Drawing a perpindecular line in XY coordinate system

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butterbr0..

Drawing a perpindecular line in XY coordinate system

in General Discussion • Other • 1 year ago

Hey,

i am trying to draw a perpindecular line to some existing line, like shown below:

I start with two points A and B that form a line, and calculate point C like so:
C.x = (A.x + B.x) / 2;
C.y = (A.y + B.y) / 2;

Now how could I calculate D?
I know I could just draw my line again and rotate it by 90° degrees but I would like to get it working without this little cheat ;)
Any help really appreciated, I guess its not that hard but I dont see it ...

Cheers

Replies(6)

tfguy44

Re: Drawing a perpindecular line in XY coordinate system

1 year ago

Rotating by 90 degrees is easy - rotating by any other number of degrees is not.
Notice that the difference between Ax and Bx is the same as the difference between Cy and Dy.
Notice that the difference between Ay and By is the same as the difference between Cx and Dx.

so
Dx = Cx + Ay - By
Dy = Cy + Ax - Bx

butterbr0..

Re: Drawing a perpindecular line in XY coordinate system

1 year ago

Hey thanks, thats a great hint!
Am I right that this is only true, when the line CD is of the same length as line AB? I just copied the first line for the image and rotated it heh :P
Now how would I go in Processing if I want my line to be shorter or longer, maybe as long as it needs to hit the border of the frame?

butterbr0..

Re: Drawing a perpindecular line in XY coordinate system

1 year ago

For some reasons it worked using:

Dx = Cx + By - Ay (instead of Ay - By)
Dy = Cy + Ax - Bx

hm Oo"

Now how could i take my line CD and lengthen it? In essence how to move D further along its current direction? Sorry I am new to all this vector things.

tfguy44

Re: Drawing a perpindecular line in XY coordinate system

1 year ago

draw the line between your point C and a new point E instead, where:

Ex = Cx + (L * (By - Ay))
Ey = Cy + (L * (Ax - Bx))

Where L is some constant number.

butterbr0..

Re: Re: Drawing a perpindecular line in XY coordinate system

1 year ago

late but better than never: thanks!!

patakk

Re: Drawing a perpindecular line in XY coordinate system

1 year ago

void setup() {
size(700, 700);
background(255);
stroke(0);
smooth();
}
float x1, y1, x2, y2, x3, y3, x4, y4;
float k1, k2, angle;
float len = 180; // the second line's length
void draw() {
background(255);
x1 = width/2;
y1 = height/2;
x2 = mouseX;
y2 = mouseY;
k1 = (y2-y1)/(x1-x2);
line(x1, y1, x2, y2);
x3 = (x1+x2)/2;
y3 = (y1+y2)/2;
angle = atan2(y2-y1, x2-x1);
if (degrees(angle)<0)
angle = radians(360+degrees(angle));
angle = angle + radians(90);
line(x3, y3, x3 + len*cos(angle), y3 + len*sin(angle));
}

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