MATLAB: How to change imellipse to include theta

image processingimellipseimrect

Is there a way to hack imellipse such that I can draw an ellipse and then change the angle so that major and minor axes do not just lie on the x and y axes?

I'm currently "brute forcing" it but I was wondering if anyone knows of an easier way.

Best Answer

Anathea: Try this demo and see if it does what you want:

% Demo to rotate an ellipse over an image.
% By ImageAnalyst
clc;    % Clear the command window.
workspace;  % Make sure the workspace panel is showing.
fontSize = 14;
% Read in a standard MATLAB gray scale demo image.
folder = fullfile(matlabroot, '\toolbox\images\imdemos');
baseFileName = 'cameraman.tif';
fullFileName = fullfile(folder, baseFileName);
% Get the full filename, with path prepended.
fullFileName = fullfile(folder, baseFileName);
if ~exist(fullFileName, 'file')
  % Didn't find it there.  Check the search path for it.
  fullFileName = baseFileName; % No path this time.
  if ~exist(fullFileName, 'file')
    % Still didn't find it.  Alert user.
    errorMessage = sprintf('Error: %s does not exist.', fullFileName);
    uiwait(warndlg(errorMessage));
    return;
  end
end
grayImage = imread(fullFileName);
% Get the dimensions of the image.  numberOfColorBands should be = 1.
[rows columns numberOfColorBands] = size(grayImage);
% Display the original gray scale image.
imshow(grayImage, []);
title('Grayscale Image', 'FontSize', fontSize);
% Enlarge figure to full screen.
set(gcf, 'units','normalized','outerposition',[0 0 1 1]);
set(gcf,'name','Demo by ImageAnalyst','numbertitle','off') 
axis on;
hEllipse = imellipse(gca,[70 60 50 150]); % Second argument defines ellipse shape and position.
% Create a binary image ("mask") from the ROI object.
disp(hEllipse);
xy = hEllipse.getVertices()
% Clear lines from axes
axesHandlesToChildObjects = findobj(gca, 'Type', 'line');
if ~isempty(axesHandlesToChildObjects)
    delete(axesHandlesToChildObjects);
end
hold on;
x = xy(:,1);
y = xy(:,2);
xCenter = mean(x);
yCenter = mean(y);
plot(x, y);
x = x - xCenter;
y = y - yCenter;
xy = [x y]
for theta = 0:22.5:180
    rotationArray = [cosd(theta) sind(theta); -sind(theta) cosd(theta)];
    rotated_xy = xy * rotationArray;
    x = rotated_xy(:,1) + xCenter;
    y = rotated_xy(:,2) + yCenter;
    plot(x, y);
    promptMessage = sprintf('Rotated by %.1f degrees.\nDo you want to Continue processing,\nor Cancel to abort processing?', theta);
    button = questdlg(promptMessage, 'Continue', 'Continue', 'Cancel', 'Continue');
    if strcmp(button, 'Cancel')
        return;
    end
end

Related Solutions

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

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.

Best Answer

Related Solutions

MATLAB: How to clear this plot

MATLAB: How to rotate

Related Question