c# - 如何使用 Net Topology Suite 在 Entity Framework Core 中缓冲一个点(地理)1 米

Question

我正在将 Entity Framework Core (3.1.0) 与 Net Topology Suite 包一起使用 recommended here ，并且我很难缓冲一个点以在其周围创建圆形多边形。如果我将值 1 传递给 Buffer()，我相信这意味着 1 米，那么我最终会得到一个半径接近于的圆120 英里。

我应该用什么值来表示 1 米？我使用 SRID 为 4326 的 GeometryFactory 来创建点和多边形。我正在使用的代码大致如下:

GeometryFactory Geography = NtsGeometryServices.Instance.CreateGeometryFactory(4326);

var point = Geography.CreatePoint(coordinate.Latitude, coordinate.Longitude);
var polygonCoordinates = point.Buffer(1).Normalized().Reverse().Coordinates;
var polygon = Geography.CreatePolygon(polygonCoordinates);

Answer 1

发布问题后，我决定再次阅读 EF Core 的 Spatial 文档。正如 @Michael Entin 在评论中提到的，文档指出客户端 NTS 在执行计算时会忽略 SRID。您的输入必须投影到不同的坐标系中，进行计算并投影回来。就我而言，我必须从 4326 转到 2855。

NOTE: 2855 is the US transformation in meters, for feet use 2926. For spatial references look here, and for their visualizations look here.

我查看了示例代码，并决定将其复制到 LINQPad 中，以便我可以更详细地浏览它。正如当前存在的那样，示例代码“有效”但仅适用于具有单个坐标的几何图形。如果您传入具有多个坐标的多边形几何图形(例如我正在使用的缓冲区多边形)，那么它只会转换第一个坐标并忽略其余坐标。您必须循环遍历剩余的坐标，从中创建点，变换点，并从中获取坐标。

经过更多的尝试和错误，我更新了示例代码，以便它可以处理单坐标和多坐标几何图形。在 Google map 上检查转换后的坐标似乎可以验证其是否正确。

这是为其他遇到此问题的人提供的更新的投影代码:

public static class CoordinateExtensions {
    public static Coordinate ProjectTo(
        this Coordinate coordinate,
        int fromSrid,
        int toSrid) {
        var point = new Point(coordinate) {
            SRID = fromSrid
        };

        return point.ProjectTo(toSrid).Coordinate;
    }
}

public static class GeometryExtensions {
    private static readonly CoordinateSystemServices Services = new CoordinateSystemServices(new Dictionary<int, string> {
        { 4326, GeographicCoordinateSystem.WGS84.WKT },
        { 2855, @"
            PROJCS[""NAD83(HARN) / Washington North"",
                GEOGCS[""NAD83(HARN)"",
                    DATUM[""NAD83_High_Accuracy_Reference_Network"",
                        SPHEROID[""GRS 1980"",6378137,298.257222101,
                            AUTHORITY[""EPSG"",""7019""]],
                        TOWGS84[0, 0, 0, 0, 0, 0, 0],
                        AUTHORITY[""EPSG"", ""6152""]],
                    PRIMEM[""Greenwich"", 0,
                        AUTHORITY[""EPSG"", ""8901""]],
                    UNIT[""degree"", 0.0174532925199433,
                        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""]],
                AXIS[""X"", EAST],
                AXIS[""Y"", NORTH],
                AUTHORITY[""EPSG"", ""2855""]]
        " }
    });

    public static Geometry ProjectTo(
        this Geometry geometry,
        int toSrid) {
        if (geometry.Coordinates.Length == 1) {
            return geometry.ProjectToSingle(toSrid);
        }

        return geometry.ProjectToMany(toSrid);
    }

    private static Geometry ProjectToSingle(
        this Geometry geometry,
        int toSrid) {
        var transformation = Services.CreateTransformation(geometry.SRID, toSrid);
        var transformer = new MathTransformFilter(transformation.MathTransform);
        var transformed = geometry.Copy();

        transformed.Apply(transformer);
        transformed.SRID = toSrid;

        return transformed;
    }

    private static Geometry ProjectToMany(
        this Geometry geometry,
        int toSrid) {
        var fromSrid = geometry.SRID;
        var transformed = geometry.Copy();

        for (var i = 0; i < transformed.Coordinates.Length; i++) {
            var coordinate = transformed.Coordinates[i].ProjectTo(fromSrid, toSrid);

            transformed.Coordinates[i].CoordinateValue = coordinate.CoordinateValue;
        }

        transformed.SRID = toSrid;

        return transformed;
    }
}

public sealed class MathTransformFilter :
    ICoordinateSequenceFilter {
    private readonly MathTransform Transform;

    public MathTransformFilter(
        MathTransform transform) => Transform = transform;

    public bool Done => false;
    public bool GeometryChanged => true;

    public void Filter(
        CoordinateSequence seq,
        int i) {
        var result = Transform.Transform(new[] {
            seq.GetOrdinate(i, Ordinate.X),
            seq.GetOrdinate(i, Ordinate.Y)
        });

        seq.SetOrdinate(i, Ordinate.X, result[0]);
        seq.SetOrdinate(i, Ordinate.Y, result[1]);
    }
}