MATLAB: Finding intersection point between a scatter and vertical lines

intersectionscattervertical lines

Is there any way to find the y values of the intersection points between a scatter and vertical lines?

Best Answer

Use interp1. I had to do a fair amount of coding to get the data from your figure, but since you will have all the original data, you can skip directly to the YIsx = interp1 step:

openfig('figure 10.fig');               % Get figure & extract data
h1c = get(gca, 'Children');
Xdc = get(h1c, 'XData');
DSz = cellfun(@max,(cellfun(@size, Xdc, 'Uni',0))); % Get data sizes
IdxMx = find(DSz == max(DSz));
Xdmx = cell2mat(Xdc(IdxMx));
Xd = cell2mat(Xdc(setdiff(1:length(Xdc),IdxMx)));   % X-values of vertical lines
Ydc = get(h1c, 'YData');
Ydmx = cell2mat(Ydc(IdxMx));
% Yd = cell2mat(Ydc);
YIsx = interp1(Xdmx, Ydmx, Xd(:,1));    % Find intersections
hold on
plot(Xd(:,1), YIsx, '+r', 'MarkerSize',10, 'LineWidth',2)   % Plot intersections
hold off

produces:

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MATLAB: Finding intersection points with refline

It would be easier if you defined both of your functions in each plot with the same X-data. Then you could use the much more efficient code in How to change axis of graph and interpolate data.

This works for today’s plots (I tested it on all of them):

% GET INFORMATON FROM FIGURE: 
openfig('Figure(7).fig');
h1c = get(gca, 'Children');
Xdc = get(h1c, 'XData');
Ydc = get(h1c, 'YData');
maxlen = max(cell2mat(cellfun(@max, cellfun(@size, Xdc, 'Uni',0),'Uni',0)))
Xd2 = cell2mat(Xdc(2));
Yd2 = cell2mat(Ydc(2));
Xd = Xd2;
Yd1 = cell2mat(Ydc(1));
Yd = [Yd1(1)*ones(size(Xd2)); Yd2];
% CALCULATIONS: 
Ydn = diff(Yd, [], 1);              % Subtract line from curve to create zero-crossings
Zx = circshift(Ydn, [0 1]) .* Ydn;  % Use circshift to detect them
Zxi = find(Zx < 0);                 % Their indices
for k1 = 1:length(Zxi)              % Use interp1(Y,X,0) to get line intercepts as Xzx
    Xzx(k1) = interp1([Ydn(Zxi(k1)-1) Ydn(Zxi(k1))], [Xd(1,Zxi(k1)-1) Xd(1,Zxi(k1))], 0);
end
% PLOT ZERO-CROSSINGS ON FIGURE TO CHECK: 
hold on
plot(Xzx, repmat(Yd(1,1),1,length(Xzx)), '*r')
hold off

MATLAB: How to find intersection points between plot and straight line

That is my code, so I sort of remember what I was doing when I wrote it here nine months ago (in R2014a). What version of MATLAB are you using?

I’ll do my best to help, but I can’t figure out what you want to do. I don’t see a reference line in ‘Curve figure.fig’.

Best Answer

Related Solutions

MATLAB: Finding intersection points with refline

MATLAB: How to find intersection points between plot and straight line

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