We help IT Professionals succeed at work.

New podcast episode! Our very own Community Manager, Rob Jurd, gives his insight on the value of an online community. Listen Now!

x

angle in a circle

812 Views
Last Modified: 2013-12-26
 markww    Member since: 4/5/2007
 
 Posted - 10/13/2007 2:19:29 PM
Hi,

I have a circle, I know its radius. I have a point on its edge. Is there anyway to figure out what angle in degrees that is?


                |
        ------|----
      /         |        \    
     P         |         \  
     |          |           |
 ----------O-------X--------          
     |          |           |
      \         |         /
       \------|---- /
                |
           |

yeah that's a fine ascii circle, so anyway, I'm interested in the angle formed between P, O, X. I know the coordinates of all 3, I just want to know the angle between them.

Thanks for any help

p.s. - the formatting keeps messing up the circle (not that it was that great to begin with, hope it's understandable)
Comment
Watch Question

Unlock this solution and get a sample of our free trial.
(No credit card required)
UNLOCK SOLUTION
ozo
CERTIFIED EXPERT
Most Valuable Expert 2014
Top Expert 2015

Commented:
in  general arccos( (X-O) dot (P-O) / (|X-O| * |P-O|) )

Commented:
Use your cordinates to determine the length of the intercepted arc between p and x. The angle in radians = the length of the arc / the length of the radius.  The formula found in my Trig book is omega = s / r.  Then convert radians to degrees with 2 pi radians = 360 degree (circumference of a circle).

I don't remember and not able to quickly find how to get the length of the arc segement.  Will let you know if I find out.  Please give details of the coordinates and other information you have about this problem.
ozo
CERTIFIED EXPERT
Most Valuable Expert 2014
Top Expert 2015

Commented:
You can find the arc from the cosine of the dot product
ozo
CERTIFIED EXPERT
Most Valuable Expert 2014
Top Expert 2015

Commented:
http://en.wikipedia.org/wiki/Dot_product#Geometric_interpretation
If you already know |a| = |b| = radius then you only need a ยท b
Unlock the solution to this question.
Thanks for using Experts Exchange.

Please provide your email to receive a sample view!

*This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply.

OR

Please enter a first name

Please enter a last name

8+ characters (letters, numbers, and a symbol)

By clicking, you agree to the Terms of Use and Privacy Policy.