MsSqlSpatial - Spatial Extensions for SQL Server

MsSqlSpatial is a Spatial Extensions for SQL Server 2005. This project conforms to OGC Simple Features Specification for SQL Revision 1.1 and provides many useful features to power your GIS application. Features:

 * OGC Simple Features Specification for SQL Revision 1.1 conformant (non official but verifiable).
 * 2D Geometries supported: Point, LineString, Polygon, MultiPoint, MultiLineString, MultiPolygon, GeometryCollection.
 * Predicate functions: Equals, Disjoint, Intersects, Touches, Crosses, Within, Contains, Overlaps, Covers, CoveredBy, Relate, IsWithinDistance.
 * Spatial analysis functions: ConvexHull, Intersection, Union, Difference, SymDifference.
 * Linear referencing functions: LineInterpolatePoint, LineLocatePoint, LineSubstring.
 * Spatial relationship and processing functions: Distance, Length, Area, Buffer, Centroid, PointOnSurface, Simplify, Polygonize, LineMerge and many more.
 * Coordinate systems aware: SRID, SetSRID, Transform.
 * Spatial indexing: Simple but effective implementation using table-valued functions (FilterQuery, JoinFilterQuery, IsWithinDistanceQuery, RelateQuery)
 * Aggregate functions that overcome the 8000 bytes limitation of normal user-defined aggregate functions: UnionAggregate, EnvelopeAggregate, IntersectionAggregate.
 * GML support: AsGML function.
 * Import from shapefiles and PostGIS tables. 

Go to http://www.codeplex.com/MsSqlSpatial

See also these related projects.