Finding Exact Intersection Points

Hello,

I am currently using R2016 Version of MATLAB. I was wondering if anybody would help me with following-

(i) Getting exact intersection points of a horizontal line drawn on a curve with the main curve

(ii) Manually drawing straight lines on Matlab figures [Ellipses shown on below figure] (like if we hold shift on Microsoft office, it lets you draw a straight line)

Answer 1

[Star Strider]

See Plot a point of intersection between 2 lines or curves for a typical approach to this problem. This will find all the intersections, however you will need to choose which ones.

The general approach would be (using created data):

x = 1:0.5:25;
y = (sin(5*pi*x/max(x))+randn(size(x))/10+1)*1E+10;
bluline = 1.49E+10;

zci = find(diff(sign(y - bluline)));

for k = 1:numel(zci)
    idxrng = max(1,zci(k)-1) : min(numel(x),zci(k)+1);
    x_int(k) = interp1(y(idxrng),x(idxrng),bluline);
    y_int(k) = interp1(x(idxrng),y(idxrng),x_int(k));
end

figure
plot(x, y, '-k', [min(x) max(x)],[1 1]*bluline,'-b')
hold on
plot(x_int, y_int, 'sr')
hold off
grid

Then choose the intersections you want to keep.