I noticed that some error is introduced when converting from WKB to WKT
(and back). For example, the following computation of a polygon's area,
divided by itself, should return one:
SELECT (ST_Area(ST_GeomFromEWKB(ST_AsEWKB(tiger.the_geom)))
/ ST_Area(tiger.the_geom))
AS area_ratio
FROM tiger
area_ratio
-------------------
1
1
1
.
.
But when I convert to WKT as an intermediate format, the results get
thrown off by as much as 0.1% (I realize the first couple of rows don't
show this, but my tests break when the error passes that threshold):
SELECT (ST_Area(ST_GeomFromEWKT(ST_AsEWKT(tiger.the_geom)))
/ ST_Area(tiger.the_geom))
AS area_ratio
FROM tiger;
area_ratio
-------------------
1
1.00000014105231
1.00000017733961
1.00000021839733
1.00000004515224
etc.
Is this just a floating point limitation, or something else entirely?
_______________________________________________
postgis-users mailing list
[email protected]
http://postgis.refractions.net/mailman/listinfo/postgis-users
