make_cylinder.py

#!/usr/bin/env python

from __future__ import division
import math
import optparse
import sys


#-------------------------------------------------------------------------------
# command line

parser = optparse.OptionParser(description='''
Creates a cylinder along the z-axis extending from -height/2 to height/2.
n_tall is optional; it will default to a value that creates square pixels.
You can also create circles by setting height to 0.
''')
parser.add_option('--radius', dest='radius', default=1,
                  action='store', type='float',
                  help='radius of cylinder (default 1)')
parser.add_option('--height', dest='height', default=1,
                  action='store', type='float',
                  help='height of cylinder (default 1)')
parser.add_option('--n_around', dest='n_around', default=32,
                  action='store', type='int',
                  help='number of pixels around the circumference (default 32)')
parser.add_option('--n_tall', dest='n_tall',
                  action='store', type='int',
                  help='number of pixels from top to bottom (optional)')
options, args = parser.parse_args()

# figure out how many pixels are needed around the cylinder
# in order to get square pixels
if not options.n_tall:
    circumference = options.radius * 2 * math.pi
    options.n_tall = int(options.n_around * options.height / circumference)

options.n_tall = max(1, options.n_tall)

#-------------------------------------------------------------------------------
# make cylinder

result = ['[']
z_min = -0.5*options.height
z_inc = options.height / max(options.n_tall - 1, 1)

for i in range(options.n_tall):
    z = z_min + i*z_inc

    for j in range(options.n_around):
        theta = j / options.n_around * math.pi * 2
        x = math.sin(theta) * options.radius
        y = math.cos(theta) * options.radius

        result.append('  {"point": [%.4f, %.4f, %.4f]},' % (x, y, z))

# trim off last comma
result[-1] = result[-1][:-1]

result.append(']')
print('\n'.join(result))

sys.stderr.write('\nn_around = %s\n' % options.n_around)
sys.stderr.write('n_tall = %s\n' % options.n_tall)
sys.stderr.write('total = %s\n\n' % (options.n_tall*options.n_around))