Simple code to draw a 2-D ellipse

Sometime you want to add ellipses to your figures or images in Matlab? Rather than update to Matlab 2010 or buy PDE toolbox, you could google around and hopefully you find here: A simple code illustrates how you can do it.

Content

• Input parameters of 2-D ellipse
• draw 'ellip = scaled circle' at origin
• Rotate to derised angle
• Move to derised location

Input parameters of 2-D ellipse

clc, clear, close all 
x0 = 3; y0 = 3; % Center of ellip 
a = 2; b = 1;   % Major and minor radius 
phi = 30;       % Orientation (degree) 
num = 100;      % #points -> smoothness 

draw 'ellip = scaled circle' at origin

theta = linspace(0,2*pi,num);
p(1,:) = a*cos(theta);
p(2,:) = b*sin(theta);
figure(1), hold on 
plot(p(1,:),p(2,:),'k--','LineWidth',2)
axis equal

Rotate to derised angle

phi = phi*pi/180; % deg->rad 
% Rotation matrix: 
Q = [cos(phi) -sin(phi)
    sin(phi)  cos(phi)];
p = Q*p;
plot(p(1,:),p(2,:),'g--','LineWidth',2)
plot(0,0,'r+')

Move to derised location

p(1,:) = p(1,:) + x0;
p(2,:) = p(2,:) + x0;
plot(p(1,:),p(2,:),'LineWidth',2)
plot(x0,y0,'r+')

Next post will present some examples of "real application" visualization with the help of ellipses.
Any thoughts or comments will be appreciate!