July 5th, 2017, 02:48 AM  #1 
Newbie Joined: Jun 2017 From: italia Posts: 9 Thanks: 1  How many rounds?
A particle is moving along a circle CCW with almost constant speed. I sample the x and y coordinates of the particle to get a point every degree or so (usually 1 point every 0.5 to 1.5 degrees). Since I need to stop the sampling after a given number of rounds, I need to count how many rounds the particle has done so far. 
July 5th, 2017, 03:41 AM  #2 
Global Moderator Joined: Dec 2006 Posts: 18,951 Thanks: 1599 
Do you mean you want to count the number of completed rounds?

July 5th, 2017, 05:24 AM  #3 
Newbie Joined: Jun 2017 From: italia Posts: 9 Thanks: 1 
Yep! (Sorry for my English.)

July 5th, 2017, 10:25 AM  #4 
Senior Member Joined: Aug 2012 Posts: 1,886 Thanks: 522 
If the motion is always in the same direction, you can tell that it's gone around once when it appears to go backwards. In other words if the angle (between the ray from the origin to your point, and the positive xaxis) decreases. In other words if the angle is 45 degrees on one measurement and 44 degrees on the next, it must have gone around 359 degrees. 

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