title: How to find relative angle from one gps coordinate vector to other?
body: <p>I have extracted a set of three coordinates and I want to find the relative angles between their two vectors.</p>
  
  <ul>
  <li>P1: <code>57.3112, 25.24871</code></li>
  <li>C1: <code>57.31105, 25.24875</code></li>
  <li>T1: <code>57.31086, 25.24803</code></li>
  </ul>
  
  <p>Like: <code>V1 = C1 - P1</code>, <code>V2 = T1 - C1</code> and then get angle from <code>V1</code> to <code>V2</code>.</p>
  
  <p>But I am afraid that cartesian functions won't cut it here, because in actual application, the coordinates could span different latitudes and longitudes.</p>
  
  <p>I have searched google but the functions I have seen, do not convince me. I also tried some in my app, but the returned angles didn't return the expected results.</p>
  
  <p>For these three points, deducing visually, I expect the angle to be somewhere around 120-140 degrees.</p>
  
  <p>I have limited knowledge in geographic calculations and I'm out of clues here.</p>
  
  <p>How do I calculate the angle?</p>