Geo Spatial Indexing with No-SQL

Mongo DB have written a great article on Geospatial Queries, this is a quick blog post summarizing that blog post, and how to quickly setup geo spatial queries in Mongo DB. Geo Spatial queries allow you to store entities that have a coordinates, like addresses etc and perform a Near query using coordinates. 

1. Add a GeoCoordinates field to your class

 public class MyPlaceWithLocationDocument
 {
     [BsonId]
     public ObjectId Id { get; set; }

     public GeoJsonPoint<GeoJson2DCoordinates>? GeoCoordinates { get; set; }

     public string? POI { get; set; }
 }

     2. Add a index to your Mongo DB cluster, ensure that GeoCoordinates is the name of your field in your class that has the Geo coordinates.

{ "GeoCoordinates ": "2dsphere" }

3. Write your search code

private readonly IMongoCollection<T> _Collection;

 public MongoDBClient(string connectionString, string DatabaseName, string collectionName)
 {
     var settings = MongoClientSettings.FromConnectionString(connectionString);

     settings.ConnectTimeout = TimeSpan.FromSeconds(2);
     settings.ServerSelectionTimeout = TimeSpan.FromSeconds(2);

     var mongoClient = new MongoClient(settings);
     var mongoDatabase = mongoClient.GetDatabase(DatabaseName);
     _Collection = mongoDatabase.GetCollection<T>(collectionName);
 }
 
public async Task<IEnumerable<T>> GeoClosest(double lon, double lat, double? maxDistanceMetres, double? minDistanceMetres, Expression<Func<T, object>> comparisonField)
 {            
     // Instantiate builder
     var builder = Builders<T>.Filter;
     // Set center point 
     var point = GeoJson.Point(GeoJson.Position(lon, lat));
     // Create geospatial query             
     var filter = builder.Near(comparisonField, point, maxDistance: maxDistanceMetres, minDistance: minDistanceMetres);
     // Execute query
     return await _Collection.Find(filter).ToListAsync(); 
 }

 public IQueryable<T> Collection()
 {
     return _Collection.AsQueryable<T>();
 }

4. When applying and using the coordinates, remember:

Longitude values are considered the x-coordinate, while latitude values are the y-coordinate.

This is 3 easy steps to setup and use Geo Spatial searching, useful if you want to show pictures that have geo tags and search them from a no-sql database.