How to draw a line through a set of points?

Hi, I have an image and a set of points present in the image. These points are not aligned with each other and I would like to draw a line that intersects the points

[Ameer Hamza]

Do you have the coordinates of these points?

[Rik]

question continued here

@Valerio: please don't open a new equivalent question.

[John D'Errico]

PLEASE DON'T ASK THE SAME QUESTION REPEATEDLY!

I've deleted my answer. since you already have answers to your last question.

Answer 1

[Image Analyst]

You forgot to attach your points, which would have been helpful.

Since your definition of "through" is a regression rather than to have the line connect all the points, use polyfit()

coefficients = polyfit(x, y, 1);
%xFit = x; % Option 1 : same number of points as the training set.
xFit = linspace(min(x), max(x), 2000); % Option 2 : lots of points, and not just where the training points are.
yFit = polyval(coefficients, xFit);
plot(x, y, 'r+', 'LineWidth', 2, 'Markersize', 15)
hold on;
plot(xFit, yFit, 'm-', 'LineWidth', 2)

[valerio auricchio]

I have some points in an immage, the point have x,y coordinate.

If i have 70 point what option i have to do?

[Image Analyst]

The code should work with x and y each having 70 points, though I didn't test it. Did you try it? If it doesn't work, attach your data (x and y points in a .mat file). If you want the points to be plotted over an image instead of just a graph, then attach your image also.

How many output locations do you want your regression fit to be evaluated at? At the same 70 x values as the training set? At more? If so, how many more?

[valerio auricchio]

I have an immage, i have indivituated some points in the immage where the intensity is more than 210.

The immage that i have is this:

Now i want to do a regression with this point to obtain a line. I used yout method and it worked but I'm asking if this is the corret things to do.

[Image Analyst]

The code will fit a line through those. If that's what you want to do, then it's the correct thing to do. Why do you have doubts? Why do you want a line anyway?

[valerio auricchio]

Ok niìow i dont have any dubts! I want a line becouse i have to intersecate this line with an other and obtain the angle

[Image Analyst]

Please attach your original image without the cyan markers on it, so I can get the points via thresholding:

mask = grayImage >= 200;
[y, x] = find(mask);
hold on
plot(x, y, 'c.');
hold off;

or else, supply me with a list of the x,y points you want to use.

And tell me the definition of the other line so I can find the angles of both of them and the acute angle between them.

[valerio auricchio]

No it's all right i find what i nedd thanks a lott!!1

Answer 2

[Ameer Hamza]

If you have the coordinates then you can use plot()

img; % your image
x; % x-coordinates of points
y; % y-coordinates of points

imshow(img);
hold on
plot(x, y)

[valerio auricchio]

And if i have more than one point, for example the coordinate of a set of point.

A=[x,x,x,x,x,x,x]

B=[y,y,y,y,y,y,y]

what i have to do?

[Ameer Hamza]

The answer assumes that x and y are vectors with several points. You can try

plot(A, B)

[valerio auricchio]

With plot(A,B) i'm nott plottinng a line but only the point. I want to plot the line

[Ameer Hamza]

This is strange behaviour. Normallt

plot(A, B)

should draw a line. But If you do something like this

plot(A, B, '+')

then only markers are shown.

Can you show your code?

[Aniket Agrawal]

how can i store that curve produced using plot(x,y) in a variable.

[Rik]

You can store a handle to the graphics object. Is that what you mean by storing the curve?