node.js - 就mongoDb而言，GeoJSON和旧版坐标对之间有何区别？

我正在尝试使用mongoDb的$ geoNear聚合运算符通过以下方式计算用户到当前位置的距离:

'$geoNear': {
   near: currentLocation,
   distanceField: 'distance',
   spherical: true,
}

与currentLocation类似:

{ "type" : "Point", "coordinates" : [  -122.1575745,  37.4457966 ] }

我的收藏品属于以下类型(使用 Mongoose ):

users = [{
  ....
  location : {                   // GeoJSON Point or I think it is ;)
            type: {
                type: String
            },
            coordinates: []
        }
  ....
}]

我正在使用索引(还是 Mongoose 的语法):

userSchema.index({
  location: '2dsphere'
});

现在我面临的问题是，如果我使用上述提到的currentLocation(以GeoJSON的形式)进行查询，我会得到奇怪的距离(非常大的数字)，但是如果我使用currentLocation.coordinates，即使用旧式坐标对([-122.1575745 ，37.4457966])，我得到正确的结果。但是mongoDb docs for geoNear明确表示，我们可以使用GeoJSON点或旧式坐标对进行查询。

我很好奇，想知道GeoJSON点对和传统坐标对之间到底有什么区别？

例如集合:

{ "_id" : ObjectId("5277679914c6d8f00b000003"), "location" : { "type" : "Point", "coordinates" : [  106.6202887,  -6.1293536 ] } }
{ "_id" : ObjectId("5277810148219d011c000003"), "location" : { "type" : "Point", "coordinates" : [  106.6202887,  -6.1293536 ] } }
{ "_id" : ObjectId("5281c7ba2dfd7bdc64000003"), "location" : { "type" : "Point", "coordinates" : [  -86.9248483,  33.4480108 ] } }
{ "_id" : ObjectId("5281c8b82dfd7bdc64000004"), "location" : { "type" : "Point", "coordinates" : [  -74.0087126,  40.7136487 ] } }
{ "_id" : ObjectId("5281c9782dfd7bdc64000005"), "location" : { "type" : "Point", "coordinates" : [  -122.1575745,  37.4457966 ] } }

错误的结果:

[{"location":{"type":"Point","coordinates":[-122.1575745,37.4457966]},"dis":13.69288259318155},
 {"location":{"type":"Point","coordinates":[-86.9248483,33.4480108]},"dis":12697164592.388557},
 {"location":{"type":"Point","coordinates":[-74.0087126,40.7136487]},"dis":16328789117.58145},
 {"location":{"type":"Point","coordinates":[106.6202887,-6.1293536]},"dis":55446284682.14049},
 {"location":{"type":"Point","coordinates":[106.6202887,-6.1293536]},"dis":55446284682.14049}]

最佳答案

让我们创建一些示例文档和地理空间索引:

> db.foo.insert({name: "Warsaw", location: {"type" : "Point", "coordinates" : [21.016667, 52.233333]}})
> db.foo.insert({name: "Stockholm", location: {"type" : "Point", "coordinates" : [18.068611, 59.329444]}})
> db.foo.ensureIndex({"location": "2dsphere"})

华沙PL到Stockholm SE的距离大约为810公里，所以让我们检查一下它是否按预期工作。首先，我们可以获取斯德哥尔摩的文档。

> Stockholm = db.foo.findOne({name: "Stockholm"})

现在我们可以使用geoNear运行查询:

> db.runCommand({ geoNear: 'foo', near: Stockholm.location.coordinates,  spherical: true })
{
    "ns" : "test.foo",
    "results" : [
        {
            "dis" : 6.558558954334308e-10,
            "obj" : {
                "_id" : ObjectId("52876ab0b12c6fc62f5d9311"),
                "name" : "Stockholm",
                "location" : {
                    "type" : "Point",
                    "coordinates" : [
                        18.068611,
                        59.329444
                    ]
                }
            }
        },
        {
            "dis" : 0.12715355275490586,
            "obj" : {
                "_id" : ObjectId("5287697eb12c6fc62f5d9310"),
                "name" : "Warsaw",
                "location" : {
                    "type" : "Point",
                    "coordinates" : [
                        21.016667,
                        52.233333
                    ]
                }
            }
        }
    ],
    "stats" : {
        "time" : 9,
        "nscanned" : 3,
        "avgDistance" : 0.06357677670538088,
        "maxDistance" : 0.12715355275490586
    },
    "ok" : 1
}

斯德哥尔摩和斯德哥尔摩之间的距离符合预期，接近0。斯德哥尔摩到华沙的距离是0.12715355275490586。当您使用旧版坐标对运行查询时，您会获得以弧度为单位的结果，因此我们必须将此值乘以地球半径:

> 0.12715355275490586 * 6371.0
810.0952846015052

到目前为止，一切都很好。让我们检查使用geojson作为查询是否得到相似的结果。

> db.runCommand({ geoNear: 'foo', near: Stockholm.location,  spherical: true })
{
    "ns" : "test.foo",
    "results" : [
        {
            "dis" : 0.004183114486663965,
            "obj" : {
                "_id" : ObjectId("52876ab0b12c6fc62f5d9311"),
                "name" : "Stockholm",
                "location" : {
                    "type" : "Point",
                    "coordinates" : [
                        18.068611,
                        59.329444
                    ]
                }
            }
        },
        {
            "dis" : 810998.0748260651,
            "obj" : {
                "_id" : ObjectId("5287697eb12c6fc62f5d9310"),
                "name" : "Warsaw",
                "location" : {
                    "type" : "Point",
                    "coordinates" : [
                        21.016667,
                        52.233333
                    ]
                }
            }
        }
    ],
    "stats" : {
        "time" : 4,
        "nscanned" : 3,
        "avgDistance" : 405499.0395045898,
        "maxDistance" : 810998.0748260651
    },
    "ok" : 1
}

斯德哥尔摩和斯德哥尔摩之间的距离再次接近0。斯德哥尔摩到华沙的距离是810998.0748260651。使用GeoJSON运行geoNear查询时，距离以米为单位。 810998.0748260651大约等于810公里，所以这里没什么奇怪的。

> 810998.0748260651 / 1000
810.9980748260651

两种解决方案之间的差异可能较小，但这只是FP算法。

> Math.abs(810.0952846015052 - 810.9980748260651)
0.902790224559908

当您将find命令与$near运算符一起使用时。在传统坐标对上创建简单的2d索引时，可以同时使用{$near: Stockholm.location.coordinates}和{$near: {$geometry: Stockholm.location}对其进行查询。如果您有2dsperhical，则仅{$near: {$geometry: Stockholm.location}将起作用。