MySQL中判断一个点是否落在多边形内

关于地理空间数据，经常需要处理两个空间数据的关联关系。有很多种方法可以处理，通过编写程序算法，或者是调用数据库中对应的function。在mysql数据库中，http://dev.mysql.com/doc/refman/5.1/en/functions-for-testing-spatial-relations-between-geometric-objects.html做了详细的介绍，但是它并没有真正的实现多边形(5.6版本之前)，本文以判断一个点是否落在多边形内的主题，加以简单的扩展。

首先，建立一张简单的地理数据表，

CREATE TABLE `ci_special_zone` (  
  `id` int(11) NOT NULL auto_increment,  
  `ploygongeo` text NOT NULL,  
  PRIMARY KEY  (`id`)  
) ENGINE=MyISAM DEFAULT CHARSET=utf8; 

并插入几条数据

INSERT INTO ci_special_zone (ploygongeo) VALUES('POLYGON((113.547 22.186,113.549 22.186,113.549 22.188, 113.547 22.188,113.547 22.186))');  
INSERT INTO ci_special_zone (ploygongeo) VALUES('POLYGON((112.547 21.186,112.549 212.186,112.549 21.188, 112.547 212.188,112.547 21.186))'); 

创建function,

DELIMITER //  
  
CREATE FUNCTION myWithin(p POINT, poly POLYGON) RETURNS INT(1) DETERMINISTIC  
BEGIN  
DECLARE n INT DEFAULT 0;  
DECLARE pX DECIMAL(9,6);  
DECLARE pY DECIMAL(9,6);  
DECLARE ls LINESTRING;  
DECLARE poly1 POINT;  
DECLARE poly1X DECIMAL(9,6);  
DECLARE poly1Y DECIMAL(9,6);  
DECLARE poly2 POINT;  
DECLARE poly2X DECIMAL(9,6);  
DECLARE poly2Y DECIMAL(9,6);  
DECLARE i INT DEFAULT 0;  
DECLARE result INT(1) DEFAULT 0;  
SET pX = X(p);  
SET pY = Y(p);  
SET ls = ExteriorRing(poly);  
SET poly2 = EndPoint(ls);  
SET poly2X = X(poly2);  
SET poly2Y = Y(poly2);  
SET n = NumPoints(ls);  
WHILE i<n DO  
SET poly1 = PointN(ls, (i+1));  
SET poly1X = X(poly1);  
SET poly1Y = Y(poly1);  
IF ( ( ( ( poly1X <= pX ) && ( pX < poly2X ) ) || ( ( poly2X <= pX ) && ( pX < poly1X ) ) ) && ( pY > ( poly2Y - poly1Y ) * ( pX - poly1X ) / ( poly2X - poly1X ) + poly1Y ) ) THEN  
SET result = !result;  
END IF;  
SET poly2X = poly1X;  
SET poly2Y = poly1Y;  
SET i = i + 1;  
END WHILE;  
RETURN result;  
End;  
//  
DELIMITER ; 

最后，执行如下的sql语句

SELECT substring(ploygongeo,10,length(ploygongeo)-11) from ci_special_zone  
where myWithin(PolygonFromText('Point(113.547 22.186)'),PolygonFromText(ploygongeo))>0 limit 0,1 

坐标点113.547 22.186是经纬度，若有返回值，则表示坐标点落在所在的区间。