Question

我正在使用kartoza码头工人图像来运行带有Postgis的Postgres服务器。我有一个使用ASP.NET Core应用程序和Enity Framework Core消耗的数据库。该数据库包含一个名为Park的表，该表由以下实体表示：

[Table("Park")]
public class Park
{
     [Key]
     public int Id { get; set; }

     [Column(TypeName = "geography (point)")]
     public Point Location { get; set; }
}

我正在创建文档指定的DbContext：

protected override void OnModelCreating(ModelBuilder modelBuilder)
{
    modelBuilder.HasPostgresExtension("postgis");

    modelBuilder.Entity<Park>()
        .Property(p => p.Location)
        .HasColumnType("geography (point)");
}

我用以下代码为数据库播种：

if (!Parks.Any())
{
    var park = new Park
    {
        Location = new Point(48.8566, 2.3522)
        {
            SRID = 4326
        }
    };

    Parks.Add(park);
    this.SaveChanges();
}

现在要测试我的代码，我计算出该公园与某个点之间的距离：

结果对应于笛卡尔坐标系中两点之间的几何距离，而不是地理距离。是否有可能获得与以下查询等效的结果：

Answer 1

如here所述，需要坐标系统的投影才能计算地理距离。 ProjNet4GeoAPI用于使用防护方法进行投影：

static class GeometryExtensions
{
    static readonly IGeometryServices _geometryServices = NtsGeometryServices.Instance;
    static readonly ICoordinateSystemServices _coordinateSystemServices
        = new CoordinateSystemServices(
            new CoordinateSystemFactory(),
            new CoordinateTransformationFactory(),
            new Dictionary<int, string>
            {
                // Coordinate systems:

                // (3857 and 4326 included automatically)

                // This coordinate system covers the area of our data.
                // Different data requires a different coordinate system.
                [2855] =
                @"
                    PROJCS[""NAD83(HARN) / Washington North"",
                        GEOGCS[""NAD83(HARN)"",
                            DATUM[""NAD83_High_Accuracy_Regional_Network"",
                                SPHEROID[""GRS 1980"",6378137,298.257222101,
                                    AUTHORITY[""EPSG"",""7019""]],
                                AUTHORITY[""EPSG"",""6152""]],
                            PRIMEM[""Greenwich"",0,
                                AUTHORITY[""EPSG"",""8901""]],
                            UNIT[""degree"",0.01745329251994328,
                                AUTHORITY[""EPSG"",""9122""]],
                            AUTHORITY[""EPSG"",""4152""]],
                        PROJECTION[""Lambert_Conformal_Conic_2SP""],
                        PARAMETER[""standard_parallel_1"",48.73333333333333],
                        PARAMETER[""standard_parallel_2"",47.5],
                        PARAMETER[""latitude_of_origin"",47],
                        PARAMETER[""central_meridian"",-120.8333333333333],
                        PARAMETER[""false_easting"",500000],
                        PARAMETER[""false_northing"",0],
                        UNIT[""metre"",1,
                            AUTHORITY[""EPSG"",""9001""]],
                        AUTHORITY[""EPSG"",""2855""]]
                "
            });

    public static IGeometry ProjectTo(this IGeometry geometry, int srid)
    {
        var geometryFactory = _geometryServices.CreateGeometryFactory(srid);
        var transformation = _coordinateSystemServices.CreateTransformation(geometry.SRID, srid);

        return GeometryTransform.TransformGeometry(
            geometryFactory,
            geometry,
            transformation.MathTransform);
    }
}

现在结果似乎更正确：

PS：除了ProjNet4GeoAPI金块包装外，扩展方法还需要NetTopologySuite。

使用带有EF Core的NetTopologySuite和postgis计算两点之间的地理距离

1 个答案: