WFS (Web Feature Server) różni się od WMS tym, że udostępnia dane w postaci wektorowej, wykorzystując do tego format GML. Klient poprzez serwis WFS ma możliwość zamówienia tylko tej partii informacji, która go interesuje. Dzięki wykorzystaniu języka GML klient może lokalnie manipulować otrzymanymi danymi. Istotną cechą tego serwisu jest również umożliwienie edycji danych zgromadzonych na serwerze (jako opcja). Poprzez wysłanie odpowiednich komend klient może usuwać, dodawać lub aktualizować dane po stronie serwera.
Serwis WFS może również stać się klientem innego serwisu WFS. Jeśli jeden z serwerów nie dysponuje zamówionymi przez klienta danymi, WFS może kaskadowo skorzystać z informacji innych serwerów WFS i w rezultacie dostarczyć połączone dane. Serwer WFS powinien obsługiwać następujące żądania:
GetCapabilities - przesyłać opis możliwości serwera; w szczególności musi wskazać, jakie rodzaje obiektów przesyła oraz jakie operacje na poszczególnych obiektach są możliwe do wykonania.
DescribeFeatureType - przesyłać opis struktury obiektów, które obsługuje.
GetFeature - przesyłać konkretne obiekty zgodne z warunkami postawionymi przez klienta i to zarówno atrybutowymi, opisowymi, jak i przestrzennymi.
GetGmlObject - obsłużyć żądanie otrzymania obiektu poprzez odwołanie do XLinks, a także poprzez wskazanie identyfikatora w pliku XML.
Transaction - pozwalać na tworzenie, modyfikację oraz usuwanie obiektów.
LockFeature - pozwalać na zablokowanie jednego lub więcej obiektów na czas trwania transakcji.
The Open Geospatial Consortium Web Feature Service Interface Standard (WFS) provides an interface allowing requests for geographical features across the web using platform-independent calls. One can think of geographical features as the "source code" behind a map, whereas the WMS interface or online mapping portals like Google Maps return only an image, which end-users cannot edit or spatially analyze. The XML-based GML furnishes the default payload-encoding for transporting the geographic features, but other formats like shapefiles can also serve for transport. In early 2006, the OGC members approved the OpenGIS GML Simple Features Profile [1]. This profile is designed to both increase interoperability between WFS servers and to improve the ease of implementation of the WFS standard.
The OGC membership defined and maintains the WFS specification. There are numerous commercial and open source implementations of the WFS interface standard, including an open source reference implementation, called GeoServer. A comprehensive list of WFS implementations can be found at the OGC Implementing Products page
GML - Geography Markup Language - Język Znaczników Geograficznych
Język GML definiuje zbiór elementów przestrzennych (geograficznych) zapisanych w formacie języka XML
Schemat GML - deklaracja zbioru elementów XML, które przeznaczone są do do zapisu określonych własności przestrzennych (geograficznych)
Schemat to nie jest nic innego niż to co już zostało opisane na tej stronie jako XML Schema.
W Polsce zostały już opracowane schematy przeznaczone do przechowywania danych zgodnie z formatem XMLa Np. Topograficzna Baza Danych
The Geography Markup Language (GML) is the XML grammar defined by the Open Geospatial Consortium (OGC) to express geographical features. GML serves as a modeling language for geographic systems as well as an open interchange format for geographic transactions on the Internet. Note that the concept of feature in GML is a very general one and includes not only conventional "vector" or discrete objects, but also coverages (see also GMLJP2) and sensor data. The ability to integrate all forms of geographic information is key to the utility of GML.
GML contains a rich set of primitives which are used to build application specific schemas or application languages. These primitives include:
Geometry
Topology
Time
Dynamic feature
Coverage (including geographic images)
Unit of measure
Directions
Observations
Map presentation styling rules
GeoTools is a free software (LGPL) GIS toolkit for developing standards compliant solutions. It provides an implementation of Open Geospatial Consortium (OGC) specifications as they are developed. GeoTools is a contributor of the GeoAPI project - a vendor-neutral set of Java interfaces derived from OGC specifications - and implements a subset of those.
It is written in Java and currently is under active development. It is used by GeoServer and UDig projects.
WCS (Web Coverage Server) stanowi rozszerzenie specyfikacji WMS. Odnosi się on bardziej do pokrycia terenu posiadającego określoną wartość dla każdego piksela niż do generowania map, jak to ma miejsce w przypadku WMS.
Warto zauważyć, iż otwarty charakter usług Web sprawia, że możliwe i stosunkowo proste jest tworzenie usług dodanych. Jest to jeden z kluczowych czynników mających wpływ na rozwój SDI, pozwala bowiem angażować inwencję i kapitał firm komercyjnych.
GeoServer Features
Fully compliant to WMS 1.1.1, WFS (1.0 and 1.1, transactions and locking) and WCS (1.0 and 1.1) specifications, as tested by the CITE conformance tests. GeoServer additionally serves as Reference Implementation for WCS 1.1 and WFS 1.0 and 1.1
Easy to use web-based configuration tool - no need to touch long, complicated config files.
Mature support for PostGIS, Shapefile, ArcSDE, DB2 and Oracle.
VPF, MySQL, MapInfo, and Cascading WFS are also supported formats.
Native Java support for GeoTIFF, GTOPO30, ArcGrid, WorldImages, ImageMosiacs and Image Pyramids
Support for MrSID, ECW, JPEG2000, DTED, Erdas Imagine, and NITF through GDAL ImageIO Extension. Any format that GDAL supports can be added with a bit of coding.
On the fly reprojection, for WMS and WFS, with an embedded EPSG database supporting hundreds of projections by default.
Web Map output as JPEG, GIF, PNG, PDF, SVG, KML, GeoRSS.
Excellent Google Earth Support, including advanced features like super overlays (vector and raster), 2.5D extrudes, Time, advanced template options for pop-ups and titles, and styling with SLD.
Ability to 'publish' data to Google's geo crawlers, so data from GeoServer can be exposed on Google Maps and Earth searches. (see blog post, docs coming soon)
Integration with GeoWebCache, for accelerated tile mapping (like on Openlayers or Google Maps)
Raw vector data available as GML (2.1.2 and 3.1.1), GeoJSON, and zipped Shapefiles through the WFS.
Anti-aliased images by default, with option to turn off or to use a custom defined palette for increased performance.
Integrated OpenLayers as a default ajax viewer and preview engine.
Standards compliant 'by default' - no need to figure out complex configuration options just to serve basic data.
Performance, on par with the fastest open source mapping servers, and we are quite confident that we do faster rendering than any major proprietary server. See the post on the geoserver blog for more info.
Support for atomic database transactions through the standard WFS-T protocol, available on all data formats.
Versioning WFS to support wiki-style history, attribution, and rollbacks on geospatial data.
Integrated Security through the powerful acegi java framework, to secure individual services and layers to groups of users.
User Interface translated in to French, German, Spanish, Portuguese, Dutch, Japanese, Chinese, Russian and more.
Support for Component WMS / Feature Portrayal Service
Long Transactions through a full implementation of the Locking portion of the WFS specification.
Streaming data readers: no memory bound limit to the amount of data that can be returned.
Full SLD support, the open standard to define map styles, including both user defined (POST and GET) and used natively in styling configuration.
Full Filter support on all data formats in WFS (but optimized for backend format where possible).
Innovative Validation Engine that checks inserted features against a configured set of topological and attributed based rules, to maintain backend integrity.
Java (J2EE) servlet-based, can run in any servlet container. This means we easily support 64-bit architectures and advanced multi-threading capabilities.
Designed for extension, source code that's a pleasure to read.
Easy to write new data formats with GeoTools DataStore interfaces and helper classes, making GeoServer the standards based interface to legacy data.
No need to recompile to support more data formats, GeoTools DataStores instantly plug-in to GeoServer, even showing up as an option in the configuration gui.
Modularized Codebase for pluggable services.
Active Community modules, for developers to experiment with plug-ins before they are ready for core distribution, including modules for REST Configuration API, as well as using REST for User role management and SLD management. Plus CSV and Excel and HTML Image Map
True open source development style, built by a strong community, that you can join and become a part of, tailoring GeoServer for your needs.
Documentation that details everything in easy to understand language.
Featured in books like GIS for Web Developers.
Active email lists for quick support.
Commercial grade installation, support, customization and improvements available from an eco-system of companies, non-profits, and consulting individuals.
more....