CODEWITHSUNDEEP
matlabellipsedrawellipse
Dorian Kartalovski
Dorian Kartalovski

Reputation: 213

Draw Rotated Ellipses on Matlab

I am trying to plot a series of ellipses on Matlab. Basically I have a microscopic picture and I process it with ImageJ to obtain a series of data (area, center, major and minor axes) for each ellipse. I am trying to replot those ellipses on matlab in order to after add a gradient color to map the picture so I can tell from the ellipse in which direction the fibre is. This is my code 

clearvars -except data colheaders %Clear everything but the original data

data(:,9)=data(:,9)*pi/180; %Transform my 9th colomn (rotation angle) in rad
data(:,6)=1196-data(:,6); %Recalibrate the y axis (different coordinate system)

for i=1:29 %29 ellipses to plot
theta = 0 : 0.01 : 2*pi; 
x = data(i,7)/2 * cos(theta) * cos(data(i,9)) - data(i,8)/2 * sin(theta) * sin(data(i,9)) + data(i,5);
y = data(i,7)/2 * sin(theta) * cos(data(i,9)) + data(i,8)/2 * cos(theta) * sin(data(i,9)) + data(i,6);
plot(x, y, 'LineWidth', 1);
hold on
end 
% Columns (5,6) are the centre (x,y) of the ellipse
% Columns (7,8) are the major and minor axes (a,b)
% Column 9 is the rotation angle with the x axis

axis equal; % Keep axis same size as sample picture
xlim([0 1592]);
ylim([0 1196]);
grid on;

I can send a picture on private, seems they don't let me upload one. But i obtain circles at the right location instead of ellipses. Are my equations right ? Best Dorian

Upvotes: 1

Views: 1450

Answers (1)

Benoit_11
Benoit_11

Reputation: 13945

You're actually pretty close; you made a small mistake in the definition of the x value and simply need to swap data(i,8) with data(i,7).

i.e. change that line:

x = data(i,7)/2 * cos(theta) * cos(data(i,9)) - data(i,8)/2 * sin(theta) * sin(data(i,9)) + data(i,5);

for that one:

x = data(i,8)/2 * cos(theta) * cos(data(i,9)) - data(i,7)/2 * sin(theta) * sin(data(i,9)) + data(i,5);

Here is a test with dummy data:

clear
clc

%// Define dummy data
data = zeros(4,9);

data(:,5) = [1 ;2 ;3; 4];
data(:,6) = [1; 2 ;3; 4];
data(:,7) = [6 ;7;8;9];
data(:,8) = [2;3;4;5];

data(:,9) = [10;30;45;90];

data(:,9)=data(:,9)*pi/180;

%// You can put that outside the loop.
theta = 0 : 0.01 : 2*pi;

hold all
for i=1:size(data,1)

x = data(i,8)/2 * cos(theta) * cos(data(i,9)) - data(i,7)/2 * sin(theta) * sin(data(i,9)) + data(i,5);
y = data(i,7)/2 * sin(theta) * cos(data(i,9)) + data(i,8)/2 * cos(theta) * sin(data(i,9)) + data(i,6);


 plot(x, y, 'LineWidth', 1);

%// NEW to add text
text(data(i,5),data(i,6),['Ellipse' num2str(i)],'Color',rand(1,3))


end
axis equal;
grid on;

Output:

enter image description here

yay!

EDIT:

I added a line of code to label ellipses with text. I use random colors and place the text at the center of the ellipse but you can change it as you like to match the color with that of each ellipse.

Upvotes: 1

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