How can I display the y-axis at each maximum point

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Muhammad Choudhury 2021-4-29

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https://ww2.mathworks.cn/matlabcentral/answers/817165-how-can-i-display-the-y-axis-at-each-maximum-point

评论： Muhammad Choudhury 2021-4-29

Is there a way in determining the y-axis values at each maximum point of this graph.

clear all;
% Importing video from files
vid = VideoReader('portfolio3/Tennis1.mp4');
% Converting the video into frames
frames = read(vid);
% Finding the size and length of the video
si = size(frames)
% % Creating a vector to store positions of the vector
posVec = [];
%% Cropping and greying the video for facile processing
% for all frames
for i = 1 : si(4)
    % Cropping frame by frame
    CroppedFrame = imcrop(frames(:,:,:,i),[120 90 450 1000]);
    
    % Coverting to grey 
    CroppedFrame = rgb2gray(CroppedFrame);
    
    % Binarising
    CroppedFrame = im2bw(CroppedFrame,0.7);
    
    % Removing flexes
    CroppedFrame = imopen(CroppedFrame,strel('disk',3));
    
    imshow(CroppedFrame);
    
    % Tracking the ball in the video
    
    [pos,rad] = imfindcircles(CroppedFrame,[13 100]);
    viscircles(pos,rad);
    drawnow
    
    % Adding the current position to the position vector
    posVec = [posVec; pos];
end
scatter(0-posVec(:,1),500-posVec(:,2));
pbaspect([1000 1000 1000])
hold on;
title('Bouncing Ball Trajectory')
xlabel('Horizontal Displacement')
ylabel('Vertical Displacement')

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Answer 1

DGM 2021-4-29

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https://ww2.mathworks.cn/matlabcentral/answers/817165-how-can-i-display-the-y-axis-at-each-maximum-point#answer_688185

编辑：DGM 2021-4-29

在 MATLAB Online 中打开

You can find the y-val and location of local maxima using findpeaks()

[peaks,loc,w] = findpeaks(mydata);

Just doing

findpeaks(mydata);

plots the series and places markers on the peaks that it found.

For example:

t = linspace(0,8.5*pi,100);
f = -t.^2.*sin(t) + t.^2;
[pk,loc]=findpeaks(f)
findpeaks(f)

gives

pk =
       0.1809        51.69       249.62       604.93       1118.3
loc =
     4    21    43    66    89

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DGM 2021-4-29

编辑：DGM 2021-4-29

在 MATLAB Online 中打开

You should just be running it on the y-data. Normally, you could run it on both x and y vectors, but your x-data isn't strictly increasing. Passing the y-data alone should be sufficient.

Consider this example using scattered data with non-monotonic x-data:

% plot points in a circle
r = 1;
th = linspace(0,2*pi,30);
x = r*cos(th);
y = r*sin(th);
scatter(x,y); axis equal
[pk,loc] = findpeaks(y) 
findpeaks(y)