My Math Forum Calculate point coordinates within a circle

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 February 4th, 2012, 11:28 AM #1 Newbie   Joined: Feb 2012 Posts: 5 Thanks: 0 Calculate point coordinates within a circle Hi all, I am trying to figure out the coordinates of a point within a circle. I have an IR sensor which gives readings from 0 to 800. 800 meaning there are no objects in sight. What I want to do is make a miniture radar representation. I will have a turntable which will rotate the IR sensor while it scans for obstacles. Now, if it were a stationary IR sensor I'd know exactly where the object is - it would be whatever the sensor value returned because it would represent the Y axis... But, how would I work out the X and Y values for this point now that the IR sensor is rotating? I've drawn a diagram to help illustrate: Does anyone know the math to work this out?
 February 4th, 2012, 12:17 PM #2 Member   Joined: Feb 2012 Posts: 36 Thanks: 0 Re: Calculate point coordinates within a circle Convert the angle to radians and x=rcos(angle), y=rsin(angle)
 February 4th, 2012, 12:33 PM #3 Newbie   Joined: Feb 2012 Posts: 5 Thanks: 0 Re: Calculate point coordinates within a circle Ok, so after obtaining the X and Y, I could just subtract the distance of the object to the center from both values to give me the true value, correct?
February 4th, 2012, 12:34 PM   #4
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Re: Calculate point coordinates within a circle

Quote:
 Originally Posted by rich2020 Ok, so after obtaining the X and Y, I could just subtract the distance of the object to the center from both values to give me the true value, correct?
I meant "distance of the object FROM the center of the circle" - can't edit posts? :/

 February 4th, 2012, 12:38 PM #5 Member   Joined: Feb 2012 Posts: 36 Thanks: 0 Re: Calculate point coordinates within a circle Yep, basic coordinate pythagoras to locate the point in relation to the required limit of the sensor.
 February 4th, 2012, 12:39 PM #6 Newbie   Joined: Feb 2012 Posts: 5 Thanks: 0 Re: Calculate point coordinates within a circle Thanks very much for your help.
 February 4th, 2012, 04:57 PM #7 Newbie   Joined: Feb 2012 Posts: 5 Thanks: 0 Re: Calculate point coordinates within a circle Hmm... I don't think your way was correct. I needed to find the coordinates based on the angle and the distance an object. What I did was: X=Cos(A) * Distance Y=Sin(A) * Distance I used degrees, not radians. Then, because my circle (radius of 15mm) will be far smaller as it will be on a mobile Android device's screen, I did this: Sensor range is 800mm... so X = X/(800/15) Y = Y/(800/15) Correct me if I'm wrong please. I need this for a software project.

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