Determine if a Longitude & Latitude Co-ordinate is Inside a Radius in Miles and Kilometers

Question

Using only pseudo-code or JavaScript, can anyone describe the best way to determine which items in array of objects composed of:

{
"lat": float,
"lng": float
}

are within a given radius in either miles or kilometers?

I am adding geo-location-based queries to ForerunnerDB (https://github.com/irrelon/ForerunnerDB) and would like to be able to produce fast results from the search.

Bonus points if you can describe an indexing strategy that will speed up the query over the array. I have written the ForerunnerDB database from the ground up so can be flexible with integrating the answer into the code, but the main concern is query performance.

While the question pertains to a new feature of ForerunnerDB, it does not require that you go and read that project's source or familiarise yourself with that system and a pseudo-code or stand-alone JS example would be very welcome!

This could be rather complicated, since geographical points are 3-dimensional. — wvdz, Apr 16 '14 at 16:49
Can't this question simply be rephrased to: how do I calculate the distance between two geographical points? — wvdz, Apr 16 '14 at 16:52

score 4 · Accepted Answer · edited Jul 22 '21 at 02:45

Here is a simple "direct" approach using Haversine formula:

//This function takes in latitude and longitude of two locations
// and returns the distance between them as the crow flies (in meters)
function calcCrow(coords1, coords2)
{
  // var R = 6.371; // km
  var R = 6371000;
  var dLat = toRad(coords2.lat-coords1.lat);
  var dLon = toRad(coords2.lng-coords1.lng);
  var lat1 = toRad(coords1.lat);
  var lat2 = toRad(coords2.lat);

  var a = Math.sin(dLat/2) * Math.sin(dLat/2) +
    Math.sin(dLon/2) * Math.sin(dLon/2) * Math.cos(lat1) * Math.cos(lat2); 
  var c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1-a)); 
  var d = R * c;
  return d;
}

// Converts numeric degrees to radians
function toRad(Value)
{
    return Value * Math.PI / 180;
}

I believe this code might have come from here: Function to calculate distance between two coordinates shows wrong

The only optimisation I see is adding tangents for both latitude and longitude to cut out the results that are far outside the search region.

P.S. I really like ForerunnerDB and can't wait to see geo-related functionality

This is a real solution. You saved my day +1 – Pankaj Parkar Jun 13 '20 at 09:11 — Pankaj Parkar, Jun 13 '20 at 09:11

score 0 · Answer 2 · edited May 23 '17 at 12:07

0

I suppose this would be answered more or less in How do I calculate distance between two latitude-longitude points?

Anyway, it might be easier to use ready made APIs such as HERE Maps API's geo-coordinate class, than creating the calculating functionality by yourself.

edited May 23 '17 at 12:07

Community

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answered Apr 16 '14 at 18:28

Dr.Jukka

2,346
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Agree that it is always easier to use a third party but that is not really the point of the exercise. The database I am writing must have this functionality built in and I must understand the code so that I can make optimisations and changes later – Rob Evans May 18 '14 at 18:15

Determine if a Longitude & Latitude Co-ordinate is Inside a Radius in Miles and Kilometers

2 Answers2

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