How to store and query an array of coordinates in C# Mongodb strongly typed driver

Question

I am using the official C# MongoDb strongly typed driver version 2.5.0 to interact with MongoDB.

I have an array of longitude and latitude coordinates and I want to store them in the MongoDB.

What is the name of the class used to store an array of coordinates? So I can lately do the following query, check If a given coordinate is near any point in the array of coordinates, how to achieve this?

Here is a simple code that demonstrate the question.

        var coordinates = new List<(double latitude, double longitude)>();

        //Store coordinates array in the database

        (double latitude, double longitude) point = (-33.847927, 150.6517805);

        int maxDistance = 300;//Max Distance in meters

        //Check if any point in the coordinates array is 300 m near the given point

Edit:-

According to this question mentioned in @CodeFuller comment below:-

MongoDB geospatial index on an array (multikey + geospatial)

MongoDB doesn't support geospatial index on arrays, so consider the following classes:

class SomeDocument {

    public ObjectId Id { get; set; }

    public string Title { get; set; }

    public List<MyClass> Locations {get; set;} = new List<MyClass>();
}

class MyClass {

    public ObjectId Id { get; set; }

    public GeoJsonPoint<GeoJson2DGeographicCoordinates> Location { get; set; 

}

How to get all instances of SomeDocument that at least have one point near a given point? And sort them by the nearest one?

Answer 1

MongoDB .NET Driver provides MongoDB.Driver.GeoJsonObjectModel.GeoJson2DGeographicCoordinates class for 2D geographic coordinates.

Here is basic usage:

1. In model class define the property with GeoJsonPoint<GeoJson2DGeographicCoordinates> type:

   public class SomeDocument
   {
       public ObjectId Id { get; set; }
   
       public string Title { get; set; }
   
       public GeoJsonPoint<GeoJson2DGeographicCoordinates> Location { get; set; }
   }
   

2. Make sure you have 2dsphere (or 2d, depends on your needs) index for Location field. You could create and index via mongo client:

   db.testCollection.createIndex( { Location : "2dsphere" } );

   Or via MongoDB .NET Driver:

   var database = mongoClient.GetDatabase("testDB");
   IMongoCollection<SomeDocument> collection = database.GetCollection<SomeDocument>("testCollection");
   collection.Indexes.CreateOne(new IndexKeysDefinitionBuilder<SomeDocument>().Geo2DSphere(x => x.Location));
   

3. Inserting data:

   collection.InsertOne(new SomeDocument
   {
       Title = "Place #1",
       Location = GeoJson.Point(new GeoJson2DGeographicCoordinates(145.89, -35.83)),
   });
   
   collection.InsertOne(new SomeDocument
   {
       Title = "Place #2",
       Location = GeoJson.Point(new GeoJson2DGeographicCoordinates(154.98, -53.38)),
   });
   

   Note that in MongoDB you specify longtitude first.

4. Finding the neighbors:

   var point = GeoJson.Point(new GeoJson2DGeographicCoordinates(145.889, -35.831));
   int maxDistance = 300;
   
   IAsyncCursor<SomeDocument> cursor = collection.FindSync(new FilterDefinitionBuilder<SomeDocument>().Near(x => x.Location, point, maxDistance: maxDistance));
   //  Check whether at least one is near the point
   var hasNeighbors = cursor.Any();
   

Sample Project on GitHub