MATLAB: How can i rotate an ellipse

ellipserotate

Im wondering how i can rotate an ellipse to a bearing/azimuth of 30deg about the xcenter and ycenter. Below is an example of how i have plotted the ellipse.

Thanks

xCenter = 50;

yCenter = 50;

xRad = 25;

yRad = 100;

theta = 0 : 0.01 : 2*pi;

x = xRad * cos(theta) + xCenter;

y = yRad * sin(theta) + yCenter;

plot(x, y, 'r');

axis([-50 150 -100 200]);

Best Answer

Hello,

Use this:

 clc;
xc=50; %xCenter
yc=50; %yCenter
a=25; %xRad
b=100; %yRad
m = 1000;
x = zeros(m,1);
y = zeros(m,1);
theta = linspace(0,2*pi,m);
for k = 1:m
        x(k) = a * cos(theta(k));
        y(k) = b * sin(theta(k));
end
alpha = input('Enter the rotation angle');
R  = [cos(alpha) -sin(alpha); ...
      sin(alpha)  cos(alpha)];
rCoords = R*[x' ; y'];   
xr = rCoords(1,:)';      
yr = rCoords(2,:)';      
plot(x+xc,y+yc,'r');
grid on;
hold on;
axis equal;
plot(xr+xc,yr+yc,'b');

Red ellipse is the original one and Blue is the rotated one.

Source: Answer 208806

Related Solutions

MATLAB: How to rotate

han han, I have not heard back from you so I assume you had trouble adapting my demos. So I did the thing 100% for you to give you exactly what you showed:

% Demo to rotate an ellipse about a center that also rotates around a circle.
% By ImageAnalyst
clc;    % Clear the command window.
clearvars;
close all;  % Close all figures (except those of imtool.)
imtool close all;  % Close all imtool figures.
clear;  % Erase all existing variables.
workspace;  % Make sure the workspace panel is showing.
fontSize = 14;
xCenter = 23.5;
yCenter = 0.5;
a = 2.0;
b = 0.5;
r = a;
% First get an ellipse centered at the origin of the proper size and shape.
hEllipse = imellipse(gca,[-a, -b, 2*a, 2*b]); % Second argument defines ellipse shape and position.
% Get (x,y) coordinates from the ellipse.
disp(hEllipse);
xy = hEllipse.getVertices();
% Clear original ellipse from axes.
axesHandlesToChildObjects = findobj(gca, 'Type', 'line');
if ~isempty(axesHandlesToChildObjects)
	delete(axesHandlesToChildObjects);
end
x = xy(:,1);
y = xy(:,2);
% plot(x, y, 'r-');
xy = [x y];
% Now rotate the ellipse through other angles and centers.
angles = 0 : 22.5 : 360 - 22.5;
for k = 1 : length(angles)
	theta = angles(k);
	rotationArray = [cosd(theta) sind(theta); -sind(theta) cosd(theta)];
	% Make a rotated ellipse about the origin.
	rotated_xy = xy * rotationArray;
	% Now shift its center.
	xCenter2 = xCenter + (r - 0.25) * cosd(theta);
	yCenter2 = yCenter + (r - 0.25) * sind(theta);
	x = rotated_xy(:,1) + xCenter2;
	y = rotated_xy(:,2) + yCenter2;
	% Now plot the rotated ellipse.
	plot(x, y, 'color', 'b', 'LineWidth', 2);
	if k == 1
		axis square;
		grid on;
		hold on;
	end
end
title('Demo Specially Made for han han', 'FontSize', 30);

If this does what you want, can you Accept this answer (since it seems no one else is going to offer a different working solution). Thanks in advance.

MATLAB: How to clear this plot

You should probably make your code into a function instead of copy-pasting it. That would highlight that you didn't define angles_Panel_0 or angles and used xy1 where you probably meant xy.

It would also show you that you forgot to do

delete(hEllipse1)

So the ellipse is still there.

You can use the code below, although you should add documentation for that function, and you should expain what you code is doing with comments.

angles_Panel_0=0;
xUECenter=5;
yUECenter=5;
a = 3;
b = 3;
r = a;
LineSpec='b';
plot_ellipse(a,b,r,xUECenter,yUECenter,angles_Panel_0,LineSpec)
angles=0;
xNodeCenter=6;
yNodeCenter=6;
a = 3;
b = 0.5;
r =  a;
LineSpec='m';
hold on;
plot_ellipse(a,b,r,xNodeCenter,yNodeCenter,angles,LineSpec)
hold off;
function plot_ellipse(a,b,r,xNodeCenter,yNodeCenter,angles,LineSpec)
%write documentation here explaing inputs and usage
hEllipse = imellipse(gca,[-a, -b, 2*a, 2*b]);  %#ok<IMELLPS>
xy = hEllipse.getVertices();
delete(hEllipse)
x = xy(:,1);
y = xy(:,2);
xy = [x y];
for k = 1 : length(angles)
    theta = angles(k);
    rotationArray = [cosd(theta) sind(theta); -sind(theta) cosd(theta)];
    rotated_xy = xy * rotationArray;
    xCenter = xNodeCenter + (r - 0.25) * cosd(theta);
    yCenter = yNodeCenter + (r - 0.25) * sind(theta);
    x = rotated_xy(:,1) + xCenter;
    y = rotated_xy(:,2) + yCenter;
    plot(x, y, LineSpec);
    if k == 1
        grid on;
        hold on;
    end
end
end

Best Answer

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MATLAB: How to rotate

MATLAB: How to clear this plot

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