Filter locations in an area of X km

Question

I am trying to set up a small project where I have a list of locations and can filter them according to a x km amount. Ex: Filter all places within a 5km radius of my current location.

I have a Json with some places in my city and when I try to make a 2km filter the Json returns blank, but if I step 50km as parameter all data is returned. I am not able to identify where I am missing.

Follows excerpt from the code:

var mongoose = require('mongoose');
var Location = mongoose.model('Location');

// create an export function to encapsulate the controller's methods
module.exports = {
  index: function(req, res, next) {
    res.json(200, {
      status: 'Location API is running.',
    });
  },
  findLocation: function(req, res, next) {
    var limit = req.query.limit || 10;

    // get the max distance or set it to 8 kilometers
    var maxDistance = req.query.distance || 8;

    // we need to convert the distance to radians
    // the raduis of Earth is approximately 6371 kilometers
    maxDistance /= 6371;

    // get coordinates [ <longitude> , <latitude> ]
    var coords = [];
    coords[0] = req.query.longitude || 0;
    coords[1] = req.query.latitude || 0;

    // find a location
    Location.find({
      loc: {
        $near: coords,
        $maxDistance: maxDistance
      }
    }).limit(limit).exec(function(err, locations) {
      if (err) {
        return res.json(500, err);
      }
      res.json(200, locations);
    });
  }
};

That’s the Json that I’m using:

[
  {
    "name": "Igreja Matriz",
    "loc": [
      -49.974762,
      -23.160631

    ]
  },
  {
    "name": "Prefeitura Jacarezinho",
    "loc": [
      -49.973597,
      -23.159745
    ]
  },
  {
    "name": "Lotérica",
    "loc": [
      -49.980461,
      -23.164231
    ]
  }
]

I pass the parameters by QueryString thus: http://localhost:3000/api/locations?longitude=-49.978440&latitude=-23.169557&distance=2

Console and result:

How I get the desired result?

Answer 1

The error in question is acceptable in view of the working scale and the reference system used. An alternative to increase the accuracy of the radius, if its study area fits in a spindle, would be to use the UTM projection system. That way the reported lightning will actually be in meters.

You can also use a geographic database, such as Postgresql/Postgis, which solves this type of situation easily. Your query would work as follows:

-- para um raio de 50 km = 50.000 m:
SELECT ST_Buffer(geom::geography,50000) AS geom
FROM nome_tabela
WHERE condicao;

I’ll give you some links on the subject:

Postgis - Geometry or Geography find points Within Distance in meters

Postgis: extraction of measurements in tables with geographical coordinates

Postgis - When to use Geography Data type over Geometry data type

I hope I’ve cooperated :)