# Trig problem

**URL:** https://forum.kirupa.com/t/trig-problem/320370
**Category:** programming
**Created:** [March 22, 2011, 1:16am UTC](https://forum.kirupa.com/t/trig-problem/320370 "2011-03-22T01:16:46Z")
**Posts on this page:** 1
**Page:** 1

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### Author: ![ColinDavies](https://avatars.discourse-cdn.com/v4/letter/c/94ad74/32.png) [@ColinDavies](https://forum.kirupa.com/u/ColinDavies)
#### Post date: [March 22, 2011, 1:16am UTC](https://forum.kirupa.com/t/trig-problem/320370/1 "2011-03-22T01:16:46Z")

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I’m hoping someone might have an easy answer here, also hoping this is the right forum.

I have a stage which is circular shaped plane,  
If my observer is at xb,yb on the and my object is at xc,yc  
I can easily find the distance from one to the other via Pythagorus,  
And to find the observers angle I reference the circles center as 0,0  
Atan2(deltaY,deltaX) will give me that angle.  
Thus we now have a triangle abc with point a being at the center of the circle.  
Considering the circle to have a radius of 1 Radian,  
How do I calculate the distance from the observer to the circles perimeter via the object?  
I need this to calculate the perspective,