<slide>
<title>Finding the direction</title>
<iframe width="1000" align="center" height="200" filename='examples/3angle/?l=gc&amp;lon=:-:lon:-:&amp;lat=:-:lat:-:&amp;zoom=4'/>

<blurb>Formula:</blurb>
<example>
θ = atan2(
    sin(Δλ).cos(φ2),
    cos(φ1).sin(φ2) − sin(φ1).cos(φ2).cos(Δλ)
)
</example>

<blurb>Implemented in php-geospatial:</blurb>
<blurb>https://github.com/php-geospatial/geospatial/blob/master/geospatial.c#L623</blurb>
</slide>
