mongodb提供地理位置运算功能，比较常用的场景比如，先判断用户所在的街道，然后看看街道附近有啥餐厅，然后算算用户与餐厅的距离什么的，官网里提供了比较详细的demo介绍不同api的用法
此处记录下dotnet core中的用法
首先安装官网提供的nuget安装包：MongoDB.Driver
定义一个点，线或者多边形进而使用驱动时通常有两种方式，以直线为例：
A.轻松些的方式，可以先获取GeoJsonLineString<GeoJson2DCoordinates>的实例，比较方便，获取实例的方式有两种
1.使用SDK中提供的方法，比如： GeoJson.Point(GeoJson.Position(100.0, 0.0))
2.通过拼接字符串进行反序列化，比如（此处注意“type”属性与里边的值都是指定的而且区分大小写，“coordinates”属性也必须是小写的）：
string lineString = "{ \"type\" : \"LineString\", \"coordinates\" : [[101.0, 0.0], [102.0, 1.0]] }";
GeoJsonLineString<GeoJson2DCoordinates> line = BsonSerializer
.Deserialize<GeoJsonLineString<GeoJson2DCoordinates>>(lineString);
B.BsonDocument的方式通常在插入的时候需要得到一个BsonDocument实例，但感觉比较累，不是很喜欢，BsonDocument实例可以通过初始化获得，也可以通过BsonDocument.Parse("")一个json字符串获得,不过位置坐标复杂的情况下比较纠结。
下面以一个判断一个人的坐标在哪个区域为例
先定义一个区域类：
public class AreaPolygon
{
public int AreaId { set; get; }
public string AreaName { set; get; }
public GeoJsonPolygon<GeoJson2DCoordinates> Geometry { set; get; }
}
然后先插入一条测试数据：
AreaPolygon pp = new AreaPolygon();
pp.AreaName = "Central Harlem North-Polo Grounds";
pp.AreaId = ;
pp.Geometry = BsonSerializer.Deserialize<GeoJsonPolygon<GeoJson2DCoordinates>>(GetPolgon());
var client = new MongoClient("mongodb://localhost:27017");
var database = client.GetDatabase("areadb");
IMongoCollection<AreaPolygon> collection = database.GetCollection<AreaPolygon>("area");
collection.InsertOne(pp);
GetPolgon()方法为一个拼接的多边形:
private string GetPolgon()
{
var json =
"{ 'type' : 'Polygon', 'coordinates' :[[[-73.93383000695911,40.81949109558767],[-73.93411701695138,40.81955053491088],[-73.93431276819767,40.81962986684897],[-73.93440040009484,40.819667782434465],[-73.93439036753757,40.81958743539698],[-73.93438112852347,40.81932807562949],[-73.9342948780807,40.81890498677685],[-73.93423576072603,40.818649319251364],[-73.93408482013453,40.81793086150489],[-73.9340746397773,40.81782651394852],[-73.93412816761214,40.8177339625139],[-73.93423519549512,40.81755488121525],[-73.93445400138874,40.81718852906137],[-73.93463790272767,40.81690804797262],[-73.93487343834981,40.8165278475176],[-73.93575548210782,40.81532558429708],[-73.93613554330996,40.8147881266393],[-73.93620957748075,40.81467385042275],[-73.93668854882762,40.81404163072326],[-73.93708163694987,40.81350614105259],[-73.93714398424214,40.81342104144455],[-73.93761714951756,40.81274036483138],[-73.93813552407511,40.812065619232335],[-73.93820642688317,40.81196760479798],[-73.93830925043022,40.81182546401121],[-73.93838748529838,40.81171844357887],[-73.93863753326706,40.81137638806709],[-73.93874394437573,40.811230820566436],[-73.93901753314599,40.810856556874455],[-73.93740733660461,40.810175611401206],[-73.93580780201182,40.80949763825762],[-73.93586263420018,40.80943020292132],[-73.93625936035667,40.808855608725686],[-73.93671827467928,40.80822047872675],[-73.93718011799034,40.80759900035796],[-73.93763439424364,40.806974606921834],[-73.93808666916728,40.80635301191095],[-73.93854407929403,40.805729652932854],[-73.93869430486176,40.80579102921082],[-73.94015793743944,40.80640908964353],[-73.94177140170032,40.807089000349656],[-73.94491601785558,40.80841350378125],[-73.94499360671229,40.80844618384186],[-73.94506102986607,40.8084745003499],[-73.94773985453432,40.80959972161701],[-73.94783892229975,40.8096411278052],[-73.9479230680906,40.809676922465236],[-73.95067975515929,40.81084296435352],[-73.95210125149222,40.81144285350124],[-73.95150537264615,40.81200768463676],[-73.95098203327805,40.81252162978943],[-73.95092865672767,40.81257507153118],[-73.95035019142966,40.81315938878694],[-73.94986218985588,40.81379998043675],[-73.94962668076091,40.81410004983843],[-73.94962653685337,40.81410023874317],[-73.94962639580584,40.81410043619291],[-73.94940550546026,40.814407409502984],[-73.9491996001398,40.81472085408311],[-73.94900927796705,40.815039942538704],[-73.9488349125204,40.81536398055535],[-73.94867681741437,40.81569228551455],[-73.94835601519225,40.816374305618886],[-73.94800732867309,40.8171165088993],[-73.94766641252582,40.817855509489],[-73.94734953979686,40.81853499822355],[-73.94703623206819,40.81920837200807],[-73.94671832033764,40.81989426803384],[-73.9464028984772,40.82057204218477],[-73.94607828674226,40.82126321606192],[-73.94516004895775,40.82087904397888],[-73.94460364603806,40.82146198118819],[-73.9440498636813,40.822051592105],[-73.94350594463333,40.82262775327937],[-73.94292366912582,40.82326058725043],[-73.9424295395631,40.823909156935464],[-73.94195569728996,40.82455444012053],[-73.9415031265368,40.82517136689069],[-73.94104840809351,40.8257926296038],[-73.94059472654726,40.82641360402922],[-73.94013953822807,40.82703869055559],[-73.9396895279914,40.827656574227866],[-73.93924885616293,40.828296351211876],[-73.93896034889055,40.82898632996019],[-73.93864026693868,40.82973887442052],[-73.93899743437669,40.82988885286428],[-73.93943428772432,40.83007611669215],[-73.93962569930143,40.83015583738796],[-73.94017089788652,40.83038439112869],[-73.94007905795213,40.83046395774134],[-73.93998939894344,40.83073096688919],[-73.93996368656906,40.83082053430401],[-73.93996366268432,40.83082060632692],[-73.9399239511922,40.83090806016343],[-73.93992389241943,40.830908177064586],[-73.93992383233875,40.8309082768776],[-73.93987063346383,40.83099179606697],[-73.93987057339177,40.83099188616358],[-73.93987049016128,40.83099197658315],[-73.9398049898395,40.831069790159276],[-73.93980484742822,40.831069960289355],[-73.93980468099204,40.83107011331944],[-73.93972831443872,40.831140898571746],[-73.9396098257029,40.83125089467677],[-73.93960970782902,40.831251002332976],[-73.93960960075394,40.83125111920869],[-73.93950338652492,40.831369460472445],[-73.9394108340693,40.83149499458965],[-73.93941078701702,40.83149507581406],[-73.93933313154191,40.83162629993882],[-73.93927119324165,40.8317616573971],[-73.93927116936439,40.8317617200385],[-73.93927114613948,40.8317617928992],[-73.93922536460632,40.83189966097508],[-73.93913480796968,40.83209759542905],[-73.93902897268019,40.83229149797039],[-73.93894859789032,40.832417335825774],[-73.9389083447814,40.8324803571376],[-73.93877360195538,40.83266321215949],[-73.93868316230177,40.83280078941747],[-73.93862894892672,40.83285794170846],[-73.93857474693523,40.83291508577085],[-73.93838508900461,40.83311350252125],[-73.93795718243024,40.83345441842215],[-73.93729719818138,40.83397732122566],[-73.93729666512158,40.833977744101354],[-73.93705905884407,40.834165988650966],[-73.93700641578684,40.83419311017997],[-73.93649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}";
var expected = json.Replace("'", "\"");
return expected;
}
然后测试下结果：
var point = GeoJson.Point(GeoJson.Position(-73.93414657, 40.82302903));
FilterDefinition<AreaPolygon> find = Builders<AreaPolygon>.Filter.GeoIntersects("Geometry", point);
var pro = Builders<AreaPolygon>.Projection.Include("AreaName");//获取结果只包含的字段
var client = new MongoClient("mongodb://localhost:27017");
var database = client.GetDatabase("areadb");
IMongoCollection<AreaPolygon> collection = database.GetCollection<AreaPolygon>("area");
var result= collection.Find(find).Project(pro).FirstOrDefault();
用BsonDocument的方式与此类型，不过对于C#这种静态类型语言，还是直接使用类型泛型比较方便（主要还是辛辛苦苦整理了一份仓储类，然后发现还用用BsonDocument怎么能忍。。。）
BsonDocument bd = new BsonDocument
{
{"AreaName", "Central Harlem North-Polo Grounds"},
{"AreaId", },
{"Geometry",new BsonDocument()
{
{ "type", "Polygon"},
{"coordinates",new BsonArray(){ 73.9557413, 40.7720266 } }
} }
};
var client = new MongoClient("mongodb://localhost:27017");
var database = client.GetDatabase("areadb");
var collection = database.GetCollection<BsonDocument>("area");
collection.InsertOne(bd); var point = GeoJson.Point(GeoJson.Position(-73.93414657, 40.82302903));
FilterDefinition<BsonDocument> find = Builders<BsonDocument>.Filter.GeoIntersects("Geometry", point);
var res = collection.Find(find);
此处coordinates太复杂了是个fload[][][]类型。。。我吓怕了，测试的时候是序列化对象成Json然后在 BsonDocument.Parse(“”)的方式获取的BsonDocument对象，有兴趣可以试试。。;