CODEWITHSUNDEEP
javascriptgoogle-mapsgoogle-maps-api-3
A. L
A. L

Reputation: 12689

Google map getting the range of possible lat and lng from a point with a radius

So I'm trying to find what range of latitude and longitude values I can use when trying to find other points on a map from an origin position based on the radius (e.g. 5km).

Current I'm using the Haversine formula from Calculate distance between two points in google maps V3 to calculate how long 1m is in both latitude and longitude.

var rad = function(x) {
  return x * Math.PI / 180;
};

var getDistance = function(p1, p2) {
  var R = 6378137; // Earth’s mean radius in meter
  var dLat = rad(p2.lat - p1.lat);
  var dLong = rad(p2.lng - p1.lng);
  var a = Math.sin(dLat / 2) * Math.sin(dLat / 2) +
    Math.cos(rad(p1.lat)) * Math.cos(rad(p2.lat)) *
    Math.sin(dLong / 2) * Math.sin(dLong / 2);
  var c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a));
  var d = R * c;
  return d; // returns the distance in meter
}

let origin = {lat: 40, lng: 40}
let p1 = {lat: 41, lng: 40}
let p2 = {lat: 40, lng: 41}

let latDist = getDistance(origin, p1)
let lngDist = getDistance(origin, p2)

console.log(latDist, lngDist);

let lat1m = 1/latDist
let lng1m = 1/lngDist

console.log(lat1m, lng1m)

From this, 1m in latitude is roughly 0.000008983152841195214 and 1m in longitude is roughly 0.000011726734698319366. So 5km would just be 5000 multiplied by each of the points then plus/minus from the origin.

Was there a Google API to get possible ranges or is this the correct method?

Upvotes: 0

Views: 1544

Answers (1)

shukshin.ivan
shukshin.ivan

Reputation: 11340

UPD.

I was wrong, you can use google.maps.geometry.spherical.computeDistanceBetween (latLngA, latLngB); to calculate distance between two points. Docs. Just pass LatLng objects.

OLD JS ANSWER.

As for your question, you don't need to use Google API at all. In addition, Google API doesn't provide simple functions, that can be calculated using geometry.

Let me make your code a little simplier. Length of an arc is simply radius * angle in radians. So lat distance is latDist = R * dLat and lng distance is lngDist = R * dLng * Math.cos(rad(origin.lat)). If you calculate distances, smaller than thousand of kilometers, you can assume, that latitude is constant within the area, hence you don't need to use complex formula for that.

var rad = function(x) {
  return x * Math.PI / 180;
};

var R = 6378137; // Earth’s mean radius in meter
let origin = {lat: 40, lng: 40}

let latDist = R * rad(1)
let lngDist = R * rad(1) * Math.cos(rad(origin.lat))

console.log(latDist, lngDist);

let areaRadius = 1000; // in meters

let latitudeRangeDelta = areaRadius / latDist;
let longitudeRangeDelta = areaRadius / lngDist;

console.log('latitude of the area is within range [' + (origin.lat - latitudeRangeDelta) + ', ' + (origin.lat + latitudeRangeDelta) + ']')
console.log('longitude of the area is within range [' + (origin.lng - longitudeRangeDelta) + ', ' + (origin.lng + longitudeRangeDelta) + ']')

Upvotes: 2

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