Postgis types

I've started to implement the most common geometric features of Postgres Spatial Extension as Npgsql Types to easily manage them in npgsql commands. I use it in some private projects, but this is always work in progress. It will be great to have some feedback.

Thanks !

[addendum] Code tested with .NET 4.5 and PostgreSQL 9.1 + Postgis 2.0
It would be ideal if we could check in some way that PostGis is installed before calling postgis_version(). One idea that comes to mind, is to check whether a PostGis type was found in the type loading phase; if so it means PostGis is installed, right?

If you're OK with doing it this way, then let me look at the refactor of the type loading as I described below (i.e. load all types from Postgresql rather than loading only a preset list. Then you'll simply be able to check whether the PostGis type is mapped to a Postgresql OID. Sounds good?