====== Distance Between Two Points On Earth ======

===== UTM =====

UTM (Universal Transverse Mercator) co-ordinates are an approximate mapping from the Earth's surface to flat regions. If your co-ordinates are in UTM then you can use pythagoras to calculate the distance between points:

<code>
distance = sqrt( (x1 - x2)^2 + (y1 - y2)^2 )
</code>

* [[http://en.wikipedia.org/wiki/Universal_Transverse_Mercator_coordinate_system]]

===== Latitude and Longitude =====

The distance between two sets of latitude and longitude co-ordinates are more interesting. The Haversine formula is a beautiful way to calculate these, combining both simplicity and accuracy over small distances:

<code>
dlon = lon2 - lon1
dlat = lat2 - lat1
a = sin^2(dlat/2) + cos(lat1) * cos(lat2) * sin^2(dlon/2)
c = 2 * arcsin(min(1,sqrt(a)))
d = R * c
</code>

* [[http://www.movable-type.co.uk/scripts/gis-faq-5.1.html]]
* [[http://en.wikipedia.org/wiki/Haversine_formula]]

-----
Tarim / March 2008 / for Swarm MediaSandbox project