st_intersects Vs的st_overlaps(st_intersects Vs st_o

是什么这两个查询之间的区别：

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 ;

当第一个查询给正确的输出，而第二个查询检索没有行的。相交多边形还路重叠，对吗？

从PostGIS的的文件

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

如果几何或地理股空间任何部分，然后它们相交。重叠，倒是，在所有暗示的空间交集。如果上述任何回报的话，那么也几何空间相交。

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

如果几何“空间重叠”，则返回TRUE。我们的意思，他们相交，但是一个不完全包含另一个。

所不同的是：如果两个几何重叠的100％，它们不重叠了。

这里是一个POSTGIS例如：

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