VectorFieldPlot

A python module for creating SVG images of electric and magnetic field lines for user defined charge and current configurations.

This module is an adaptation of the code written by Geek3 to create high quality, physically correct images of electric and magnetic field lines.

http://commons.wikimedia.org/wiki/User:Geek3/VectorFieldPlot

The version posted by Geek3 was a single python script that generated the field lines. It contained a set of classes and utility functions for creating the lines, and then a short program at the end that used these classes to create an image for a specific charge configuration. The images created by the script are fantastic, it does a great job.

This project just organized the classes that do the work into their own module so that it can be used by multiple programs at once. This initial commit is a straight copy of version 1.3 posted by Geek3.

Installing

$ pip install vectorfieldplot

Using

The vectorfieldplot module provides classes to build and render images. To create an image we create a document. We add a field to the document and then add elements to the field (sources of the field). After that, we add lines to the document, these are the field lines that will actually be drawn on the image. This is usually the most difficult part and will require some trial and error to get right. After lines are added we write the document which will create an SVG image.

Here is an example program that uses the module to generate a picture of the field lines for an electric dipole consisting of a positive and negative charge on the x-axis.

#!  /usr/bin/env python

'''An example script that generates a picture of the field lines for an electric dipole.'''

import math
import vectorfieldplot as vfp


# create a document. we specify the file name and image size here
doc = vfp.FieldplotDocument( 'ElectricDipole', width=800,height=600,unit=100)

# create a field opbject
field = vfp.Field()
# add the point charges
field.add_element('monopoles' , [ [ 1,0, 1]  # the positive charge
                                , [-1,0,-1]  # the negative charge
                                ] )

# draw the charges for the field on the document
doc.draw_charges(field)

# start drawing the field lines
# we are going to draw 20 field lines coming off of the positive charge at uniformly spaced angles.
N = 20
for i in range(N):
    # compute the angle that the line will start off at
    angle = i * 2.*math.pi / (N-1)
    # generate the line
    # this takes the initial position, the x and y components of the initial direction, and whether or not should go forward
    # or backward.
    line = vfp.FieldLine( field, [1,0], start_v=[math.cos( angle ) , math.sin( angle )],directions='forward' )
    # draw the line on the document
    doc.draw_line(line,arrows_style={'min_arrows':1,'max_arrows':1})

# write the document
doc.write()

Running this script will create an image named ElectricDipole.svg that looks like this:

This example will draw the field for a dipole directly using the dipole element:

#!  /usr/bin/env python

'''An example script that generates a picture of the field lines for an electric dipole.'''

import math
import vectorfieldplot as vfp


# create a document. we specify the file name and image size here
doc = vfp.FieldplotDocument( 'ElectricDipole2', width=800,height=600,unit=100)

# create a field opbject
field = vfp.Field()
# add the dipole
# note, parameters should be [ r_x, r_y, p_x, p_y ], where r is the position vector and p is the dipole moment.
field.add_element('dipoles' , [ [ 0,0,1,0] ] )

# draw the charges for the field on the document
doc.draw_charges(field)

# start drawing the field lines
# we are going to draw 100 field lines coming off of the positive charge at uniformly spaced angles.
N = 100
for i in range(N):
    # compute the angle that the line will start off at
    angle =  -math.pi/2 + i * math.pi / (N-1)
    # generate the line
    # this takes the initial position, the x and y components of the initial direction, and whether or not should go forward
    # or backward.
    line = vfp.FieldLine( field, [0.1*math.cos(angle),0.1*math.sin(angle)], start_v=[math.cos( angle ) , math.sin( angle )],directions='forward' )
    # draw the line on the document
    doc.draw_line(line,arrows_style={'min_arrows':1,'max_arrows':1})

# write the document
doc.write()

Messages and logging

By default, the software only prints out messages that are significant warnings or errors. To change this default, you can do the following:

import logging
logging.basicConfig(level=logging.DEBUG) # can be DEBUG, INFO, WARNING, or ERROR