File:Transmission line animation3.gif
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Transmission_line_animation3.gif (300 × 60 pixels, file size: 138 KB, MIME type: image/gif, looped, 100 frames, 5.0 s)
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Summary
DescriptionTransmission line animation3.gif |
English: A wave traveling rightward along a lossless transmission line. Black dots represent electrons, and arrows show the electric field. |
Date | |
Source | Own work |
Author | Sbyrnes321 |
Licensing
I, the copyright holder of this work, hereby publish it under the following license:
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This file is made available under the Creative Commons CC0 1.0 Universal Public Domain Dedication. |
The person who associated a work with this deed has dedicated the work to the public domain by waiving all of their rights to the work worldwide under copyright law, including all related and neighboring rights, to the extent allowed by law. You can copy, modify, distribute and perform the work, even for commercial purposes, all without asking permission.
http://creativecommons.org/publicdomain/zero/1.0/deed.enCC0Creative Commons Zero, Public Domain Dedicationfalsefalse |
Source code
"""
(C) Steven Byrnes, 2014-2016. This code is released under the MIT license
http://opensource.org/licenses/MIT
This code runs in Python 2.7 or 3.3. It requires imagemagick to be installed;
that's how it assembles images into animated GIFs.
"""
from __future__ import division
import pygame as pg
from numpy import cos, pi, sin, linspace
import subprocess, os
directory_now = os.path.dirname(os.path.realpath(__file__))
frames_in_anim = 100
animation_loop_seconds = 5 #time in seconds for animation to loop one cycle
bgcolor = (255,255,255) #background is white
ecolor = (0,0,0) #electrons are black
wire_color = (200,200,200) # wire color is light gray
arrow_color = (140,0,0)
# pygame draws pixel-art, not smoothed. Therefore I am drawing it
# bigger, then smoothly shrinking it down
img_height = 180
img_width = 900
final_height = 60
final_width = 300
# ~23 megapixel limit for wikipedia animated gifs
assert final_height * final_width * frames_in_anim < 22e6
#transmission line thickness, and y-coordinate of the top of each wire
tl_thickness = 27
tl_top_y = 40
tl_bot_y = img_height - tl_top_y - tl_thickness + 2
wavelength = 1.1 * img_width
e_radius = 4
# dimensions of triangular arrow head (this is for the longest arrows; it's
# scaled down when the arrow is too small)
arrowhead_base = 9
arrowhead_height = 15
# width of the arrow line
arrow_width = 6
# number of electrons spread out over the transmission line (top plus bottom)
num_electrons = 100
# max_e_displacement is defined here as a multiple of the total electron path length
# (roughly twice the width of the image, because we're adding top + bottom)
max_e_displacement = 1/60
num_arrows = 20
max_arrow_halflength = 22
def tup_round(tup):
"""round each element of a tuple to nearest integer"""
return tuple(int(round(x)) for x in tup)
def draw_arrow(surf, x, tail_y, head_y):
"""
draw a vertical arrow. Coordinates do not need to be integers
"""
# calculate dimensions of the triangle; it's scaled down for short arrows
if abs(head_y - tail_y) >= 1.5 * arrowhead_height:
h = arrowhead_height
b = arrowhead_base
else:
h = abs(head_y - tail_y) / 1.5
b = arrowhead_base * h / arrowhead_height
if tail_y < head_y:
# downward arrow
triangle = [tup_round((x, head_y)),
tup_round((x - b, head_y - h)),
tup_round((x + b, head_y - h))]
triangle_middle_y = head_y - h/2
else:
# upward arrow
triangle = [tup_round((x, head_y)),
tup_round((x - b, head_y + h)),
tup_round((x + b, head_y + h))]
triangle_middle_y = head_y + h/2
pg.draw.line(surf, arrow_color, tup_round((x, tail_y)), tup_round((x, triangle_middle_y)), arrow_width)
pg.draw.polygon(surf, arrow_color, triangle, 0)
def e_path(param, phase_top_left):
"""
as param goes 0 to 1, this returns {'pos': (x, y), 'phase':phi},
where (x,y) is the coordinates of the corresponding point on the electron
dot path, and phi is the phase for an electron at that point on the path.
phase_top_left is phase of the left side of the top wire.
"""
# d is a vertical offset between the electrons and the wires
d = tl_thickness - e_radius - 2
# pad is how far to extend the transmission line beyond the image borders
# (since those electrons may enter the image a bit)
pad = 36
path_length = 2*(img_width + 2*pad)
howfar = param * path_length
# move right across top transmission line
if howfar <= path_length / 2:
x = howfar - pad
y = tl_top_y + d
phase = phase_top_left + 2 * pi * x / wavelength
return {'pos':(x,y), 'phase':phase}
# ...then move left across the bottom transmission line
x = path_length - howfar - pad
y = tl_bot_y + tl_thickness - d
phase = phase_top_left + 2 * pi * x / wavelength
return {'pos':(x,y), 'phase':phase}
def main():
#Make and save a drawing for each frame
filename_list = [os.path.join(directory_now, 'temp' + str(n) + '.png')
for n in range(frames_in_anim)]
for frame in range(frames_in_anim):
phase_top_left = -2 * pi * frame / frames_in_anim
#initialize surface
surf = pg.Surface((img_width,img_height))
surf.fill(bgcolor);
#draw transmission line
pg.draw.rect(surf, wire_color, [0, tl_top_y, img_width, tl_thickness])
pg.draw.rect(surf, wire_color, [0, tl_bot_y, img_width, tl_thickness])
#draw electrons. Remember, "param" is an abstract coordinate that goes
#from 0 to 1 as the electron position goes right across the top wire
#then left across the bottom wire
equilibrium_params = linspace(0, 1, num=num_electrons)
phases = [e_path(a, phase_top_left)['phase'] for a in equilibrium_params]
now_params = [equilibrium_params[i] + sin(phases[i]) * max_e_displacement
for i in range(num_electrons)]
coords = [e_path(a, phase_top_left)['pos'] for a in now_params]
for coord in coords:
pg.draw.circle(surf, ecolor, tup_round(coord), e_radius)
#draw arrows
arrow_params = linspace(0, 0.5, num=num_arrows)
for i in range(len(arrow_params)):
a = arrow_params[i]
arrow_x = e_path(a, phase_top_left)['pos'][0]
arrow_phase = e_path(a, phase_top_left)['phase']
head_y = img_height/2 + max_arrow_halflength * cos(arrow_phase)
tail_y = img_height/2 - max_arrow_halflength * cos(arrow_phase)
draw_arrow(surf, arrow_x, tail_y, head_y)
#shrink the surface to its final size, and save it
shrunk_surface = pg.transform.smoothscale(surf, (final_width, final_height))
pg.image.save(shrunk_surface, filename_list[frame])
seconds_per_frame = animation_loop_seconds / frames_in_anim
frame_delay = str(int(seconds_per_frame * 100))
# Use the "convert" command (part of ImageMagick) to build the animation
command_list = ['convert', '-delay', frame_delay, '-loop', '0'] + filename_list + ['anim.gif']
subprocess.call(command_list, cwd=directory_now)
# Earlier, we saved an image file for each frame of the animation. Now
# that the animation is assembled, we can (optionally) delete those files
if True:
for filename in filename_list:
os.remove(filename)
main()
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9 November 2014
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Date/Time | Thumbnail | Dimensions | User | Comment | |
---|---|---|---|---|---|
current | 01:53, 29 May 2016 | ![]() | 300 × 60 (138 KB) | Sbyrnes321 | don't change the arrow color, for image simplicity |
00:39, 10 November 2014 | ![]() | 300 × 60 (238 KB) | Sbyrnes321 | User created page with UploadWizard |
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