我想知道SELECT DISTINCT
操作员在PostGIS几何图形上的精度如何。在我的系统上,以下查询给我一个5的计数,这意味着如果插入的点相差小于1e-5,则认为插入的点相等,并且我不确定这是否是PostGIS的功能,这是我安装的问题或错误。
有人知道这是否是预期的行为吗?
CREATE TEMP TABLE test (geom geometry);
INSERT INTO test
VALUES
(St_GeomFromText('POINT (0.1 0.1)')),
(St_GeomFromText('POINT (0.001 0.001)')),
(St_GeomFromText('POINT (0.0001 0.0001)')),
(St_GeomFromText('POINT (0.00001 0.00001)')),
(St_GeomFromText('POINT (0.000001 0.000001)')),
(St_GeomFromText('POINT (0.0000001 0.0000001)')),
(St_GeomFromText('POINT (0.00000001 0.00000001)')),
(St_GeomFromText('POINT (0.000000001 0.000000001)'));
SELECT COUNT(*) FROM (SELECT DISTINCT geom FROM test) AS test;
count
-------
5
(1 row)
我在用:
$ psql --version
psql (PostgreSQL) 9.3.1
和
SELECT PostGIS_full_version();
----------------------------------------------------------------------------------------------------------------------------------------------------------------------
POSTGIS="2.1.1 r12113" GEOS="3.4.2-CAPI-1.8.2 r3921" PROJ="Rel. 4.8.0, 6 March 2012" GDAL="GDAL 1.10.1, released 2013/08/26" LIBXML="2.7.3" LIBJSON="UNKNOWN" RASTER
在OSX 10.9上