Draw lines between points

I have a text file ("coordinates.txt") that contains x and y coordinates of points.

File looks like this:

11 44 2 9

11 44 5 8

2 1 6 11

2 1 10 3

I need to draw lines between (11, 44) to (2, 9), (11, 44) to (5, 8), (2, 1) to (6, 11), and (2, 1) to (10, 3).

I can do this by manually like:

x = [11 11 2 1; 2, 5, 6, 10]; 

y = [44 44 1 1; 9 8 11 3]; 

plot (x, y).

But the actual file is quite long and I need to "automate" this process.

I tried:

load coordinates.txt; 

edit coordinates.txt; 

x1= [coordinates(:, 1); coordinates(:, 3)]; 

y1 = [coordinates(:, 2); coordinates(:, 4)]; 

plot (x1, y1).

It gives me lines drawn from (11, 44) to (2, 9), (2, 9) to (5, 8), (5, 8) to (6, 11), (6, 11) to (10, 3).

Could anyone help?

Answer 1

[dpb]

Simply read in the array as it is in the file, then if

m =
  11    44     2     9
  11    44     5     8
   2     1     6    11
   2     1    10     3

for instance,

>> x=[m(:,1) m(:,3)];
>> y=[m(:,2) m(:,4)];
>> plot(x',y')

Or, you can do w/o the temporaries x, y of course if there's no other need to separate.

NB: I'm presuming the actual example x

x = [11 11 2 1; 2, 5, 6, 10];

contains a typo given the content of the file in that the '1' on the first line should also be a '2'...

[Emi]

It worked!! Thank you! And yes, it was a typo.

Answer 2

[Kelly Kearney]

Matlab considers each column passed to plot to represent a separate line segment. So just transpose your data:

plot(x1', y1')

Answer 3

[Bandar]

In this case you better build your own function to draw a line given two points.

function [] = drawLine(p1, p2)

theta = atan2( p2(2) - p1(2), p2(1) - p1(1));
r = sqrt( (p2(1) - p1(1))^2 + (p2(2) - p1(2))^2);

line = 0:0.01: r;
x = p1(1) + line*cos(theta);
y = p1(2) + line*sin(theta);

plot(x, y)

in the main function do the following

>> drawLine([0 0], [-5 5])
>> hold on 
>> drawLine([0 0], [5 5])

For many points just put `drawLine` in a loop. Hope this helps