why cant i rotate the 2nd line at the X axis it takes reference as point 0,0 and rotates at 45 degree angle i want to rotate the line at same axis

[Walter Roberson]

How are you creating the lines?

[Prakash Choudhary]

close all;
clc;
clear all;
x0=  [0 0];
y0=  [-85 85];
x1 = [820 820 ];
y1 = [ -85 85 ];
hold on
plot (x1,y1);
plot (x0,y0);
grid on
angle=45;
     angle_rad=((angle*2.*pi)./360);        
       [THETA,R] = cart2pol(x0,y0);
         THETA=THETA+angle_rad; %Add a_rad to theta
 [x0r,y0r] = pol2cart(THETA,R);
 plot(x0r,y0r);
 axis equal; %Rotated
 angle=45;
     angle_rad=((angle*2.*pi)./360); 
     [THETA,X] = cart2pol(x1,y1);%Convert to polar coordinates
     THETA=THETA+angle_rad; %Add a_rad to theta
      [x1r,y1r] = pol2cart(THETA,X); %Convert back to Cartesian coordinates
       plot(x1r,y1r);
       grid on
 hold off
  axis equal; %Rotated

[Prakash Choudhary]

I am Just a biggner so i creat the code with code with theta.

Answer 1

[Walter Roberson]

It is rotating. Look at the top of your plot.

The way to rotate relative to a point is to subtract the coordinates of the point to rotate around, do the rotation, then add the coordinates of the point to rotate around back in. If you want ot rotate around (800,0) then cart2pol(x1-800,y1) and plot(x1r+800,y1r)

[Prakash Choudhary]

It works, Thanks for your support!!