MATLAB: Plotting random points within Boundary

Hello everyone,

I could use your help to improve the following code. Its about creating a map with random positions of points.

How to put points only inside of country borders?

 C = get(handles.number_cities, 'String');
        C = str2double(C);
        if(isnan(C)), errordlg('Parameters must be numerical.','Mapping Error');
        elseif(C <= 0), errordlg('Number of cities must be greater than zero','Mapping Error');
        else
            M = zeros(C,2);             % Map initialization
            for id_C = 1:1:C
                M(id_C,1) = randi(100); % Random map
                M(id_C,2) = randi(100);
            end

% Code to find the boundaries of a country on a map and place a specified number of points in it. clc; % Clear the command window. close all; % Close all figures (except those of imtool.) imtool close all; % Close all imtool figures if you have the Image Processing Toolbox. clear; % Erase all existing variables. Or clearvars if you want. workspace; % Make sure the workspace panel is showing. format long g; format compact; fontSize = 16; %=============================================================================== % Read in gray scale image. folder = pwd; baseFileName = 'map.jpg'; % 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 = 1. [rows, columns, numberOfColorBands] = size(rgbImage); % If it's RGB instead of grayscale, convert it to gray scale. if numberOfColorBands > 1 grayImage = rgbImage(:, :, 1); % Take red channel. else grayImage = rgbImage; end % Display the original image. subplot(2, 2, 1); imshow(rgbImage); axis on; impixelinfo; % Let user mouse around and see gray level. caption = sprintf('Original Image : %s', baseFileName); title(caption, 'FontSize', fontSize); impixelinfo; % Enlarge figure to full screen. g = gcf; g.WindowState = 'maximized'; g.NumberTitle = 'off'; g.Name = 'Demo by Image Analyst' drawnow; %=============================================================================== % Segment the image. % Display the histogram subplot(2, 2, 2); imhist(grayImage); grid on; title('Cropped Image Histogram', 'FontSize', fontSize); xlabel('Gray Level', 'FontSize', fontSize); ylabel('Pixel Count', 'FontSize', fontSize); % Specify a threshold. The image is 16 bits in the range 0-65535 so the threshold will be high. threshold = 240; % Place line on histogram at the mean. xline(threshold, 'Color', 'r', 'LineWidth', 2); % Create a binary image mask = grayImage > threshold; subplot(2, 2, 3); imshow(mask); title('Initial Mask', 'FontSize', fontSize); drawnow; % Get rid of any holes. mask = imfill(mask, 'holes'); % Take the largest region. mask = bwareafilt(mask, 1); subplot(2, 2, 3); imshow(mask); title('Final Mask', 'FontSize', fontSize); drawnow; %=============================================================================== % Get the perimeter. boundaries = bwboundaries(mask); boundaries = boundaries{1}; % Extract from cell. xb = boundaries(:, 2); yb = boundaries(:, 1); % Get random points. numPoints = nnz(grayImage); % Get way more points than we need. % Say how many points we need inside the boundary. numPointsNeeded = 300; xp = columns * rand(1, numPoints); yp = rows * rand(1, numPoints); % You can round them to integers if you want to or need to, like if you're going to use them as indexes in an array. subplot(2, 2, 4); imshow(rgbImage); drawnow; % Find out which points are in the polygon. numPointsInside = 0; insideBoundary = false(numel(xp), 1); for k = 1 : numel(xp) % Check if (xp, yp) is inside the boundaries defined by xb and yb. insideBoundary(k) = inpolygon(xp(k), yp(k), xb, yb); if insideBoundary(k) numPointsInside = numPointsInside + 1; if numPointsInside >= numPointsNeeded break; end end end % Plot them all x = xp(insideBoundary); y = yp(insideBoundary); hold on; plot(x, y, 'r.', 'MarkerSize', 10); caption = sprintf('Original image with %d locations', numPointsInside); title(caption, 'FontSize', fontSize); msgbox('Done! Thank you Image Analyst!');

Best Answer