【NetTopologySuite类库】geojson和shp互转，和自定义对象互转

geojson介绍

1. 示例

在visual studio中使用NuGet中安装了三个库（.net4.7.2环境）：

• NetTopologySuite 2.5
• NetTopologySuite.IO.Esri.Shapefile 1.2
• NetTopologySuite.IO.GeoJSON 4.0

1.1 shp数据转geojson

先创建一个shp文件作为例子：

using NetTopologySuite.Geometries;
using NetTopologySuite.IO;
using NetTopologySuite.IO.Esri;
using NetTopologySuite.Features;
using System.Collections.Generic;
using System.IO;

//创建一个用于测试的shp文件
var r = new WKTReader();
var geo1 = r.Read("polygon((0 0,0 10,10 10,10 0,0 0))");
var geo2 = r.Read("polygon((10 0,10 10,20 10,20 0,10 0))");
Save("./Tmp/data.shp", geo1, geo2);
    
//工具方法
public static void Save(string shpPath, params Geometry[] geos)
{
    Directory.CreateDirectory(Path.GetDirectoryName(shpPath));
    var features = geos.Select(x => new Feature(x, null)).ToList();
    Shapefile.WriteAllFeatures(features, shpPath);
}

再读取shp，将其转为geojson：

public void TestMethod1()
{
	//读取shp文件，转geojson
    var features = Shapefile.ReadAllFeatures("./Tmp/data.shp");
    var modifiedJson = new GeoJsonWriter().Write(features);
    File.WriteAllText("./Tmp/output.geojson", modifiedJson);
}

生成的geojson：

[
  {
    "type": "Feature",
    "bbox": [0.0, 0.0, 10.0, 10.0],
    "geometry": {
      "type": "MultiPolygon",
      "coordinates": [
        [
          [
            [0.0, 0.0],
            [10.0, 0.0],
            [10.0, 10.0],
            [0.0, 10.0],
            [0.0, 0.0]
          ]
        ]
      ]
    },
    "properties": {
      "Id": 1
    }
  },
  {
    "type": "Feature",
    "bbox": [10.0, 0.0, 20.0, 10.0],
    "geometry": {
      "type": "MultiPolygon",
      "coordinates": [
        [
          [
            [10.0, 0.0],
            [20.0, 0.0],
            [20.0, 10.0],
            [10.0, 10.0],
            [10.0, 0.0]
          ]
        ]
      ]
    },
    "properties": {
      "Id": 1
    }
  }
]

1.2 geojson转shp数据

public void TestMethod2()
{
    var json = File.ReadAllText("./Tmp/output.geojson");
    var reader = new GeoJsonReader();
    var features = reader.Read<Feature[]>(json);
    Shapefile.WriteAllFeatures(features, "./Tmp/data2.shp");
}

1.2 自定义对象转geojson

自定义一个类（里面有属性，有几何Geometry ）：

 public class Item
 {
     public string Name { get; set; } = "Layer";
     public Geometry Geo { get; set; }
     public Dictionary<string, object> Attrs { get; set; }

     public Item(string name, Geometry geo, Dictionary<string, object> attrs)
     {
         Name = name;
         Geo = geo;
         Attrs = attrs;
     }
 }

为该类创建对象数组，并将其转为geojson：

public void TestMethod3()
{
    var r = new WKTReader();
    var geo1 = r.Read("polygon((0 0,0 10,10 10,10 0,0 0))");
    var geo2 = r.Read("polygon((10 0,10 10,20 10,20 0,10 0))");

    var item1 = new Item("A", geo1, new Dictionary<string, object>()
    {
        { "key", 1}, { "value", 2} 
    });
    var item2 = new Item("A", geo1, new Dictionary<string, object>()
    {
        { "key", 1}, { "value", 2}
    });
    var items = new Item[] {item1, item2 };
    var modifiedJson = new GeoJsonWriter().Write(items);
    File.WriteAllText("./Tmp/output2.geojson", modifiedJson);      
}

转成的geojson：

[
  {
    "Name": "A",
    "Geo": {
      "type": "Polygon",
      "coordinates": [
        [
          [0.0, 0.0],
          [10.0, 0.0],
          [10.0, 10.0],
          [0.0, 10.0],
          [0.0, 0.0]
        ]
      ]
    },
    "Attrs": {
      "key": 1,
      "value": 2
    }
  },
  {
    "Name": "A",
    "Geo": {
      "type": "Polygon",
      "coordinates": [
        [
          [0.0, 0.0],
          [10.0, 0.0],
          [10.0, 10.0],
          [0.0, 10.0],
          [0.0, 0.0]
        ]
      ]
    },
    "Attrs": {
      "key": 1,
      "value": 2
    }
  }
]

1.3 geojson转自定义对象

public void TestMethod4()
{
    var json = File.ReadAllText("./Tmp/output2.geojson");
    var reader = new GeoJsonReader();
    var obj = reader.Read<Item[]>(json);
}