyplot.fill_between methods for your circles and use the alpha argument to have different colors in overlying sections.

import matplotlib.pyplot as plt
from shapely.geometry import Point, Polygon, MultiPoint, MultiPolygon

def plot_coords(coords, col):
    pts = list(coords)
    x, y = zip(*pts)
    plt.plot(x, y, c=col)


def plot_polys(polys, col):
    for poly in polys:
        plot_coords(poly.exterior.coords, col=col)
        # the line I added
        plt.fill_between(*poly.exterior.xy, alpha=.5, color=col)


# define list of colors
colors = ['r', 'r', 'r', 'k', 'k', 'k', 'g', 'g']

# convert list to generator for easy iteration in loop
color_gen = (col for col in colors)


points = [Point(0, 0),
          Point(2, 0),
          Point(1, 2),
          Point(-1, 2),
          Point(-2, 0),
          Point(-1, -2),
          Point(1, -2)]

for point in points:
    plot_polys([point.buffer(2.2)], col=next(color_gen))

plt.show()

Answered By: AlexWach

Draw and Color Overlapping Circles with Shapely in Python

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