### Author Topic: Math: Finding a point that is perpendicular to another point.  (Read 2055 times)

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#### aaranaf

• Newbie
• Posts: 4
##### Math: Finding a point that is perpendicular to another point.
« on: August 03, 2013, 01:23:52 am »
So here's what I want to do. I want to find the point in 2d-space for C.
I have the point A and B and the distance from B to C.
I know C is perpendicular to B. If someone could point me in the right direction on this it would be greatly appreciated.

#### The Hatchet

• Full Member
• Posts: 135
##### Re: Math: Finding a point that is perpendicular to another point.
« Reply #1 on: August 03, 2013, 02:08:38 am »
Go to google and put in "find point perpendicular to line"

#### rgrant1993

• Newbie
• Posts: 12
##### Re: Math: Finding a point that is perpendicular to another point.
« Reply #2 on: August 03, 2013, 08:25:55 pm »
We need to know the data you have recorded inorder to know the data we need to find.

#### Grimshaw

• Hero Member
• Posts: 631
• Nephilim SDK
##### Re: Math: Finding a point that is perpendicular to another point.
« Reply #3 on: August 03, 2013, 08:37:41 pm »
(direction from A to B)
V = B - A
V' = normalize(V)

(vector orthogonal to V' - perpendicular)
O = (-V'y, V'x)

(finally find point C by going from B in the orthogonal direction)
C = B + O * distance

I am a little fuzzy right now but if something is wrong here ill get back to you

#### gostron

• Jr. Member
• Posts: 53
##### Re: Math: Finding a point that is perpendicular to another point.
« Reply #4 on: August 05, 2013, 01:02:44 pm »
May I add that knowing the distance and that it's perpendicular gives your two points, one for each side.

for a vector defined by (a,b) an orthogonal vector would be (-b, a) (so I do agree with Grimshaw, just to say it a bit differently)