React native find closest location From user location - location

Question

i have array of location (cities) and i want to find from my current location nearest city from that array of location .
I'd like to test the distance between my user's locations against my array to see which location is the closest. How do I do this?

Answer 1

There is a pretty good documentation on how to calculate distance between two geo-location with Javascript examples that you can find here.
Calculate distance, bearing and more between Latitude/Longitude points
This page presents a variety of calculations for lati­tude/longi­tude
points, with the formulæ and code fragments for implementing them.
All these formulæ are for calculations on the basis of a spherical
earth (ignoring ellipsoidal effects) – which is accurate enough* for
most purposes… [In fact, the earth is very slightly ellipsoidal; using
a spherical model gives errors typically up to 0.3%1 – see notes for
further details].
Assuming you have an array with the geo-locations of the cities, you can loop through and calculate the distance against the current location of the user you get with the Geolocation API of react-native.

Answer 2

Assuming you have the data as an array of array/ object. For the demo code I am using array of array.
const cities = [
["city1", 10, 50, "blah"],
["city2", 40, 60, "blah"],
["city3", 25, 10, "blah"],
["city4", 5, 80, "blah"]
];
deg2Rad = (deg) => {
return deg * Math.PI / 180;
}
pythagorasEquirectangular = (lat1, lon1, lat2, lon2) => {
lat1 = this.deg2Rad(lat1);
lat2 = this.deg2Rad(lat2);
lon1 = this.deg2Rad(lon1);
lon2 = this.deg2Rad(lon2);
const R = 6371;
const x = (lon2 - lon1) * Math.cos((lat1 + lat2) / 2);
const y = (lat2 - lat1);
const d = Math.sqrt(x * x + y * y) * R;
return d;
}
nearestCity = (latitude, longitude) => {
let mindif = 99999;
let closest;
for (index = 0; index < cities.length; ++index) {
const dif = this.pythagorasEquirectangular(latitude, longitude, cities[index][1],
cities[index][2]);
if (dif < mindif) {
closest = index;
mindif = dif;
}
return cities[closest]
}
or something like this. Also you can get the current location using Geolocation.
Call nearestCity(lat, lon) with your current lat, lon.
Hope this helps.

Answer 3

This method has already been used in a previous reaction, unfortunately it was not suitable for React Native. I have edited the code so that it works on React Native.
The code is as follows:
cities = [
["city1", 10, 50, "blah"],
["city2", 40, 60, "blah"],
["city3", 25, 10, "blah"],
["city4", 5, 80, "blah"]
];
nearestPlace = null;
deg2Rad = (deg) => {
return deg * Math.PI / 180;
}
pythagorasEquirectangular = (lat1, lon1, lat2, lon2) => {
lat1 = this.deg2Rad(lat1);
lat2 = this.deg2Rad(lat2);
lon1 = this.deg2Rad(lon1);
lon2 = this.deg2Rad(lon2);
const R = 6371;
const x = (lon2 - lon1) * Math.cos((lat1 + lat2) / 2);
const y = (lat2 - lat1);
const d = Math.sqrt(x * x + y * y) * R;
return d;
}
nearestCity = (latitude, longitude) => {
let mindif = 99999;
let closest;
for (let index = 0; index < this.cities.length; index++) {
const dif = this.pythagorasEquirectangular(latitude, longitude, this.cities[index][1],
this.cities[index][2]);
if (dif < mindif) {
closest = index;
mindif = dif;
}
}
this.nearestPlace = closest
}
So when you then this.nearestCity (yourLat, yourLon) you will find the result in this.nearestPlace.

Answer 4

You can just use other package to calculate distance, like https://github.com/cmoncrief/geodist
Then you can calculate distance between two point by code
var geodist = require('geodist')
var dist = geodist({lat: 41.85, lon: -87.65}, {lat: 33.7489, lon: -84.3881})
console.log(dist)
// => 587