how to calculate the distance between two coodinates

[Chen Chen]

Hi everyone,

Did u use owntracks on node-red? i would like to calculate the distance between two owntracks users but don't know what can i write in the function.

[chris mobberley]

Hi,

http://flows.nodered.org/ - Contains a few exmaples of using own-tracks via MQTT. I know of atleast one flow on there which uses geofence and would probably be an excellent starting point for this.

http://flows.nodered.org/flow/ab31cd939f2e73503fb0 <-- Specific example - The function nodes are probably most interesting for you on there.

[Ang Eleanor]

@chrismobberley

Hi, we are looking for any java programming codes that can actually help us to calculate the two distance of owntracks when they are away from each other using the function node.

[Mark Setrem]

Have you tried using Google?

The maths to calculate the distance between two pairs of lat long coordinates is fairly straight forward and easily found online.  As Chris says there are several flows within http://flows.nodered.org that should help you in how to structure the flow.

One thing you will need to do is store the values of one pair of lat, longs and trigger the calculation when the other pair arrives.

There are examples of doing this in the forum.

[Claudiu O]

If you are looking for Java code, you could use this library: https://code.google.com/p/simplelatlng/ It is not mine, just something I found and used in the past with great results.

[TJ Koury]

You're looking for this:

http://en.wikipedia.org/wiki/Haversine_formula

Implemented like this:

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

Simplified like this:

dlon = lon2 - lon1 
dlat = lat2 - lat1 
a = (sin(dlat/2))^2 + cos(lat1) * cos(lat2) * (sin(dlon/2))^2 
c = 2 * atan2( sqrt(a), sqrt(1-a) ) 
d = R * c (where R is the radius of the Earth)

(from http://andrew.hedges.name/experiments/haversine/).

[Dave C-J]

If this is for a Node-RED function then you will want javascript not java.... 

and Google is your friend - try searching for

    javascript distance between lat lon