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I have a couple of featureclasses in a 10.2 geodatabase/PostgreSQL 9.2.2 database and I've been struggling with the FeatureCompare tool--it is telling me geometries are different on some features where I know them to be at least spatially equal.

Luckily, I have an ID and I could join between the 2 tables in PGAdmin and compare geometry. The ~= opreator and the ST_Equals both return true for every row. Then I modified 1 feature by moving 1 vertex 800 ft to the South.

When I run my query, ST_Equals returns false which is what I expect. But ~= still returns true??? Why is that?

select t1.shape,t2.shape ,(t1.shape ~= t2.shape) as exactequal , ST_Equals(t1.shape , t2.shape) spatialequal, (t1.shape = t2.shape) bndequal
from  pg.Test1 t1
inner join pt.Bnd2 t2
on t1.polygon_id=t2.polygon_id
where t1.objectid = 6389

enter image description here

I trying to figure out if this is a bug or if I'm misunderstanding the operators.

"PostgreSQL 9.2.2, compiled by Visual C++ build 1600, 64-bit"
"POSTGIS="2.0.4" GEOS="3.4.2-CAPI-1.8.2 r0" PROJ="Rel. 4.8.0, 6 March 2012" GDAL="GDAL 1.10.0, released 2013/04/24"

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1 Answer 1

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As the doc says ~= only compares bounding boxes. So if you move a point in a way that it doesn't change the bounding box ~= still returns true.

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  • Maybe i was looking at old docs. The one i was looking at said equal sign only was bounding box compare.
    – Jay Cummins
    Commented Feb 1, 2014 at 11:29
  • Sure enough, I was looking at 1.3 docs: The "~=" operator is the "same as" operator. It tests actual geometric equality of two features.. And 2.0 docs have it as: Returns TRUE if A's bounding box is the same as B's..
    – Jay Cummins
    Commented Feb 1, 2014 at 14:16

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