Subtracting a SQL Server geometry from another

Question

Is there a way to subtract a geometry from another? A kind of reverse STUnion..

The problem I am having is that I need to ensure a shape fits within another (without changing the larger shape). I thought I could use the STIntersection to get the shape thats "in". However, STIntersection is not accurate and produces a shape that can (and does) not equate to the true intersection.

You can easily see this if you then take the STDifference of the original shape.

So , what I would like to do is given two shapes I want to subtract one from the other - e.g. Take the STIntersection and then subtract the STDifference.

Any ideas?

Edit: For now, I have created my intersection from a STBuffer(-1) version of the bigger shape, this should account the mathematical variation of STIntersection with a slight reduction in accuracy. However, I would still love to know if you can subtract a geometry from another..

Answer 1

Did you try STWithin?

Answer 2

Just use .STDifference(). No need to intersect first, then subtract the intersection. Just subtract directly.