st_intersects Vs st_overlaps

Question

这两个查询的区别是什么：

select a.gid, sum(length(b.the_geom)) 
  from polygons as a 
     , roads as b 
 where st_intersects(a.the_geom,b.the_geom) 
 group by a.gid ;

select a.gid, sum(length(b.the_geom)) 
  from polygons as a 
     , roads as b 
 where st_overlaps(a.the_geom,b.the_geom) 
 group by a.gid ;

其中第一个查询给出了正确的输出，而第二个查询根本没有检索任何行。与多边形相交的道路也会与之重叠，对吧？

Answer 1

来自PostGIS的文档

http://postgis.net/docs/ST_Intersects.html

如果一个几何图形或地理图形共享任何部分的空间，则它们相交。重叠，接触，都暗示着空间的交集。如果前面提到的任何一个返回true，那么几何图形在空间上也是相交的。

http://postgis.net/docs/ST_Overlaps.html

如果几何图形“空间重叠”，则

返回TRUE。我们的意思是它们相交，但一个并不完全包含另一个。

不同之处在于:如果两个几何图形100%重叠，则它们不再重叠。

下面是一个POSTGIS示例：

SELECT ST_Overlaps(a,b) As a_overlap_b, ST_Intersects(a, b) As a_intersects_b, ST_Contains(b, a) As b_contains_a
FROM (SELECT 
    ST_Polygon(ST_GeomFromText('LINESTRING(1 1,3 1,3 3,1 1)'), 4326)  As a,
    ST_Polygon(ST_GeomFromText('LINESTRING(1 1,3 1,3 3,1 1)'), 4326)  As b)
    As foo;
    -- INTERSECT is TRUE, OVERLAP is FALSE because B equals A

    SELECT ST_Overlaps(a,b) As a_overlap_b, ST_Intersects(a, b) As a_intersects_b, ST_Contains(b, a) As b_contains_a
FROM (SELECT 
    ST_Polygon(ST_GeomFromText('LINESTRING(1 1,3 1,3 3,1 1)'), 4326)  As a,
    ST_Polygon(ST_GeomFromText('LINESTRING(1 1,4 1,4 4,1 1)'), 4326)  As b)
    As foo;
    -- INTERSECT is TRUE, OVERLAP is FALSE because B contains A

    SELECT ST_Overlaps(a,b) As a_overlap_b, ST_Intersects(a, b) As a_intersects_b, ST_Contains(b, a) As b_contains_a
FROM (SELECT 
    ST_Polygon(ST_GeomFromText('LINESTRING(0 0,2 0,2 2,0 0)'), 4326)  As a,
    ST_Polygon(ST_GeomFromText('LINESTRING(1 1,3 1,3 3,1 1)'), 4326)  As b)
    As foo;
    -- INTERSECT is TRUE, OVERLAP is TRUE because not all of A intersects B and not all of B intersects A