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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  
Newbie Joined: Feb 2012 Posts: 5 Thanks: 0  Re: Calculate point coordinates within a circle Quote:
 
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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calculate, circle, coordinates, point 
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