Drawing lines in matlab

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I have 3 simple questions:
1: I want draw a straight line. Ok i know its easy. I can use this command:
line([0 100],[50 50],'Marker','.','LineStyle','-','LineWidth',5, 'Color',[0 1 1])
But for this command i have to know "x - Start" and "x - End" point. I just want to give only the y value my command. Matlab should draw it automatically.
2: I want to draw a rectangular like in the picture but i have just one input point -> see picture... matlab should draw it automatically. Is this possible? If not, no problem
3: I want to capture the point. Is there a possibility to do that? My Input should the coordiante point (x/y) of this point and from this point i want to determine the direction ... above right/ left, below right/left.....
My Code:
clear all
clear clc
x1=[0 50 75 100]
y1=[100 75 50 25]
[xb,yb] = stairs(x1,y1);
axis([0 200 0 200])
xlim([0 150])
datacursormode on

Accepted Answer

Walter Roberson
Walter Roberson on 12 Dec 2016
You can use xlim() to find the current X right and left margin and pass those as the X values for line()

More Answers (3)

Jan on 12 Dec 2016
1. The corrdinates of the 1st point and 1 additional component of the 2nd point are not sufficient to define a line. You need either the slope in addition or the coordinates of both points. To draw the line "automatically", the line must be defined. Therefore question 1 cannot be solved.
2. Again: What does "automatically" mean? You only need the coordinates of the vertices, then line draws the line. But Matlab cannot guess magically, where the points should appear. So how are the wanted points stored?
3. What does "capture" exactly mean?
Image Analyst
Image Analyst on 2 Jan 2017
What about his question 1 and 2?
And you can capture a runaway dog, or you can capture the (x,y) location where a user clicked. But I don't understand your definition of capture. Do you mean that if the user, through some unknown or other means, adds a text string to your graph that you want to detect the fact that they added something?

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3mg4 on 12 Dec 2016
Make a line that starts way befor you need it eg from -100 to +100, then give matlab the y value and let it plot.
Use teh axis command to restricct the visible area

Arash Ebrahimi
Arash Ebrahimi on 7 Jul 2017
hello how can I draw a line in matlab with slope and a point ?
  1 Comment
Walter Roberson
Walter Roberson on 7 Jul 2017
If you have the stats toolbox you can use refline()
Otherwise, use the old
y = m * x + b
where m is the slope = tan(theta) if you use angles, and b is the intercept.
If you need to solve for the intercept given a point, that is simple:
b = known_y - m * known_x

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