How to draw polygon having set of unordered points?

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Abinaya 2014-3-17

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https://ww2.mathworks.cn/matlabcentral/answers/121856-how-to-draw-polygon-having-set-of-unordered-points

评论： Image Analyst 2018-11-14

How to draw polygon having set of unordered points in binary image.I want approximately all the points to be connected in the polygon which function would help?

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Answer 1

Image Analyst 2014-3-17

1
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https://ww2.mathworks.cn/matlabcentral/answers/121856-how-to-draw-polygon-having-set-of-unordered-points#answer_128745

在 MATLAB Online 中打开

There are multiple polygons that could be drawn this way. You must describe some algorithm for how to order them, such as the angle to the next point must always be clockwise (or counterclockwise) or something like that. You could find the centroid (average of x and y) then calculate angles of all points, and then sort based on angles. Is that what you want to do?

Here's some untested code:

meanx = mean(x);
meany = mean(y);
angles = atan( (y-ymean) ./ (x-xmean));
[sortedAngles, sortIndices] = sort(angles);
reorderedx = x(sortIndices);
reorderedy = y(sortIndices);
plot(reorderedx, reorderedy, 'bo-');

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Image Analyst 2014-3-17

编辑：Image Analyst 2017-6-10

在 MATLAB Online 中打开

Try this:

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 = 22;
x = rand(15,1);
y = rand(15,1);
subplot(1,2,1);
plot(x, y, 'rs-', 'LineWidth', 2);
grid on;
title('Random Points', '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') 
meanx = mean(x);
meany = mean(y);
angles = atan2( (y-meany),(x-meanx))
[sortedAngles, sortIndices] = sort(angles);
reorderedx = x(sortIndices);
reorderedy = y(sortIndices);
subplot(1,2,2);
plot(meanx, meany, 'g+', 'MarkerSize', 15);
hold on;
plot(reorderedx, reorderedy, 'bo-', 'LineWidth', 2);
grid on;
title('Sorted by Angle', 'FontSize', fontSize);

Wen Fang 2018-11-14

@Image Analyst

Image Analyst 2018-11-14

Try delaunayn()

T = delaunayn(X) computes a set of simplices such that no data points of X are contained in any circumspheres of the simplices. The set of simplices forms the Delaunay triangulation. X is an m-by-n array representing m points in n-dimensional space. T is a numt-by-(n+1) array where each row contains the indices into X of the vertices of the corresponding simplex.

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