draw_circle_surrounded_by_circles.py

   1 #!/usr/bin/env python3
   2 #
   3 # Draw a circle surrounded by other circles
   4 #
   5 # Copyright (C) 2018  Antonio Ospite <ao2@ao2.it>
   6 # SPDX-License-Identifier: WTFPL
   7 #
   8 # Using a formula from:
   9 # https://math.stackexchange.com/questions/12166/numbers-of-circles-around-a-circle
  10
  11 from math import pi, sin, cos, degrees
  12 import svgwrite
  13
  14
  15 def calc_inner_circle_radius(outer_circles_radius, number_of_circles):
  16     if outer_circles_radius <= 0:
  17         raise ValueError("Radius of outer circles cannot be zero")
  18
  19     if number_of_circles < 3:
  20         raise ValueError("Number of outer circles cannot be smaller than 3")
  21
  22     # Ratio between the inner circle and the outer circles
  23     ratio = sin(pi / number_of_circles) / (1 - sin(pi / number_of_circles))
  24
  25     inner_circle_radius = outer_circles_radius / ratio
  26
  27     return inner_circle_radius
  28
  29
  30 def write_svg(filename, inner_circle_radius, outer_circles_radius,
  31               number_of_circles, unit=""):
  32     border = 10
  33
  34     width = height = (inner_circle_radius + outer_circles_radius + border) * 2
  35
  36     svg = svgwrite.Drawing(filename, profile='full',
  37                            size=(str(width) + unit, str(height) + unit),
  38                            viewBox=('0 0 %g %g') % (width, height))
  39
  40     cx_inner = cy_inner = width / 2
  41
  42     inner_circle = svgwrite.shapes.Circle(center=(cx_inner, cy_inner),
  43                                           r=inner_circle_radius,
  44                                           fill='none',
  45                                           stroke='black',
  46                                           stroke_width=0.5)
  47     svg.add(inner_circle)
  48
  49     # Add a group for the first outer circle for extra flexibility.
  50     outer_circle_group = svgwrite.container.Group()
  51     svg.add(outer_circle_group)
  52
  53     cx_outer = cx_inner + sin(0) * (inner_circle_radius +
  54                                     outer_circles_radius)
  55     cy_outer = cy_inner + cos(0) * (inner_circle_radius +
  56                                     outer_circles_radius)
  57     outer_circle = svgwrite.shapes.Circle(center=(cx_outer, cy_outer),
  58                                           r=outer_circles_radius,
  59                                           fill='none',
  60                                           stroke='black',
  61                                           stroke_width=0.5)
  62     outer_circle_group.add(outer_circle)
  63
  64     # Clone the group for the other outer circles to make it easier to keep
  65     # visual symmetry by editing just the first group added above.
  66     for i in range(1, number_of_circles):
  67         theta = i * 2 * pi / number_of_circles
  68         outer_circle_clone = svgwrite.container.Use(outer_circle_group,
  69                                                     insert=(0, 0),
  70                                                     transform="rotate(%f, %f, %f)" %
  71                                                     (degrees(theta),
  72                                                      cx_inner,
  73                                                      cy_inner))
  74         svg.add(outer_circle_clone)
  75
  76     svg.save()
  77
  78
  79 def main():
  80     outer_circles_radius = 2.5
  81     number_of_circles = 22
  82
  83     inner_circle_radius = calc_inner_circle_radius(outer_circles_radius, number_of_circles)
  84
  85     write_svg("circle-surrounded-by-circles.svg", inner_circle_radius,
  86               outer_circles_radius, number_of_circles, unit="mm")
  87
  88
  89 if __name__ == "__main__":
  90     main()