How to draw a perpendicular line to another?

Hello,

Suppose i have a segment S1 defined by 2 points (x01,z01) and (x02, z02). The center of the segment is defines as (xm0, zm0). I want to plot the perpendicular line PL1 to S1 at (xm0, zm0) and find the intersection point of PL1 and the axis Y=0. The code is detailed below

a1=(z01-z02)/(x01-x02); %z1=a1*x1+b1 b1=z01-a1*x01; a2=-1/a1; % z2 perp to z1--> a2=-1/a1 b2=zm0-a2*xm0; %z2=a2*x2+b2

x=xm0:0.1:10; z2=a2*x+b2; xi=-b2/a2; %solve 0=a2*xi+b2 zi=a2*xi+b2;

h3=line([xm0,xi],[zm0,zi]); %trace du rayon principal

However, when i check the angle between my 2 perpendicular lines, it appears that it's not pi/2

O=(a2-a1)/(1-a1*a2); alpha=atan(O)*180/pi;

Any ideas please?

Fatzo

Answer 1

[Iain]

 xm0 = (x01+x02)/2; ym0 = (y01+y02)/2
 m = (y2 - y1) / (x2-x1);
 PLm = tan( atan(m)+pi/2); 
 PLc = ym0 - PLm*xm0;
 %PL line eqn =  y_PL = PLm * x_PL + PLc
 x_at_yequalto0 = -PLc/PLm;

[hadis ensafi]

Hello.. thanks for your code.. I have this problem in 3D space! how can I calculate a perpendicular of a line in 3D space and in Specified plane? thanks a lot..