DB geography type MakeValid does not seem to be working

Question

I have an application where the user draws zones and later I check if a polyline crosses them.

All of a sudden the application crashed out with the error:

A .NET Framework error occurred during execution of user-defined routine or aggregate "geography": 
System.ArgumentException: 24144: This operation cannot be completed because the instance is not valid. Use MakeValid to convert the instance to a valid instance. Note that MakeValid may cause the points of a geometry instance to shift slightly.
System.ArgumentException: 
  at Microsoft.SqlServer.Types.SqlGeography.STIntersects(SqlGeography other)

I was surprised at the message 'Use MakeValid' as I AM using 'MakeValid' as shown below:

Select ZonePolygonId, ZoneName, isHome  FROM dbo.SpatialZonePolygons 
WHERE Coordinates.STIntersects(geography::STGeomFromText('LINESTRING(51.15826 -0.18398, 51.15855 -0.18404, 51.15883 -0.18414, 51.15903 -0.18427, 51.15915 -0.18437, 51.15922 -0.1845, 51.15918 -0.18493, 51.15882 -0.18748, 51.15975 -0.18783, 51.15994 -0.18793, 51.16056 -0.18846, 51.16055 -0.1885, 51.16054 -0.1886, 51.16057 -0.18877, 51.16061 -0.18884, 51.16067 -0.18888, 51.16072 -0.18889, 51.16078 -0.18888, 51.16086 -0.18878, 51.1609 -0.18861, 51.16087 -0.18843, 51.16085 -0.1884, 51.16175 -0.18677, 51.16203 -0.18625, 51.16227 -0.18587, 51.16246 -0.18566, 51.16263 -0.18552, 51.16319 -0.18513, 51.16333 -0.18502, 51.16351 -0.18481, 51.16362 -0.18462, 51.16371 -0.18437, 51.1638 -0.18386, 51.1643 -0.18029, 51.16466 -0.17755, 51.16466 -0.17715, 51.16458 -0.17674, 51.16441 -0.17635, 51.16414 -0.17593, 51.16386 -0.17558, 51.16367 -0.17538, 51.16369 -0.17534, 51.16372 -0.17524, 51.16371 -0.17514, 51.16369 -0.17505, 51.16365 -0.17498, 51.16359 -0.17494, 51.16354 -0.17493, 51.16351 -0.17494, 51.16348 -0.17482, 51.16346 -0.17473, 51.16341 -0.17459, 51.16278 -0.17353, 51.16262 -0.17324, 51.16255 -0.17308, 51.16254 -0.17298, 51.16256 -0.17275, 51.16282 -0.17248, 51.16305 -0.1723, 51.16321 -0.17222, 51.16334 -0.17219, 51.16347 -0.17219, 51.16367 -0.17225, 51.16385 -0.17237, 51.16403 -0.17256, 51.16427 -0.17292, 51.16459 -0.17345, 51.16476 -0.17363, 51.16665 -0.17706, 51.16728 -0.17817, 51.16728 -0.17823, 51.1673 -0.17835, 51.16734 -0.17842, 51.16741 -0.17851, 51.16747 -0.17854, 51.16756 -0.17853, 51.16765 -0.17845, 51.16771 -0.17831, 51.16772 -0.17815, 51.16771 -0.17807, 51.16776 -0.17743, 51.16798 -0.1769, 51.16831 -0.17611, 51.16848 -0.17578, 51.16881 -0.17529, 51.16925 -0.17463, 51.16976 -0.17384, 51.17095 -0.17214, 51.171 -0.17225, 51.17097 -0.17278, 51.17131 -0.1729, 51.17149 -0.17297, 51.17161 -0.17296, 51.1719 -0.17276, 51.172 -0.17265, 51.17208 -0.17246, 51.1722 -0.17178, 51.17225 -0.17151, 51.17229 -0.17143, 51.17241 -0.17132, 51.17272 -0.17129, 51.17297 -0.17124, 51.17332 -0.17118, 51.17341 -0.17118, 51.17347 -0.17124, 51.17352 -0.17136, 51.17368 -0.17199', 4326).MakeValid())>0

I later found the offending polygon (see image) has been drawn pretty badly and I guess this is causing the issue.

So my specific questions are:

1. Am I using MakeValid correctly? I thought MakeValid() would resolve this kind of thing...
2. Obviously I have no control over the drawing skills of my client so if MakeValid doesn't help for badly drawn polygons, is there some other way of er... making this valid?

Many thanks.

Answer 1

OK, so the issue was indeed an invalid polygon zone held in the database.

The 'Use MakeValid' in the error message triggered some wrong assumptions as I was already using MakeValid. Actually this error was triggered from an invalid Polygon zone and not the PolyLine I was using in the query.

To protect against this I have added 'MakeValid()' to the INSERT SQL Statement so that no invalid polygons can ever exist within the database again.

I have tested inserting an invalid polygon with and without 'MakeValid' within the INSERT statement and can confirm adding 'MakeValid' does resolve the issue.

INSERT INTO SpatialZonePolygons (ZoneName,Coordinates) VALUES ('ValidZone',geography::STGeomFromText('POLYGON([SqlFormattedCoordinates here])', 4326).MakeValid())