SQLServer generating invalid WKT

Question

I am a GIS novice using SQL 2008, with C# and the NetTopologySuite WKTReader type to work with some geometries.

I have some data which I have been able to save into the database but when I read back out the I receive a 24144 error with suggestions to use MakeValid() to convert it to a valid instance.

I don't understand whats wrong with the WKT. I presume its violating an OGC rule but not sure what.

GEOMETRYCOLLECTION (GEOMETRYCOLLECTION (POLYGON ((-2.76 49.38905, -2.7600333333333333 
49.535166666666662, -2.5833500000000003 49.5352, -2.4087833333333331 
49.535166666666662, -2.4087666666666667 49.38905, -2.56075 49.389099999999992, 
-2.5552833333333336 49.437733333333334, -2.5552166666666665 49.455183333333331, 
-2.5968 49.455183333333331, -2.5967833333333332 49.437733333333334, 
-2.5552833333333336 49.437733333333334, -2.56075 49.389099999999992, -2.76 49.38905))))

I am unable to change this data so is there an alternative to reading this out of SQL without having to change it?

Thanks for looking

Answer 1

Looks like you have a self-intersection, which SQL Server no likey. I'm surprised it even got loaded into the database in the first place. Try running MakeValid() and see what it does to the shape. You don't have to test it on the original data, just make a new one on the fly in Management Studio.

What's interesting is that SQL Server will plot it:

But it is indeed invalid:

DECLARE @test geometry
SET @test = geometry::STGeomCollFromText('GEOMETRYCOLLECTION(POLYGON((
 -2.76 49.38905,
 -2.7600333333333333 49.535166666666662, 
 -2.5833500000000003 49.5352,
 -2.4087833333333331 49.535166666666662, 
 -2.4087666666666667 49.38905, 
 -2.56075 49.389099999999992, 
 -2.5552833333333336 49.437733333333334, 
 -2.5552166666666665 49.455183333333331, 
 -2.5968 49.455183333333331, 
 -2.5967833333333332 49.437733333333334, 
 -2.5552833333333336 49.437733333333334, 
 -2.56075 49.389099999999992, 
 -2.76 49.38905)))',0)
SELECT @test.STIsValid()

>> 0