MATLAB: How to find all points inside a ellipse

MATLAB

I have the bounds of an ellipse in x- and y-coordinates. My end goal is to get a matrix of all x-values and a corresponding matrix of all y-values for the points in/out that ellipse. If possible, I would also like to color in the specified ellipse on a 2d plot. Does anyone know which commands/functions I can use to do this? Most of what I have seen simply confirms whether input values lie in/out an ellipse. Thank you!

such that a sample of the ellipse is represented as :

 xCenter = 15;
yCenter = 10;
xRadius = 1.5;
yRadius = 80;
theta = 0 : 0.01 : 2*pi;
x = xRadius * cos(theta) + xCenter;
y = yRadius * sin(theta) + yCenter;
plot(x, y, 'LineWidth', 3);

Best Answer

‘My end goal is to get a matrix of all x-values and a corresponding matrix of all y-values for the points in/out that ellipse.’

There would be an infinite number of them, since you have defined an infinite 2D space. Your computer (or any computer) likely cannot handle it.

‘If possible, I would also like to color in the specified ellipse on a 2d plot’

That’s more tractable. See the patch (link) and related functions (such as area and fill, linked to at the end of that page) to create your plot. Remember to specify axis equal to avoid distorting your ellipse plot.

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MATLAB: To plot an ellipse

See the FAQ: http://matlab.wikia.com/wiki/FAQ#How_do_I_create_an_ellipse.3F

MATLAB: Coordinate edge of the ceramic into pixel (x,y)

This would be more accurate if you used a black velvet fabric behind your tile. Then you'd simply threshold and call bwboundaries() or bwperim(). You can still try it with a gray background like you have but your edge may not be as sharp and linear. But try this demo code on your image:

clc;
clearvars;
close all;
workspace;
fontSize = 20;
% Read in a tile color demo image.
folder = 'C:\Users\Kurniawan\Documents';
baseFileName = 'tile.jpg';
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
rgbImage = imread(fullFileName);
% Get the dimensions of the image.  numberOfColorBands should be = 3.
[rows columns numberOfColorBands] = size(rgbImage);
% Display the original color image.
subplot(2, 2, 1);
imshow(rgbImage, []);
title('Original Color Image', 'FontSize', fontSize);
% Enlarge figure to full screen.
set(gcf, 'units','normalized','outerposition',[0 0 1 1]);
% Extract the individual red, green, and blue color channels.
% redChannel = rgbImage(:, :, 1);
% greenChannel = rgbImage(:, :, 2);
blueChannel = rgbImage(:, :, 3);
subplot(2, 2, 2);
imshow(blueChannel, []);
title('Blue Channel Image', 'FontSize', fontSize);
% Threshold blue channel
binaryImage = blueChannel < 163;
% Get rid of small blobs.
binaryImage = bwareaopen(binaryImage, 10000);
% Fill in any holes in the tile.
binaryImage = imfill(binaryImage, 'holes');
% Display it.
subplot(2, 2, 3);
imshow(binaryImage, []);
title('Binary Image', 'FontSize', fontSize);
% Get the boundary coordinates
tileBoundary = bwboundaries(binaryImage);
% Plot boundaries over original image.
subplot(2, 2, 4);
imshow(rgbImage, []);
title('Original Color Image with Boundary', 'FontSize', fontSize);
hold on;
thisBoundary = tileBoundary{1};
xCoordinates = thisBoundary(:, 2);
yCoordinates = thisBoundary(:, 1);
plot(xCoordinates, yCoordinates, 'b-', 'LineWidth', 3);

Best Answer

Related Solutions

MATLAB: To plot an ellipse

MATLAB: Coordinate edge of the ceramic into pixel (x,y)

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