To compute the physical distance between landmarks I am looking up the Lat and Long from in sites.xml and then using from the Lats and Longs of two locations we can use this tool to compute the distance [http://www.movable-type.co.uk/scripts/latlong.html}.
Below is a perl sub you could embed in a perl script. It assumes you have a min RTT and the lat longs of source and destination. You could also extract the code to calculate the distance.
...