Geo calculations

Rails
1

Hi,

does anyone know a gem / plugin / class with methods to do calculations
based on lat/lon coordinates? E.g. calculate the distance of 2 points on
the earth surface. I tried to implement my own stuff, which does not
quite give me exact results.

thx,
Robert

2

Hi Robert

does anyone know a gem / plugin / class with methods to do calculations

based on lat/lon coordinates? E.g. calculate the distance of 2 points on
the earth surface. I tried to implement my own stuff, which does not
quite give me exact results.

(quite a repost from a recent railsfrance ML thread, sorry for people
subscribing to both lists)

Not specifically a gem for the moment, but you may find the information
useful though.

Are you trying to compute bird-flight distances, or driving distances ?

for bird-flight distances:

for driving distances it’s more complicated (and google API doesn’t
expose
this functionaly AFAIK, although it’s available in maps.google.com

hope this helps

Thibaut

3

There are various mathematical formulae that do this.
Here’ s pretty good (if slightly dense) list of them:
http://www.movable-type.co.uk/scripts/LatLong.html

I use the cosine method (via a MySQL query – MySQL has distance as one
of the spatial functions, but it doesn’t come up with the right answers
– assumes the earth is flat, I think; PotGis might be better) and it
seems to work pretty well.

You should also check out ym4r and georuby (at
http://www.thepochisuperstarmegashow.com/)

HTH

CT

4

Hi Thibaut,

thanks for the hints, I will evaluate those. I need bird-flight
distances for a distance-limited search function.

Robert