**USING GPS**

**Converting GPS to Distance**

**Parallax GPS Module PMB-648**

**http://www.movable-type.co.uk/scripts/latlong.html**

Equirectangular approximationIf performance is an issue and accuracy less important, for small distances Pythagoras’ theorem can be used on an equirectangular projection:*

**Formula**

x = Δλ.cos(φ)

y = Δφ

d = R.√x² + y²

**JavaScript:**

var x = (lon2-lon1) * Math.cos((lat1+lat2)/2);

var y = (lat2-lat1);

var d = Math.sqrt(x*x + y*y) * R;

*(lat/lon in radians!)*This uses just one trig and one sqrt function – as against half-a-dozen trig functions for cos law, and 7 trigs + 2 sqrts for haversine. Accuracy is somewhat complex: along meridians there are no errors, otherwise they depend on distance, bearing, and latitude, but are small enough for many purposes* (and often trivial compared with the spherical approximation itself).