Question

根据文档，2dSphere geospatial index也可以用于复杂的GeoJSON形状，如LineString和Polygon，它们由多个节点组成。

当您使用$nearSphere搜索填充了此类复杂形状的字段以接近另一个GeoJSON对象（可能也是一个复杂的形状）时，这些形状的距离将如何计算？

它会比较形状的最近节点吗？最遥远的节点？一些平均的节点？形状任何边缘上的最近点？

Answer 1

$nearSphere运算符只允许您指定一个点（您可以通过提供maxDistance参数来定义“球体”的中心）。因此，唯一有意义的答案可能是关于如何最接近最远的形状排序。

答案是所有具有等距“最近”点的形状将在具有最近点的形状之前进行排序。换句话说，点和形状之间的距离是点与形状上最近点之间的距离。

我们可以通过运行$nearSphere的{{3}}命令的变体来看到它返回计算出的距离然后我们可以检查。

我们的样本数据：

> db.near.find()
{ "_id" : 10, "loc" : { "type" : "Polygon", "coordinates" : [ [ [ 0, 0 ], [ 0, 5 ], [ 5, 5 ], [ 5, 0 ], [ 0, 0 ] ] ] } }
{ "_id" : 11, "loc" : { "type" : "Polygon", "coordinates" : [ [ [ 1, 1 ], [ 1, 5 ], [ 5, 5 ], [ 5, 1 ], [ 1, 1 ] ] ] } }
{ "_id" : 12, "loc" : { "type" : "Polygon", "coordinates" : [ [ [ 0, 0 ], [ 0, 6 ], [ 6, 6 ], [ 6, 0 ], [ 0, 0 ] ] ] } }
{ "_id" : 13, "loc" : { "type" : "Polygon", "coordinates" : [ [ [ 0, 0 ], [ 0, 6 ], [ 6, 6 ], [ 6, 0 ], [0, 0 ] ], [ [ 1, 1 ], [ 1, 5 ], [ 5, 5 ], [ 5, 1 ], [ 1, 1 ] ] ] } }
{ "_id" : 14, "loc" : { "type" : "Polygon", "coordinates" : [ [ [ 0, 0 ], [ 0, 6 ], [ 6, 6 ], [ 6, 0 ], [ 0, 0 ] ], [ [ 0.1, 0.1 ], [ 0.1, 5 ], [ 5, 5 ], [ 5, 0.1 ], [ 0.1, 0.1 ] ] ] } }
{ "_id" : 15, "loc" : { "type" : "Polygon", "coordinates" : [ [ [ 0, 0 ], [ 0, 1 ], [ 1, 1 ], [ 1, 0 ], [0, 0 ] ],  [ [ 0.1, 0.1 ], [ 0.1, 0.5 ], [ 0.5, 0.5 ], [ 0.5, 0.1 ], [ 0.1, 0.1 ] ] ] } }
{ "_id" : 16, "loc" : { "type" : "LineString", "coordinates" : [ [ 0, 0 ], [ 0.1, 0.1 ] ] } }
{ "_id" : 17, "loc" : { "type" : "LineString", "coordinates" : [ [ 0, 0 ], [ 0, 0.1 ] ] } }
{ "_id" : 18, "loc" : { "type" : "LineString", "coordinates" : [ [ 0, 0 ], [ 0.1, 0 ] ] } }

我们使用$ nearSphere的结果：

{ "_id" : 16, "loc" : { "type" : "LineString", "coordinates" : [  [ 0, 0 ],  [  0.1,  0.1 ] ] } }
{ "_id" : 18, "loc" : { "type" : "LineString", "coordinates" : [  [ 0, 0 ],  [  0.1,  0 ] ] } }
{ "_id" : 14, "loc" : { "type" : "Polygon", "coordinates" : [  [  [ 0, 0 ], [ 0, 6 ], [     6,  6 ],    [   6,  0 ],    [   0,  0 ] ],  [   [   0.1,    0.1 ],  [   0.1,    5 ],    [   5,  5 ],    [   5,  0.1 ],  [   0.1,    0.1 ] ] ] } }
{ "_id" : 13, "loc" : { "type" : "Polygon", "coordinates" : [  [  [ 0, 0 ], [ 0, 6 ], [     6,  6 ],    [   6,  0 ],    [   0,  0 ] ],  [   [   1,  1 ],    [   1,  5 ],    [   5,  5 ],    [   5,  1 ],    [   1,  1 ] ] ] } }
{ "_id" : 15, "loc" : { "type" : "Polygon", "coordinates" : [  [  [ 0, 0 ], [ 0, 1 ], [     1,  1 ],    [   1,  0 ],    [   0,  0 ] ],  [   [   0.1,    0.1 ],  [   0.1,    0.5 ],  [   0.5,    0.5 ],  [   0.5,    0.1 ],  [   0.1,    0.1 ] ] ] } }
{ "_id" : 12, "loc" : { "type" : "Polygon", "coordinates" : [  [  [ 0, 0 ],  [  0,  6 ],  [  6,  6 ],  [  6,  0 ],  [  0,  0 ] ] ] } }
{ "_id" : 17, "loc" : { "type" : "LineString", "coordinates" : [  [ 0, 0 ],  [  0,  0.1 ] ] } }
{ "_id" : 10, "loc" : { "type" : "Polygon", "coordinates" : [  [  [ 0, 0 ],  [  0,  5 ],  [  5,  5 ],  [  5,  0 ],  [  0,  0 ] ] ] } }
{ "_id" : 11, "loc" : { "type" : "Polygon", "coordinates" : [  [  [ 1, 1 ],  [  1,  5 ],  [  5,  5 ],  [  5,  1 ],  [  1,  1 ] ] ] } }

运行$geoNear命令，我们可以确认从点到形状的距离（省略空间考虑的坐标）：

> db.runCommand({geoNear:"near", near: {type:"Point", coordinates:[0,0]}, spherical:true})
[
    {
        "dis" : 0,
        "obj" : {
            "_id" : 16,
            "loc" : {
                "type" : "LineString"
            }
        }
    },
    {
        "dis" : 0,
        "obj" : {
            "_id" : 18,
            "loc" : {
                "type" : "LineString"
            }
        }
    },
    {
        "dis" : 0,
        "obj" : {
            "_id" : 14,
            "loc" : {
                "type" : "Polygon"
            }
        }
    },
    {
        "dis" : 0,
        "obj" : {
            "_id" : 13,
            "loc" : {
                "type" : "Polygon"
            }
        }
    },
    {
        "dis" : 0,
        "obj" : {
            "_id" : 15,
            "loc" : {
                "type" : "Polygon"
            }
        }
    },
    {
        "dis" : 0,
        "obj" : {
            "_id" : 12,
            "loc" : {
                "type" : "Polygon"
            }
        }
    },
    {
        "dis" : 0,
        "obj" : {
            "_id" : 17,
            "loc" : {
                "type" : "LineString"
            }
        }
    },
    {
        "dis" : 0,
        "obj" : {
            "_id" : 10,
            "loc" : {
                "type" : "Polygon"
            }
        }
    },
    {
        "dis" : 157424.6238723255,
        "obj" : {
            "_id" : 11,
            "loc" : {
                "type" : "Polygon"
            }
        }
    }
]

正如您所看到的，即使形状的大小和形状各不相同，每个形状（从[1,1]开始的最后一个形状除外）到点[0,0]的距离为0。在与指定点具有相同距离的文档中，未定义订单。这意味着，即使看起来确定性，也不能保证是相同的。

地理空间$ nearSphere运算符如何与LineString和Polygon交互

1 个答案: