MATLAB: How do you use inpolygon

coordinatesginputinpolygonuser input

I am trying to learn how to use this function. I have a photo of two buttons, and have acquired the bounding boxes for those buttons with their coordinates. The coordinates are saved in two matrices, one for x (Xcoordinates) and one for y (Ycoordinates).

Now I want the image to open and have the user click on one of the buttons using the inpolygon function. If the user clicks outside the bounding boxes, nothing is displayed, but if they click inside one of the buttons, information pertaining to that button is displayed.

I've defined xv to be Xcoordinates and yv to be Ycoordinates, for the inpolygon function, but I am not sure how the function works and how to implement for this thing I want to do.

Best Answer

Wouldn't it just be

xVertices = [Xcoordinates(1), Xcoordinates(2), Xcoordinates(2), Xcoordinates(1)];
yVertices = [Ycoordinates(1), Ycoordinates(1), Ycoordinates(2), Ycoordinates(2)];
itsInside = inpolygon(x, y, xVertices, yVertices);

where x and y are what you got from ginput(1)? But it sounds like you already tried that, so am I missing something? Do you need a full blown demo?

Related Solutions

MATLAB: How to extract the data using inpolygon function

Consult the inpolygon documentation page. You can probably do this without the for loop, as inpolygon can query a vector of points at once.

Here is an example from the linked page.

% Define polygon
L = linspace(0,2*pi,6);
xv = cos(L)';
yv = sin(L)';
% Define points to query
xq = randn(250,1);
yq = randn(250,1);
% Find points inside polygon
[in,on] = inpolygon(xq,yq,xv,yv);
% Visualize results
figure
plot(xv,yv) % polygon
axis equal
hold on
plot(xq(in),yq(in),'r+') % points inside
plot(xq(~in),yq(~in),'bo') % points outside
hold off

MATLAB: How to color a certain pixel value in only a region of interest (ROI) in an intensity image

See this demo:

clc;    % Clear the command window.
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.
format longg;
format compact;
fontSize = 20;
% Read in a standard MATLAB gray scale demo image.
folder = fullfile(matlabroot, '\toolbox\images\imdemos');
baseFileName = 'moon.tif';
% Get the full filename, with path prepended.
fullFileName = fullfile(folder, baseFileName);
% Check if file exists.
if ~exist(fullFileName, 'file')
  % File doesn't exist -- 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 in the search path folders.', 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.
subplot(2, 2, 1);
imshow(grayImage, []);
title('Original Grayscale Image', 'FontSize', fontSize);
% Enlarge figure to full screen.
set(gcf, 'units','normalized','outerposition',[0 0 1 1]);
% Give a name to the title bar.
set(gcf,'name','Demo by ImageAnalyst','numbertitle','off') 
uiwait(msgbox('Draw the ROI.  Left click to anchor vertices, then right click inside to finish it up.'));
binaryImage =roipolyold();
subplot(2, 2, 2);
imshow(binaryImage, []);
title('Your ROI', 'FontSize', fontSize);
% Find out where image is exactly 81 gray levels.
image81 = grayImage == 81;
% Mask by ROI to get only 81 pixels inside the ROI.
binaryImage = binaryImage & image81
subplot(2, 2, 3);
imshow(binaryImage, []);
title('Value = 81 AND inside Your ROI', 'FontSize', fontSize);
% Construct the RGB image
redChannel = grayImage;
greenChannel = grayImage;
blueChannel = grayImage;
redChannel(binaryImage) = 0;
greenChannel(binaryImage) = 255;
blueChannel(binaryImage) = 0;
% Display it.
rgbImage = cat(3, redChannel, greenChannel, blueChannel);
subplot(2, 2, 4);
imshow(rgbImage, []);
title('RGB image with green', 'FontSize', fontSize);

Best Answer

Related Solutions

MATLAB: How to extract the data using inpolygon function

MATLAB: How to color a certain pixel value in only a region of interest (ROI) in an intensity image

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