How to select a number of points from a 2D matlab plot?

I have created a matlab profile plot of an image and I would like to know if there is a way that would enable the user to select points from the 2D plot so that he can later on draw a best fit line on those points.

Thank you in advance

Answer 1

[Thorsten]

ginput does this job.

[UCL]

Thanks for that. Would you know how to now plot these points with a line of best fit across them? I want a straight line of best fit so as to find its equation as well. I know polyfit might work, but not how.

Thank you

[Thorsten]

If you ask a new question, please do so by starting a new question so others will have the chance to answer, too.

Answer 2

[Image Analyst]

UCL, try this demo:

% Make image that they can click on.
plot(cos(1:30),'b-');
grid on;
uiwait(msgbox('Click 5 points'));
[x y] = ginput(5)
hold on;
plot(x, y, 'r+', 'LineWidth', 2);
% Do the least squares fit
coeffs = polyfit(x, y, 1);
% Now find estimated values at 
% locations other than where they clicked.
xFitted = 1:30;  % x values that we want the fit for.
yFitted = polyval(coeffs, xFitted);
plot(xFitted, yFitted, 'r-', 'LineWidth', 2);

[UCL]

i tried this demo on my own profile plot but it only draws the line through the first 2-3 selected points and a bit more but then does not go through the other selected points which are on the opposite side of the plot.

[UCL]

i seem to have fixed it by increasing the xFitted=1:30 to 1:50 is that correct?

[Image Analyst]

It worked fine for me. It puts "+" markers where you click, and then it fits a line through the range 1-30 and draws a line with no markers through that range. You can fit over whatever range you want. I just picked 1 to 30 arbitrarily.

[UCL]

thank you very much !