通过 EF Core 和 NetTopologySuite 使用半径按区域搜索

Question

我正在构建一个应用程序，我需要它能够根据他们的“送货区域”搜索企业

例如，London Business 提供距离纬度/经度最远 10000 米的服务 Southampton Business 提供距离纬度/经度 1000 米的服务

我是其中的一部分，使用 EF Core 和 NetTopologySuite。

我正在使用以下简化代码：

var geometryFactory = NtsGeometryServices.Instance.CreateGeometryFactory(srid: 4326);

var londonBusiness = new Business
{
    Name = "London Business",
    Area = geometryFactory.CreatePoint(new Coordinate(-0.127758, 51.507351)),
    AreaRadius = 10000
};

var southamptonBusiness = new Business
{
    Name = "Southampton Business",
    Area = geometryFactory.CreatePoint(new Coordinate(1.4044, 50.9097)),
    AreaRadius = 1000
};

await _dbContext.Businesses.AddAsync(londonBusiness);
await _dbContext.Businesses.AddAsync(southamptonBusiness);
await _dbContext.SaveChangesAsync();


// QUERY

// this is very clsoe to the londonBusiness (a couple of km)
var searchLocation = _geometryFactory.CreatePoint(new Coordinate(-0.142500, 51.539188));

var query = _dbContext
    .Businesses
    .Where(x => x.AreaLocation.Distance(searchLocation) <= x.AreaRadius)
    .ToList()

    // this projection is for debug purposes
    .Select(x => new
    {
        Distance = x.AreaLocation.Distance(searchLocation),
        radius = x.AreaRadius
    });

这将返回以下结果：

{ Name = "London Business", Distance = 0.035084485645370242, Radius = 10000 }
{ Name = "Southampton Business", Distance = 1.6700762713552944, Radius = 1000 }

所以，我认为我的问题在于距离 我显然误解了距离是/相关的。 他们是相对正确的 - 伦敦商务距离远小于南安普敦商务

有没有按米查询的方法？

Answer 1

参考：SRID Ignored during client operations：

NTS 在操作期间忽略 SRID 值。它假设一个平面坐标系。这意味着，如果您根据经度和纬度指定坐标，一些客户评估的值（例如距离、长度和面积）将以度为单位，而不是米。对于更有意义的值，您首先需要使用 ProjNet4GeoAPI 等库将坐标投影到另一个坐标系，然后再计算这些值。

这是因为 NetTopologySuite 是 JTS 拓扑套件的 .NET 端口。参考：NetTopologySuite：

一种 .NET GIS 解决方案，对于 .NET 平台来说是快速且可靠的。 NetTopologySuite 是 JTS 拓扑套件提供的所有功能的直接端口：NTS 以“.NET 方式”公开 JTS，例如使用属性、索引器等...

JTS 网站的摘录也解释了 NTS 的功能：“JTS 拓扑套件是用于建模和操作二维线性几何的 API。它提供了许多几何谓词和函数。JTS 符合 SQL 的简单特征规范由开放 GIS 联盟发布。”

Answer 2

演示使用ProjNet4GeoAPI 包将过滤值的点映射到投影坐标系，并使用它们计算距离（以米为单位）。

using GeoAPI.CoordinateSystems.Transformations;
using Microsoft.EntityFrameworkCore;
using NetTopologySuite.Geometries;
using ProjNet.CoordinateSystems;
using ProjNet.CoordinateSystems.Transformations;
using System.Diagnostics;
using System.Linq;

namespace ConsoleApp7
{
    public class Location
    {
        public int Id { get; set; }
        public Point Point { get; set; }
    }
    public class Business
    {
        public int Id { get; set; }
        public Point Point { get; set; }
        public double Distance { get; set; }
    }
    public class MyDbContext : DbContext
    {
        public DbSet<Location> Locations { get; set; }
        public DbSet<Business> Businesses { get; set; }
        protected override void OnConfiguring(DbContextOptionsBuilder optionsBuilder)
        {
            optionsBuilder.UseSqlServer("Server=DESKTOP-5PVJ0I5;Database=geog;Integrated Security=true;", 
                options => options.UseNetTopologySuite());

            base.OnConfiguring(optionsBuilder);
        }
    }
    class Program
    {
        static void Main(string[] args)
        {
            CoordinateTransformationFactory ctfac = new CoordinateTransformationFactory();

            var from = GeographicCoordinateSystem.WGS84;
            var to = ProjectedCoordinateSystem.WGS84_UTM(30, true);

            // convert points from one coordinate system to another
            ICoordinateTransformation trans = ctfac.CreateFromCoordinateSystems(from, to);

            var businessCoordinate = new GeoAPI.Geometries.Coordinate(-0.127758, 51.507351);
            var searchLocationCoordinate = new GeoAPI.Geometries.Coordinate(-0.142500, 51.539188);

            var mathTransform = trans.MathTransform;
            var businessLocation = mathTransform.Transform(businessCoordinate);
            var searchLocation = mathTransform.Transform(searchLocationCoordinate);

            // calculate distance in meters
            var dist = businessLocation.Distance(searchLocation); // 3687m


            // arrange db
            var dbContext = new MyDbContext();
            dbContext.Database.Migrate();

            var location = new Location()
            {
                Point = new Point(searchLocationCoordinate.X, searchLocationCoordinate.Y) {  SRID = 4326, }
            };

            // one business has radius to include location point
            var businessWithLocationInRadius = new Business()
            {
                Distance = 4000,
                Point = new Point(businessCoordinate.X, businessCoordinate.Y) { SRID = 4326, }
            };

            // and this one has too low range
            var businessWithLocationNOTInRadius = new Business()
            {
                Distance = 3500,
                Point = new Point(businessCoordinate.X, businessCoordinate.Y) { SRID = 4326, }
            };

            dbContext.Add(location);
            dbContext.Add(businessWithLocationInRadius);
            dbContext.Add(businessWithLocationNOTInRadius);

            dbContext.SaveChanges();

            var query = dbContext
                .Businesses
                .Where(x => x.Point.Distance(location.Point) <= x.Distance)
                .ToList()

                .Select(x => new
                {
                    Distance = searchLocation
                        .Distance(mathTransform.Transform(new GeoAPI.Geometries.Coordinate(x.Point.X, x.Point.Y))), // 3687m
                    Radius = x.Distance
                })
                
                .ToList();

            Debugger.Break();
        }
    }
}