How to run a geo "nearby" query with firestore?
UPDATE: Firestore does not support actual GeoPoint queries at present so while the below query executes successfully, it only filters by latitude, not by longitude and thus will return many results that are not nearby. The best solution would be to use geohashes. To learn how to do something similar yourself, have a look at this video.
This can be done by creating a bounding box less than greater than query. As for the efficiency, I can't speak to it.
Note, the accuracy of the lat/long offset for ~1 mile should be reviewed, but here is a quick way to do this:
SWIFT 3.0 Version
func getDocumentNearBy(latitude: Double, longitude: Double, distance: Double) {
// ~1 mile of lat and lon in degrees
let lat = 0.0144927536231884
let lon = 0.0181818181818182
let lowerLat = latitude - (lat * distance)
let lowerLon = longitude - (lon * distance)
let greaterLat = latitude + (lat * distance)
let greaterLon = longitude + (lon * distance)
let lesserGeopoint = GeoPoint(latitude: lowerLat, longitude: lowerLon)
let greaterGeopoint = GeoPoint(latitude: greaterLat, longitude: greaterLon)
let docRef = Firestore.firestore().collection("locations")
let query = docRef.whereField("location", isGreaterThan: lesserGeopoint).whereField("location", isLessThan: greaterGeopoint)
query.getDocuments { snapshot, error in
if let error = error {
print("Error getting documents: \(error)")
} else {
for document in snapshot!.documents {
print("\(document.documentID) => \(document.data())")
}
}
}
}
func run() {
// Get all locations within 10 miles of Google Headquarters
getDocumentNearBy(latitude: 37.422000, longitude: -122.084057, distance: 10)
}
A new project has been introduced since @monkeybonkey first ask this question. The project is called GEOFirestore.
With this library you can perform queries like query documents within a circle:
const geoQuery = geoFirestore.query({
center: new firebase.firestore.GeoPoint(10.38, 2.41),
radius: 10.5
});
You can install GeoFirestore via npm. You will have to install Firebase separately (because it is a peer dependency to GeoFirestore):
$ npm install geofirestore firebase --save
UPDATE: Firestore does not support actual GeoPoint queries at present so while the below query executes successfully, it only filters by latitude, not by longitude and thus will return many results that are not nearby. The best solution would be to use geohashes. To learn how to do something similar yourself, have a look at this video.
(First let me apologize for all the code in this post, I just wanted anyone reading this answer to have an easy time reproducing the functionality.)
To address the same concern the OP had, at first I adapted the GeoFire library to work with Firestore (you can learn a lot about geo-stuff by looking at that library). Then I realized I didn't really mind if locations were returned in an exact circle. I just wanted some way to get 'nearby' locations.
I can't believe how long it took me to realize this, but you can just perform a double inequality query on a GeoPoint field using a SW corner and NE corner to get locations within a bounding box around a center point.
So I made a JavaScript function like the one below (this is basically a JS version of Ryan Lee's answer).
/**
* Get locations within a bounding box defined by a center point and distance from from the center point to the side of the box;
*
* @param {Object} area an object that represents the bounding box
* around a point in which locations should be retrieved
* @param {Object} area.center an object containing the latitude and
* longitude of the center point of the bounding box
* @param {number} area.center.latitude the latitude of the center point
* @param {number} area.center.longitude the longitude of the center point
* @param {number} area.radius (in kilometers) the radius of a circle
* that is inscribed in the bounding box;
* This could also be described as half of the bounding box's side length.
* @return {Promise} a Promise that fulfills with an array of all the
* retrieved locations
*/
function getLocations(area) {
// calculate the SW and NE corners of the bounding box to query for
const box = utils.boundingBoxCoordinates(area.center, area.radius);
// construct the GeoPoints
const lesserGeopoint = new GeoPoint(box.swCorner.latitude, box.swCorner.longitude);
const greaterGeopoint = new GeoPoint(box.neCorner.latitude, box.neCorner.longitude);
// construct the Firestore query
let query = firebase.firestore().collection('myCollection').where('location', '>', lesserGeopoint).where('location', '<', greaterGeopoint);
// return a Promise that fulfills with the locations
return query.get()
.then((snapshot) => {
const allLocs = []; // used to hold all the loc data
snapshot.forEach((loc) => {
// get the data
const data = loc.data();
// calculate a distance from the center
data.distanceFromCenter = utils.distance(area.center, data.location);
// add to the array
allLocs.push(data);
});
return allLocs;
})
.catch((err) => {
return new Error('Error while retrieving events');
});
}
The function above also adds a .distanceFromCenter property to each piece of location data that's returned so that you could get the circle-like behavior by just checking if that distance is within the range you want.
I use two util functions in the function above so here's the code for those as well. (All of the util functions below are actually adapted from the GeoFire library.)
distance():
/**
* Calculates the distance, in kilometers, between two locations, via the
* Haversine formula. Note that this is approximate due to the fact that
* the Earth's radius varies between 6356.752 km and 6378.137 km.
*
* @param {Object} location1 The first location given as .latitude and .longitude
* @param {Object} location2 The second location given as .latitude and .longitude
* @return {number} The distance, in kilometers, between the inputted locations.
*/
distance(location1, location2) {
const radius = 6371; // Earth's radius in kilometers
const latDelta = degreesToRadians(location2.latitude - location1.latitude);
const lonDelta = degreesToRadians(location2.longitude - location1.longitude);
const a = (Math.sin(latDelta / 2) * Math.sin(latDelta / 2)) +
(Math.cos(degreesToRadians(location1.latitude)) * Math.cos(degreesToRadians(location2.latitude)) *
Math.sin(lonDelta / 2) * Math.sin(lonDelta / 2));
const c = 2 * Math.atan2(Math.sqrt(a), Math.sqrt(1 - a));
return radius * c;
}
boundingBoxCoordinates(): (There are more utils used in here as well that I've pasted below.)
/**
* Calculates the SW and NE corners of a bounding box around a center point for a given radius;
*
* @param {Object} center The center given as .latitude and .longitude
* @param {number} radius The radius of the box (in kilometers)
* @return {Object} The SW and NE corners given as .swCorner and .neCorner
*/
boundingBoxCoordinates(center, radius) {
const KM_PER_DEGREE_LATITUDE = 110.574;
const latDegrees = radius / KM_PER_DEGREE_LATITUDE;
const latitudeNorth = Math.min(90, center.latitude + latDegrees);
const latitudeSouth = Math.max(-90, center.latitude - latDegrees);
// calculate longitude based on current latitude
const longDegsNorth = metersToLongitudeDegrees(radius, latitudeNorth);
const longDegsSouth = metersToLongitudeDegrees(radius, latitudeSouth);
const longDegs = Math.max(longDegsNorth, longDegsSouth);
return {
swCorner: { // bottom-left (SW corner)
latitude: latitudeSouth,
longitude: wrapLongitude(center.longitude - longDegs),
},
neCorner: { // top-right (NE corner)
latitude: latitudeNorth,
longitude: wrapLongitude(center.longitude + longDegs),
},
};
}
metersToLongitudeDegrees():
/**
* Calculates the number of degrees a given distance is at a given latitude.
*
* @param {number} distance The distance to convert.
* @param {number} latitude The latitude at which to calculate.
* @return {number} The number of degrees the distance corresponds to.
*/
function metersToLongitudeDegrees(distance, latitude) {
const EARTH_EQ_RADIUS = 6378137.0;
// this is a super, fancy magic number that the GeoFire lib can explain (maybe)
const E2 = 0.00669447819799;
const EPSILON = 1e-12;
const radians = degreesToRadians(latitude);
const num = Math.cos(radians) * EARTH_EQ_RADIUS * Math.PI / 180;
const denom = 1 / Math.sqrt(1 - E2 * Math.sin(radians) * Math.sin(radians));
const deltaDeg = num * denom;
if (deltaDeg < EPSILON) {
return distance > 0 ? 360 : 0;
}
// else
return Math.min(360, distance / deltaDeg);
}
wrapLongitude():
/**
* Wraps the longitude to [-180,180].
*
* @param {number} longitude The longitude to wrap.
* @return {number} longitude The resulting longitude.
*/
function wrapLongitude(longitude) {
if (longitude <= 180 && longitude >= -180) {
return longitude;
}
const adjusted = longitude + 180;
if (adjusted > 0) {
return (adjusted % 360) - 180;
}
// else
return 180 - (-adjusted % 360);
}