> No: the difference algorithms outputs a multi-polygon, and not a polygon. The multi-polygon does not contain any polygons, and is a valid geometry. So the output is valid.

 

Thank you, that’s the key that I missed.

 

> No, if the input is valid, the output should be valid too. If it is not valid, these cases may be reported.

 

Perfect.

 

Thanks again

   Volker