MySQL中基于圆的搜索的ST_缓冲区等价物?

据我所知,缓冲区函数是 not yet implemented

这些功能是 不 在MySQL中。他们可能

* Buffer(g,d)

  Returns a geometry that represents all points whose distance from the geometry value g is less than or equal to a distance of d.

Euclidean distance :

select * 
from gistable g 
where SQRT(POW(circleCenterPT.x - point.x,2) + POW(circleCenterPT.y - point.y,2)) < radius

编辑:

至于MySQL中的空间函数,最新的快照似乎包含了缓冲区或距离等新函数。 您可能想尝试一下:

• http://forge.mysql.com/wiki/GIS_Functions
• http://labs.mysql.com/index.php

即使使用PostGIS,也不需要使用 ST_Buffer 功能,但是 ST_Expand 执行与此等效的操作(伪代码):

-- expand bounding box with 'units' in each direction
envelope.xmin -= units;
envelope.ymin -= units;
envelope.xmax += units;
envelope.ymax += units;
-- also Z coordinate can be expanded this way

SELECT AsText(geom) FROM mypoints
WHERE
  -- operator && triggers use of spatial index, for better performance
  geom && ST_Expand(ST_GeometryFromText('POINT(10 20)', 1234), 5) 
AND
  -- and here is the actual filter condition
  Distance(geom, ST_GeometryFromText('POINT(10 20)', 1234)) < 5

发现 Buffer vs Expand postgis用户邮件列表中的说明。

ST_Expand 功能。

下面是如何模仿 功能:

CONCAT('POLYGON((',
    X(GeomFromText('POINT(10 20)')) - 5, ' ', Y(GeomFromText('POINT(10 20)')) - 5, ',',
    X(GeomFromText('POINT(10 20)')) + 5, ' ', Y(GeomFromText('POINT(10 20)')) - 5, ',',
    X(GeomFromText('POINT(10 20)')) + 5, ' ', Y(GeomFromText('POINT(10 20)')) + 5, ',',
    X(GeomFromText('POINT(10 20)')) - 5, ' ', Y(GeomFromText('POINT(10 20)')) + 5, ',',
    X(GeomFromText('POINT(10 20)')) - 5, ' ', Y(GeomFromText('POINT(10 20)')) - 5, '))'
);

然后将此结果与如下查询组合:

SELECT AsText(geom) FROM mypoints
WHERE
  -- AFAIK, this should trigger use of spatial index in MySQL
  -- replace XXX with the of expanded point as result of CONCAT above
  Intersects(geom, GeomFromText( XXX ) )
AND 
  -- test condition
  Distance(geom, GeomFromText('POINT(10 20)')) < 5

amercader 使用基于SQRT的计算。

ST_Distance_sphere(g1, g2[, radius])

返回球体上两点和/或多点之间的最小球面距离(以米为单位),如果任何几何参数为NULL或为空,则返回NULL

计算使用球形地球和可配置的半径。可选半径参数应以米为单位。如果省略,默认半径为6370986米。如果半径参数存在但不为正,则会发生ER_错误参数错误

SELECT *
FROM gistable g
WHERE ST_Distance_Sphere(g.point, circleCenterPT) <= radius