Warning
This page is located in archive. Go to the latest version of this course pages. Go the latest version of this page.

General Instructions for Creating Graphs and Figures

Examples below can be generated by plot_example.m or plot_example.py script in the Tools repository.

  • It's recommended to place your figures reasonably; prepare_figure function from the Tools can be used.
  • Do not forget to close your figures when not needed, e.g. close all figures at the beginning of your script.
matlab python
import matplotlib.pyplot as plt # assumed in every code bellow
close all plt.close( 'all' )
  • Each figure should a have descriptive title. Usually should be set after other drawing commands.
matlab python
title( 'My title' ) plt.title( 'My title' )
  • When necessary, a legend describing lines of different colors/styles should be added, preferably inside the plot, if possible.
matlab python
plot( …, 'DisplayName', 'Legend 1' ); plt.plot( …, label='Legend 1' )
hold on
plot( …, 'DisplayName', 'Legend 2' ); plt.plot( …, label='Legend 2' )
legend(); plt.legend()

Figures with Bitmap Image Superimposed

  • Show the image with axes.
  • Ensure square pixels.
matlab python
do not use imshow
image( rgb_img ) or imagesc( grayscale_img ) plt.imshow( img )
axis image [*] or axis equal plt.axis( 'image' ) [*] or plt.axis( 'equal' )

[*] This hides area outside the image.

Example image

2D Euclidean Plots

  • Ensure isotropic axis scale
  • Use labels for axes
  • Use text descriptions when needed
matlab python coment
plot( x, y, … ) plt.plot( x, y, … )
axis equal plt.axis( 'equal' ) scale
xlabel( 'x' ); plt.xlabel( 'x' ) labels
ylabel( 'y' ); plt.ylabel( 'y' )
text( x, y, '\alpha' ) plt.plot( x, y, 'a' ) text

Note that Matlab can plot greek numbers using TeX sequences ( '\\alpha', '\\beta', etc.).

3D Euclidean Plots

  • Same requirements as for 3D (scale, labels, …)
matlab python
from mpl_toolkits import mplot3d # 3D facilities, import before the .pyplot
ax = plt.axes( projection='3d' ) # 3D axis must be explicitly created
plot3( x, y, z, … ) ax.plot3D( x, y, z, … )
text( x, y, z, … ) ax.text3D( x, y, z, … )
axis( 'equal' ) plt.axis( 'equal' )
zlabel( 'z' ); ax.set_zlabel( 'z' )
Example 3D Plot

Plotting vectors

  • Bound vectors can be drawn using quiver… functions. Origin (X,Y,Z) and vector coordinates (dX,dY,dZ) must be given.
matlab python
quiver(X,Y,dX,dY,0) [*] plt.quiver(X,Y,dX,dY)
ax = plt.axes( projection='3d' )
quiver3(X,Y,Z,dX,dY,dZ,0) [*] ax.quiver3D(X,Y,Z,dX,dY,dZ)

[*] The scaling argument 0 ensures the arrow is of the proper length.

Example vector plot

Other Graphs

  • Use labels for axes. Don't forget units.
  • Set axis limits tightly to data, set axis to fit the figure.
matlab python
xlabel( 'time [s]' ) plt.xlabel( 'time [s]' )
ylabel( 'distance [m]' ) plt.ylabel( 'distance [m]' )
axis tight
plt.tight_layout()
Example graph.
courses/gvg/labs/hw-plotting.txt · Last modified: 2023/02/07 16:26 (external edit)