Birçok uygulamada fiziksel konumlara göre dizine eklenen belgeler bulunur. Örneğin, uygulamanız kullanıcıların mevcut konumlarının yakınındaki mağazalara göz atmasına olanak tanıyabilir.
Çözüm: Coğrafi karma oluşturma
Coğrafi karma, bir (latitude, longitude)
çiftini tek bir Base32 dizesine kodlayan bir sistemdir. Geohash sisteminde dünya dikdörtgen bir ızgaraya bölünür.
Geohash dizesinin her karakteri, ön ek karmasının 32 alt bölümünden birini belirtir. Örneğin, abcd
coğrafi karması, daha büyük abc
coğrafi karmasının tamamına dahil olan 32 dört karakterli karmadan biridir.
İki karma oluşturma işlemi arasında paylaşılan önek ne kadar uzunsa bu işlemler birbirine o kadar yakındır. Örneğin, abcdef
, abcdeg
'a abcdff
'den daha yakındır. Ancak bunun tersi doğru değildir. İki alan birbirine çok yakın olsa da çok farklı coğrafi karma oluşturabilir:
Yalnızca tek bir dizine eklenen alan gerektirirken Cloud Firestore'te konuma göre belgeleri depolamak ve sorgulamak için coğrafi karma oluşturma işlemlerini kullanabiliriz.
Yardımcı kitaplığı yükleme
Coğrafi karma oluşturma ve ayrıştırma işlemi bazı karmaşık matematik işlemleri içerir. Bu nedenle, Android, Apple ve web'deki en zor bölümleri soyutlamak için yardımcı kitaplıklar oluşturduk:
Web
// Install from NPM. If you prefer to use a static .js file visit
// https://github.com/firebase/geofire-js/releases and download
// geofire-common.min.js from the latest version
npm install --save geofire-common
Web
// Install from NPM. If you prefer to use a static .js file visit
// https://github.com/firebase/geofire-js/releases and download
// geofire-common.min.js from the latest version
npm install --save geofire-common
Swift
Kotlin
// Add this to your app/build.gradle
implementation 'com.firebase:geofire-android-common:3.2.0'
Java
// Add this to your app/build.gradle
implementation 'com.firebase:geofire-android-common:3.1.0'
Mağaza coğrafi karmaları
Konuma göre dizine eklemek istediğiniz her doküman için bir Geohash alanı depolamanız gerekir:
Web
import { doc, updateDoc } from 'firebase/firestore'; // Compute the GeoHash for a lat/lng point const lat = 51.5074; const lng = 0.1278; const hash = geofire.geohashForLocation([lat, lng]); // Add the hash and the lat/lng to the document. We will use the hash // for queries and the lat/lng for distance comparisons. const londonRef = doc(db, 'cities', 'LON'); await updateDoc(londonRef, { geohash: hash, lat: lat, lng: lng });
Web
// Compute the GeoHash for a lat/lng point const lat = 51.5074; const lng = 0.1278; const hash = geofire.geohashForLocation([lat, lng]); // Add the hash and the lat/lng to the document. We will use the hash // for queries and the lat/lng for distance comparisons. const londonRef = db.collection('cities').doc('LON'); londonRef.update({ geohash: hash, lat: lat, lng: lng }).then(() => { // ... });
Swift
// Compute the GeoHash for a lat/lng point let latitude = 51.5074 let longitude = 0.12780 let location = CLLocationCoordinate2D(latitude: latitude, longitude: longitude) let hash = GFUtils.geoHash(forLocation: location) // Add the hash and the lat/lng to the document. We will use the hash // for queries and the lat/lng for distance comparisons. let documentData: [String: Any] = [ "geohash": hash, "lat": latitude, "lng": longitude ] let londonRef = db.collection("cities").document("LON") londonRef.updateData(documentData) { error in // ... }
Kotlin
// Compute the GeoHash for a lat/lng point val lat = 51.5074 val lng = 0.1278 val hash = GeoFireUtils.getGeoHashForLocation(GeoLocation(lat, lng)) // Add the hash and the lat/lng to the document. We will use the hash // for queries and the lat/lng for distance comparisons. val updates: MutableMap<String, Any> = mutableMapOf( "geohash" to hash, "lat" to lat, "lng" to lng, ) val londonRef = db.collection("cities").document("LON") londonRef.update(updates) .addOnCompleteListener { // ... }
Java
// Compute the GeoHash for a lat/lng point double lat = 51.5074; double lng = 0.1278; String hash = GeoFireUtils.getGeoHashForLocation(new GeoLocation(lat, lng)); // Add the hash and the lat/lng to the document. We will use the hash // for queries and the lat/lng for distance comparisons. Map<String, Object> updates = new HashMap<>(); updates.put("geohash", hash); updates.put("lat", lat); updates.put("lng", lng); DocumentReference londonRef = db.collection("cities").document("LON"); londonRef.update(updates) .addOnCompleteListener(new OnCompleteListener<Void>() { @Override public void onComplete(@NonNull Task<Void> task) { // ... } });
Coğrafi karma oluşturma işlemlerini sorgulayın
Coğrafi karmalar, coğrafi karma alanında bir dizi sorguyu birleştirip bazı yanlış pozitifleri filtreleyerek alan sorgularını yaklaşık olarak tahmin etmemizi sağlar:
Web
import { collection, query, orderBy, startAt, endAt, getDocs } from 'firebase/firestore'; // Find cities within 50km of London const center = [51.5074, 0.1278]; const radiusInM = 50 * 1000; // Each item in 'bounds' represents a startAt/endAt pair. We have to issue // a separate query for each pair. There can be up to 9 pairs of bounds // depending on overlap, but in most cases there are 4. const bounds = geofire.geohashQueryBounds(center, radiusInM); const promises = []; for (const b of bounds) { const q = query( collection(db, 'cities'), orderBy('geohash'), startAt(b[0]), endAt(b[1])); promises.push(getDocs(q)); } // Collect all the query results together into a single list const snapshots = await Promise.all(promises); const matchingDocs = []; for (const snap of snapshots) { for (const doc of snap.docs) { const lat = doc.get('lat'); const lng = doc.get('lng'); // We have to filter out a few false positives due to GeoHash // accuracy, but most will match const distanceInKm = geofire.distanceBetween([lat, lng], center); const distanceInM = distanceInKm * 1000; if (distanceInM <= radiusInM) { matchingDocs.push(doc); } } }
Web
// Find cities within 50km of London const center = [51.5074, 0.1278]; const radiusInM = 50 * 1000; // Each item in 'bounds' represents a startAt/endAt pair. We have to issue // a separate query for each pair. There can be up to 9 pairs of bounds // depending on overlap, but in most cases there are 4. const bounds = geofire.geohashQueryBounds(center, radiusInM); const promises = []; for (const b of bounds) { const q = db.collection('cities') .orderBy('geohash') .startAt(b[0]) .endAt(b[1]); promises.push(q.get()); } // Collect all the query results together into a single list Promise.all(promises).then((snapshots) => { const matchingDocs = []; for (const snap of snapshots) { for (const doc of snap.docs) { const lat = doc.get('lat'); const lng = doc.get('lng'); // We have to filter out a few false positives due to GeoHash // accuracy, but most will match const distanceInKm = geofire.distanceBetween([lat, lng], center); const distanceInM = distanceInKm * 1000; if (distanceInM <= radiusInM) { matchingDocs.push(doc); } } } return matchingDocs; }).then((matchingDocs) => { // Process the matching documents // ... });
Swift
// Find cities within 50km of London let center = CLLocationCoordinate2D(latitude: 51.5074, longitude: 0.1278) let radiusInM: Double = 50 * 1000 // Each item in 'bounds' represents a startAt/endAt pair. We have to issue // a separate query for each pair. There can be up to 9 pairs of bounds // depending on overlap, but in most cases there are 4. let queryBounds = GFUtils.queryBounds(forLocation: center, withRadius: radiusInM) let queries = queryBounds.map { bound -> Query in return db.collection("cities") .order(by: "geohash") .start(at: [bound.startValue]) .end(at: [bound.endValue]) } @Sendable func fetchMatchingDocs(from query: Query, center: CLLocationCoordinate2D, radiusInMeters: Double) async throws -> [QueryDocumentSnapshot] { let snapshot = try await query.getDocuments() // Collect all the query results together into a single list return snapshot.documents.filter { document in let lat = document.data()["lat"] as? Double ?? 0 let lng = document.data()["lng"] as? Double ?? 0 let coordinates = CLLocation(latitude: lat, longitude: lng) let centerPoint = CLLocation(latitude: center.latitude, longitude: center.longitude) // We have to filter out a few false positives due to GeoHash accuracy, but // most will match let distance = GFUtils.distance(from: centerPoint, to: coordinates) return distance <= radiusInM } } // After all callbacks have executed, matchingDocs contains the result. Note that this code // executes all queries serially, which may not be optimal for performance. do { let matchingDocs = try await withThrowingTaskGroup(of: [QueryDocumentSnapshot].self) { group -> [QueryDocumentSnapshot] in for query in queries { group.addTask { try await fetchMatchingDocs(from: query, center: center, radiusInMeters: radiusInM) } } var matchingDocs = [QueryDocumentSnapshot]() for try await documents in group { matchingDocs.append(contentsOf: documents) } return matchingDocs } print("Docs matching geoquery: \(matchingDocs)") } catch { print("Unable to fetch snapshot data. \(error)") }
Kotlin
// Find cities within 50km of London val center = GeoLocation(51.5074, 0.1278) val radiusInM = 50.0 * 1000.0 // Each item in 'bounds' represents a startAt/endAt pair. We have to issue // a separate query for each pair. There can be up to 9 pairs of bounds // depending on overlap, but in most cases there are 4. val bounds = GeoFireUtils.getGeoHashQueryBounds(center, radiusInM) val tasks: MutableList<Task<QuerySnapshot>> = ArrayList() for (b in bounds) { val q = db.collection("cities") .orderBy("geohash") .startAt(b.startHash) .endAt(b.endHash) tasks.add(q.get()) } // Collect all the query results together into a single list Tasks.whenAllComplete(tasks) .addOnCompleteListener { val matchingDocs: MutableList<DocumentSnapshot> = ArrayList() for (task in tasks) { val snap = task.result for (doc in snap!!.documents) { val lat = doc.getDouble("lat")!! val lng = doc.getDouble("lng")!! // We have to filter out a few false positives due to GeoHash // accuracy, but most will match val docLocation = GeoLocation(lat, lng) val distanceInM = GeoFireUtils.getDistanceBetween(docLocation, center) if (distanceInM <= radiusInM) { matchingDocs.add(doc) } } } // matchingDocs contains the results // ... }
Java
// Find cities within 50km of London final GeoLocation center = new GeoLocation(51.5074, 0.1278); final double radiusInM = 50 * 1000; // Each item in 'bounds' represents a startAt/endAt pair. We have to issue // a separate query for each pair. There can be up to 9 pairs of bounds // depending on overlap, but in most cases there are 4. List<GeoQueryBounds> bounds = GeoFireUtils.getGeoHashQueryBounds(center, radiusInM); final List<Task<QuerySnapshot>> tasks = new ArrayList<>(); for (GeoQueryBounds b : bounds) { Query q = db.collection("cities") .orderBy("geohash") .startAt(b.startHash) .endAt(b.endHash); tasks.add(q.get()); } // Collect all the query results together into a single list Tasks.whenAllComplete(tasks) .addOnCompleteListener(new OnCompleteListener<List<Task<?>>>() { @Override public void onComplete(@NonNull Task<List<Task<?>>> t) { List<DocumentSnapshot> matchingDocs = new ArrayList<>(); for (Task<QuerySnapshot> task : tasks) { QuerySnapshot snap = task.getResult(); for (DocumentSnapshot doc : snap.getDocuments()) { double lat = doc.getDouble("lat"); double lng = doc.getDouble("lng"); // We have to filter out a few false positives due to GeoHash // accuracy, but most will match GeoLocation docLocation = new GeoLocation(lat, lng); double distanceInM = GeoFireUtils.getDistanceBetween(docLocation, center); if (distanceInM <= radiusInM) { matchingDocs.add(doc); } } } // matchingDocs contains the results // ... } });
Sınırlamalar
Konumları sorgulamak için coğrafi karma oluşturma işlemlerini kullanmak bize yeni özellikler sunar ancak kendi sınırlamalarına sahiptir:
- Yanlış pozitifler: Geohash ile sorgu yapmak tam olarak doğru değildir ve istemci tarafında yanlış pozitif sonuçları filtrelemeniz gerekir. Bu ek okumalar, uygulamanıza maliyet ve gecikme ekler.
- Uç Durumlar: Bu sorgu yöntemi, boylam/enlem çizgileri arasındaki mesafenin tahmin edilmesine dayanır. Noktalar Kuzey veya Güney Kutbu'na yaklaştıkça bu tahminin doğruluğu azalır. Bu da, coğrafi karma oluşturma sorgularının aşırı enlemlerde daha fazla yanlış pozitif içerdiği anlamına gelir.