在存储的 Circle 中查找位置 [英] Find a Location within a stored Circle

问题描述

我在 MongoDB 中有表示圆的数据，如下所示:

I have data in MongoDB representing a Circle as follows:

{
    "_id" : ObjectId("54c1dc6506a4344d697f7675"),
    "location" : [ 
        23.027573, 
        72.50675800000001
    ],
    "radius" : 500
}

我想用 lat & 查询long 以确定该位置是否具有存储的经纬度和半径.

I want to query with lat & long to determine whether the location is withing stored lat&long and radius.

我尝试了以下查询但无法执行:

I tried following query but unable to execute:

db.test.find({location:{ $geoWithin: { $center: [ [ -74, 40.74 ] ,
                                                         "$radius"] } }})

我们如何在 geoWithin 查询中使用存储的半径?

How can we used stored radius in geoWithin query?

推荐答案

甚至比原来更优化，您现在可以使用 $expr 在 $match 初始 $geoNear:

Even more optimal than the original, you can now use $expr within a $match stage after the initial $geoNear:

db.collection.aggregate([
    { "$geoNear": {
        "near": {
            "type": "Point",
            "coordinates": [ 23.027573, 72.50675800000001 ],
        },
        "distanceField": "distance"
    }},
    { "$match": { "$expr": { "$lte": [ "$distance", "$radius" ] } }}
])

<小时>

实际上比第一次编写时更优化一些.现在我们可以 $redact 而不是比 $project 布尔值和 $match 之后:

db.collection.aggregate([
    // Match documents "near" the queried point
    { "$geoNear": {
        "near": {
            "type": "Point",
            "coordinates": [ 23.027573, 72.50675800000001 ],
        },
        "distanceField": "distance"
    }},

    // Calculate if distance is within radius and remove if not
    { "$redact": {
        "$cond": {
            "if": { "$lte": [ "$distance", "$radius" ] },
            "then": "$$KEEP",
            "else": "$$PRUNE"
        }
    }}
])

<小时>

您已经准确地存储了信息，但是获得结果的方法与您想象的不同.

---

You've stored the information exactly how you should, but there is a different approach to getting the results than you think.

您要使用的是 $geoNear 特别是 聚合该运算符的框架形式.您可以这样做:

What you want to use is a $geoNear and specifically the aggregation framework form of that operator. Here's what you do:

db.collection.aggregate([
    // Match documents "near" the queried point
    { "$geoNear": {
        "near": {
            "type": "Point",
            "coordinates": [ 23.027573, 72.50675800000001 ],
        },
        "distanceField": "distance"
    }},

    // Calculate if distance is within radius
    { "$project": {
        "location": 1,
        "radius": 1,
        "distance": 1,
        "within": { "$lte": [ "$distance", "$radius" ] }
    }},

    // Match only documents within the radius
    { "$match": { "within": true } }
])

因此该表单允许在结果中投影"到查询点的距离，而查询也将仅返回最近的文档.

So that form allows the distance from the queried point to be "projected" in the results, whilst the query will also only return the nearest documents.

然后您使用逻辑比较来查看距离"值是否小于半径"，因此在圆内.

Then you use a logical comparison to see if the "distance" value is less than "radius", therefore within the circle.

最后，您进行匹配以仅过滤掉within"断言为真的那些结果.

Finally you match to filter out only those results where that "within" assertion was true.

您可以向 $geoNear 添加其他选项，如文档中所示.我还强烈建议您的存储也应使用 GeoJSON 格式，因为这可能与您可能用于处理获得的结果的任何其他库更兼容.

You can add other options to $geoNear as shown in the documentation. I would also strongly suggest that your storage should also use the GeoJSON format as that is likely to be more compatible to whatever other libraries you might use to work on the results obtained.

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