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Cratis

Cratis Arc Point storage and queries

Cratis Arc stores Cratis.Geospatial.Point as GeoJSON so you can keep a location on a document and query for nearby places. Coordinates use longitude first, then latitude.

Complete MongoDB setup to register the BSON serializers, which convert model values to MongoDB’s binary document format. The examples below add a model and query fragments to that configured host.

Usage

Section titled “Usage”

Give each store a required location:

using Cratis.Geospatial;
using MongoDB.Bson;


public class Store
{
    public ObjectId Id { get; set; }
    public required string Name { get; set; }
    public required Point Location { get; set; }
}

Inside a method, construct a point with longitude and latitude. Named arguments use the constructor’s capitalized parameter names:

var point = new Point(Longitude: -122.4194, Latitude: 37.7749);

Storage format

Section titled “Storage format”

With camel-case naming configured, Arc writes the location member as:

{"location":{"type":"Point","coordinates":[-122.4194,37.7749]}}

The coordinate array is [longitude, latitude]. Validate geographic ranges before writing a point because neither the record nor the serializer enforces them.

If a location is optional, Point? only makes the .NET property nullable. Arc’s current geometry BSON serializers neither write a null value nor read explicit BSON null. Choose and test an omission policy or a null-aware member serializer before persisting optional locations. Serializer null handling explains the difference between an absent field and an explicit null.

Querying

Section titled “Querying”

To find stores within 5,000 meters of a location, supply a driver GeoJsonPoint<GeoJson2DGeographicCoordinates> as the query origin. The stored property remains a Cratis Point; the filter’s geometry argument uses the driver’s type.

The following method fragment uses an IMongoCollection<Store> named collection. Create the spatial index during setup, then use the filter when querying:

using MongoDB.Driver;
using MongoDB.Driver.GeoJsonObjectModel;


await collection.Indexes.CreateOneAsync(new CreateIndexModel<Store>(
    Builders<Store>.IndexKeys.Geo2DSphere(store => store.Location)));


var origin = new GeoJsonPoint<GeoJson2DGeographicCoordinates>(
    new GeoJson2DGeographicCoordinates(-122.4, 37.78));
var nearbyStores = await collection.Find(Builders<Store>.Filter.Near(
    store => store.Location,
    origin,
    maxDistance: 5000)).ToListAsync();

The 2dsphere index supports spherical geometry queries. With this GeoJSON query point, maxDistance is in meters. Keep index creation out of the per-query path.

For stores inside a region, replace the proximity filter with GeoWithin and a driver GeoJSON polygon. Polygon queries shows how to construct that argument and distinguishes containment from intersection. Using a driver polygon as a filter argument does not require reading stored Cratis polygons.

Check actual spatial results against your MongoDB deployment. If your documents store a path instead of a location, continue with LineString storage and queries.

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