mongo-2ds索引对超过半球范围的适用性测试

2022-11-11 16:59:36

　　以下测试均基于mongo v4.0 win10

一、GeoJSON

　　GeoJSON是一种基于json的经纬度描述数据格式。在这里主要服务于2dsphere索引查询。

　　基本格式 <type:"",coordinates:[]> ，type 对应的类型有Point、LineString(老版本有写Line的)、Polygon、MultiPoint、MultiLineString、MultiPolygon。coordinates对应格式可参照【表1】。

更详细的请自行百度。

二、2dsphere索引。

　　基于地球的经纬度。举例如下

　　存在点【28，2】，则以下区域是否与该点存在交集（$geoIntersects）的情况为

表1
	type	coordinates	是否包含
1	Point	[28,2]	是
2	LineString	[[28,1],[28,3]]	是
3	LineString	[[28,3],[28,1]]	是
4	LineString	[[27,2],[29,2]]	否
5	LineString	[[29,2],[27,2]]	否
6	Polygon	[[[27,1],[27,3],[29,3],[29,1],[27,1]]]	是
7	Polygon	[[[27,3],[27,1],[29,1],[29,3],[27,3]]]	是
8	Polygon	[[[29,1],[29,3],[27,3],[27,1],[29,1]]]	是
9	Polygon	[[[29,3],[29,1],[27,1],[27,3],[29,3]]]	是

　　从LineString的四个例子中我们可以得出：getIntersects对LineString的支持性并不高，不过考虑到现实场景中的查询，都是以一个面积为参考的，所以LineString的测验只了解一个结果，不再深入研究。

　　从Polygon的四个例子中我们可以暂时得出：GeoJSON的数组是不在乎顺序的，为了验证这个观点，我们再补做方向性的测试数据。

三、geoIntersects的方向性研究

表2
	type	coordinates	是否包含
1	Polygon	[[[27,1],[29,1],[29,3],[27,3],[27,1]]]	是
2	Polygon	[[[27,3],[29,3],[29,1],[27,1],[27,3]]]	是
3	Polygon	[[[29,3],[27,3],[27,1],[29,1],[29,3]]]	是
4	Polygon	[[[29,1],[27,1],[27,3],[29,3],[29,1]]]	是
5	Polygon	[[[29,1],[-27,3],[-27,3],[29,3],[29,1]]]	是
6
7	Polygon	[[[-179,1],[27,1],[27,3],[-179,3],[-179,1]]]	是
8	Polygon	[[[0,90],[180,90],[180,-90],[0,-90],[0,90]]]	否
9	Polygon	[[[0,90],[0,-90],[180,-90],[180,90],[0,90]]]	是
10	Polygon	[[[0,-90],[0,90],[180,90],[180,-90],[0,-90]]]	否
11	Polygon	[[[0,-90],[180,-90],[180,90],[0,90],[0,-90]]]	是
12	Polygon	[[[180,-90],[0,-90],[0,90],[180,90],[180,-90]]]	否
13	Polygon	[[[180,90],[0,90],[0,-90],[180,-90],[180,90]]]	是
14	Polygon	[[[180,90],[180,-90],[0,-90],[0,90],[180,90]]]	否
16	Polygon	[[[180,-90],[180,90],[0,90],[0,-90],[180,-90]]]	是

　　根据【表2编号1-5】到验证了以上的猜想，GeoJSON数组代表的区域是： 数组中的点连接成线，将经纬度网划分成两块，取面积小的那一块作为选定区域，进行筛选判定。

　　但是如果所选范围扩大到整个半球甚至更大，GeoJSON的数组该如何选择判定区域？从【表2编号7-16】中，我们什么也不能得出来，整个查询呈现出一种混乱的状态。又进行大量的对比实验，做了各种统计分析图后，结论依旧混乱，我甚至还去文具店买了一个地球仪。。。

　　网上进行了大量查询，最后还是在官网找到了一些信息。3.0版本以后$within(表示包含)、$geoIntersects的Polygon查询支持新的参数：crs。可以指定特殊的索引范围划分方式。如EPSG:4326，判定区域时具有严格的逆时针顺序。更多更全的知识请移步 https://docs.mongodb.com/manual/reference/operator/query/geoIntersects/#geointersects-big-poly

　　但是经过测验发现，4.0版本默认了EPSG:4326，加与不加，影响不大，测验如下（$within与$geoIntersects结果一致）：

 > db.people.find({"add":{"$within":{"$geometry":{"type":"Polygon","coordinates":[[[,],[,],[,],[,],[,]]],crs:{type:"name",properties:{name:"urn:x-mongodb:crs:strictwinding:EPSG:4326"}}}}}});

 { "_id" : ObjectId("5bb4c46d0c2287bbf737427e"), "name" : "王五", "age" : , "sex" : "男", "add" : { "type" : "Point", "coordinates" : [ ,  ] } }

 > db.people.find({"add":{"$within":{"$geometry":{"type":"Polygon","coordinates":[[[,],[,],[,],[,],[,]]],crs:{type:"name",properties:{name:"urn:x-mongodb:crs:strictwinding:EPSG:4326"}}}}}});

 { "_id" : ObjectId("5bb4c46d0c2287bbf737427e"), "name" : "王五", "age" : , "sex" : "男", "add" : { "type" : "Point", "coordinates" : [ ,  ] } }

 > db.people.find({"add":{"$within":{"$geometry":{"type":"Polygon","coordinates":[[[,],[,],[,],[,],[,]]],crs:{type:"name",properties:{name:"urn:x-mongodb:crs:strictwinding:EPSG:4326"}}}}}});

 { "_id" : ObjectId("5bb4c46d0c2287bbf737427e"), "name" : "王五", "age" : , "sex" : "男", "add" : { "type" : "Point", "coordinates" : [ ,  ] } }

 > db.people.find({"add":{"$within":{"$geometry":{"type":"Polygon","coordinates":[[[,],[,],[,],[,],[,]]],crs:{type:"name",properties:{name:"urn:x-mongodb:crs:strictwinding:EPSG:4326"}}}}}});

 { "_id" : ObjectId("5bb4c46d0c2287bbf737427e"), "name" : "王五", "age" : , "sex" : "男", "add" : { "type" : "Point", "coordinates" : [ ,  ] } }

 > db.people.find({"add":{"$within":{"$geometry":{"type":"Polygon","coordinates":[[[,],[,],[,],[,],[,]]],crs:{type:"name",properties:{name:"urn:x-mongodb:crs:strictwinding:EPSG:4326"}}}}}});

　　甚至会出现这种莫名其妙的结果：

> db.people.find({"add":{"$geoIntersects":{"$geometry":{"type":"Polygon","coordinates":[[[,],[,],[,],[,],[,]]],crs:{type:"name",properties:{name:"urn:x-mongodb:crs:strictwinding:EPSG:4326"}}}}}});

{ "_id" : ObjectId("5bcafe07377b37ef8e160bc7"), "add" : { "type" : "Point", "coordinates" : [ ,  ] } }

{ "_id" : ObjectId("5bb4c46d0c2287bbf737427e"), "name" : "王五", "age" : , "sex" : "男", "add" : { "type" : "Point", "coordinates" : [ ,  ] } }

{ "_id" : ObjectId("5bb4290d0c2287bbf737427d"), "name" : "ww wu", "age" : , "add" : { "type" : "Point", "coordinates" : [ ,  ] } }

> db.people.find({"add":{"$geoIntersects":{"$geometry":{"type":"Polygon","coordinates":[[[,],[,],[,],[,],[,]]],crs:{type:"name",properties:{name:"urn:x-mongodb:crs:strictwinding:EPSG:4326"}}}}}});

{ "_id" : ObjectId("5bcafe07377b37ef8e160bc7"), "add" : { "type" : "Point", "coordinates" : [ ,  ] } }

{ "_id" : ObjectId("5bb4c46d0c2287bbf737427e"), "name" : "王五", "age" : , "sex" : "男", "add" : { "type" : "Point", "coordinates" : [ ,  ] } }

> db.people.find({"add":{"$geoIntersects":{"$geometry":{"type":"Polygon","coordinates":[[[,],[,],[,],[,],[,]]],crs:{type:"name",properties:{name:"urn:x-mongodb:crs:strictwinding:EPSG:4326"}}}}}});

{ "_id" : ObjectId("5bcafe07377b37ef8e160bc7"), "add" : { "type" : "Point", "coordinates" : [ ,  ] } }

{ "_id" : ObjectId("5bb4c46d0c2287bbf737427e"), "name" : "王五", "age" : , "sex" : "男", "add" : { "type" : "Point", "coordinates" : [ ,  ] } }

{ "_id" : ObjectId("5bb4290d0c2287bbf737427d"), "name" : "ww wu", "age" : , "add" : { "type" : "Point", "coordinates" : [ ,  ] } }

　　可以看出，mongo对于2ds索引的支持度并不高。那么我们完全按照官方文档的格式进行测试，看能不能得出一个有规律的结果。

　　官方文档的格式：

db.places.find(

   {

     loc: {

       $geoIntersects: {

          $geometry: {

             type : "Polygon",

             coordinates: [

               [

                 [ -100, 60 ], [ -100, 0 ], [ -100, -60 ], [ 100, -60 ], [ 100, 60 ], [ -100, 60 ]

               ]

             ],

             crs: {

                type: "name",

                properties: { name: "urn:x-mongodb:crs:strictwinding:EPSG:4326" }

             }

          }

       }

     }

   }

)

　　格式定义如下：

　　1、首尾相接（以前测试的数组都是满足的）

　　2、逆时针方向书写

> db.people.find({"add":{"$geoIntersects":{"$geometry":{"type":"Polygon","coordinates":[[[,],[,-],[,-],[,],[,]]],crs:{type:"name",properties:{name:"urn:x-mongodb:crs:strictwinding:EPSG:4326"}}}}}});

{ "_id" : ObjectId("5bcafe07377b37ef8e160bc7"), "add" : { "type" : "Point", "coordinates" : [ ,  ] } }

{ "_id" : ObjectId("5bcb0145377b37ef8e160bcb"), "add" : { "type" : "Point", "coordinates" : [ ,  ] } }

{ "_id" : ObjectId("5bb4c46d0c2287bbf737427e"), "name" : "王五", "age" : , "sex" : "男", "add" : { "type" : "Point", "coordinates" : [ ,  ] } }

{ "_id" : ObjectId("5bcb0158377b37ef8e160bcc"), "add" : { "type" : "Point", "coordinates" : [ , - ] } }

{ "_id" : ObjectId("5bb4290d0c2287bbf737427d"), "name" : "ww wu", "age" : , "add" : { "type" : "Point", "coordinates" : [ ,  ] } }

> db.people.find({"add":{"$geoIntersects":{"$geometry":{"type":"Polygon","coordinates":[[[,],[,],[,],[,],[,]]],crs:{type:"name",properties:{name:"urn:x-mongodb:crs:strictwinding:EPSG:4326"}}}}}});

　　讲道理，完全没有道理。

　　总结，2ds对于小范围的within(包含)，geoIntersects（相交）的支持是正常的，超过半球或者接近半球时，判定方式让人摸不着头脑。如果有懂的大神看见了。麻烦指教以下。

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