intersection of lines and curves

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SHANTANU KSHIRSAGAR 2020-5-12

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https://ww2.mathworks.cn/matlabcentral/answers/524795-intersection-of-lines-and-curves

评论： Star Strider 2020-5-22

i have data in which line is plotted on a signal having pulses. I want to find out all points of intersections between the line and the curve. Right now i am able to get single point of intersection on only one side of pulse. I also need point of intersection on the other side.

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SHANTANU KSHIRSAGAR 2020-5-12

also in some cases getting wrong intersection, in remaining getting error of not having unique points(intersect1).

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Answer 1

Star Strider 2020-5-12

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https://ww2.mathworks.cn/matlabcentral/answers/524795-intersection-of-lines-and-curves#answer_432075

在 MATLAB Online 中打开

Try this:

D = load('intersect1.mat');
x_curve = D.x_curve;
y_curve = D.y_curve;
x_line  = D.x_line;
y_line  = D.y_line;
x_curve(x_curve == 0) = [];                                             % Eliminate Spurious Points
y_curve(y_curve == 0) = [];                                             % Eliminate Spurious Points
zci = @(v) find(v(:).*circshift(v(:), -1, 1) <= 0);                     % Returns Approximate Zero-Crossing Indices Of Argument Vector (>= R2016b)
icix = zci(y_curve - y_line(1:end-2));
figure
plot(x_curve, y_curve,    x_line, y_line)
hold on
plot(x_curve(icix), y_curve(icix), 'dr')
hold off
grid

producing:

The x-values of the intersections are about 0.135 and 0.149. (They are: x_curve(icix).)

The points are dense enough that it is not necessary to interpolate them to get reasonably precise values for the intersections.

.

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Star Strider 2020-5-13

在 MATLAB Online 中打开

Rather than write specific code for this, if you have the Signal Processing Toolbox, use the risetime function. (There are also related functions.) It is likely more robust than anything I can write.

Try this:

D = load('intersect3.mat');
x_curve = D.x_curve;
y_curve = D.y_curve;
% x_line = D.x_line;
% y_line = D.y_line;
stlvls = [0.75 3.1];
tolv = [min(y_curve) max(y_curve)];
pcrl = 100 * stlvls/diff(tolv);
[r,lt,ut,ll,ul] = risetime(y_curve, x_curve, 'PercentReferenceLevels',pcrl);
figure
plot(x_curve, y_curve)
hold on
plot([lt ut], [ll ul], 'dr')
hold off
grid

Here, the first output ‘r’ is the rise time between levels, the next two outputs are the times for both levels, and the last two are the levels themselves.

If you just want to get the intersections, my earlier code will do what you want. If you want transition times, state levels, and other parameters, the Signal Processing Toolbox functions are the best options.

(My spologies for the delay. I was locked out of my account for a while this morning. I still have no idea what that was about.)

Star Strider 2020-5-13

在 MATLAB Online 中打开

As always, my pleasure!

O.K. In that event, see if this does what you want.

Try this:

D = load('intersect3.mat');
x_curve = D.x_curve;
y_curve = D.y_curve;
x_line = D.x_line;
y_line = D.y_line;
stlvls = [0.75 3.1];
[ymin,mnix] = min(y_curve);
[ymax,mxix] = max(y_curve);
tlvl = interp1(y_curve(mnix:mxix), x_curve(mnix:mxix), stlvls, 'linear');
fprintf('risetime = %.6f\n', diff(tlvl))
figure
plot(x_curve, y_curve)
hold on
plot(tlvl, stlvls, 'dr')
hold off
grid

producing:

The rise time between the two levels is the difference between the ‘tlvl’ elements, and the times are those elements. This is subject to the constraints of interp1, that are explained in its documentation. The code works here, although it may not be robust for all waveforms.

For instances such as the earlier waveform, it would be necessary to sort the indices of the ‘icix’ vector for each intersecting line (assuming two different levels and four elements, so concatenate the elements in one vector, then sort), and then use interp1 if necessary to get the associated times. If the lines and curve have a large number of points, it may not be necessary to interpolate them to get accurate time estimates. Just use the indices, and do the appropriate arithmetic on the times derived from the indices to get the risetime and falltime.

SHANTANU KSHIRSAGAR 2020-5-22

编辑：SHANTANU KSHIRSAGAR 2020-5-22

Thank you star , I worked on your code for some time,made some changes, additions it is really helpful .

Star Strider 2020-5-22

As always, my pleasure!

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Answer 2

KALYAN ACHARJYA 2020-5-12

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https://ww2.mathworks.cn/matlabcentral/answers/524795-intersection-of-lines-and-curves#answer_431920

编辑：KALYAN ACHARJYA 2020-5-12

在 MATLAB Online 中打开

Have you tried this way?

data1
data2
diff=data1-data2;
small_value=??  % Define small value to deal with samll differenece also 
% Make the lower as possible, though ensure that it donot missed the interconnection
idx=find(diff<small_value);

If the data1 and data2 are non floating numbers, you can do the following

idx=find(data1==data2)

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Walter Roberson 2020-5-12

Do you mean that you are not permitted to use the functions there, or that you have technical problems when you try to use those functions?

If you are not permitted to use the functions there, then I would be concerned that if I were to give you code for this purpose, that you would not be permitted to use it.

SHANTANU KSHIRSAGAR 2020-5-12

编辑：SHANTANU KSHIRSAGAR 2020-5-12

thanks @Walter Roberson and @KALYAN ACHARJYA

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intersection of lines and curves

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intersection of lines and curves

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