[Microsoft.SqlServer.Server.SqlFunction]
public static SqlXml ExportToKml(SqlGeography g)
{
    if (g == null || g.IsNull)
        return new SqlXml();

    MemoryStream stream = new MemoryStream();
    XmlWriter writer = XmlWriter.Create(stream);

    KeyholeMarkupLanguageGeography sink = new KeyholeMarkupLanguageGeography(writer);

    g.Populate(sink);

    sink.FinalizeKMLDocument();

    writer.Flush();
    stream.Seek(0, SeekOrigin.Begin);

    return new SqlXml(stream);
}