Gdal.Npgsql 8.1.0

The package is an Npgsql plugin that allows you to interact with spatial data provided by the PostgreSQL PostGIS extension. On the .NET side, the plugin adds support for geometry types from the GDAL(OGR) library, allowing you to read and write them directly to PostgreSQL.

GDAL is connected via the nuget package MaxRev.Gdal.Core

Usage

Add a dependency on this package, then register the plugin on an NpgsqlDataSource. PostGIS geometry and geography columns — and arrays of them — are mapped to PgGeometry.

using Npgsql;
using Npgsql.Gdal;
using OSGeo.OGR;

var dataSourceBuilder = new NpgsqlDataSourceBuilder(connectionString);

dataSourceBuilder.UseGdal();

var dataSource = dataSourceBuilder.Build();
using (var conn = await dataSource.OpenConnectionAsync())
{
    using var point = Geometry.CreateFromWkt("POINT (30 10)");

    using (var cmd = new NpgsqlCommand("INSERT INTO data (geom) VALUES (@p)", conn))
    {
        cmd.Parameters.AddWithValue("@p", PgGeometry.FromGeometry(point, srid: 4326));
        cmd.ExecuteNonQuery();
    }

    using (var cmd = new NpgsqlCommand("SELECT geom FROM data", conn))
    using (var reader = cmd.ExecuteReader())
    {
        reader.Read();
        var value = reader.GetFieldValue<PgGeometry>(0);

        Console.WriteLine(value.GeometryType);   // no OGR object is created
        Console.WriteLine(value.SRID);

        using var geometry = value.CreateGeometry();   // you own it, you dispose it
    }
}

Why PgGeometry and not Geometry

OSGeo.OGR.Geometry wraps native memory and has to be disposed. If a query result were mapped straight to it, every geometry read from the database would be created with no owner — including the ones your code never looks at. Their memory is invisible to the .NET garbage collector, so it is released late and unpredictably.

PgGeometry holds the geometry as EWKB bytes instead:

• reading a row costs a buffer copy, and no native object is created at all;
• CreateGeometry() builds the OGR object only when you ask for one, and the caller owns it;
• FromGeometry(geometry, srid) serialises immediately — the geometry you pass stays yours;
• the type is immutable, so it is safe to cache, store and pass between threads;
• the database path never touches native GDAL, so reading and writing works without GdalBase.ConfigureAll(). Only CreateGeometry() requires the native libraries.

PgGeometry also accepts standard ISO WKB in FromWkb, and preserves whatever byte order the input used.

Migration from 8.0.x

Version 8.1.0 is a breaking change.

Reading a column now looks like this:

// 8.0.x
var eg = (reader[0] as ExtGeometry)!;
DoSomething(eg.Geometry);          // never disposed

// 8.1.0
var value = reader.GetFieldValue<PgGeometry>(0);
using var geometry = value.CreateGeometry();
DoSomething(geometry);

Fixed along the way:

• M values of POINTM/LINESTRINGM geometries were written as 0;
• the SRID of a geometry was read from the database but never written back to it;
• array mappings (geometry[], geography[]) were registered but never took effect;
• rings and sub-geometries were cloned and leaked while reading collections.