Finding OGC WMS, WFS, WCS services
In April, Mike Botts, Botts Innovative Research, Inc. posed a deceptively simple question to an OGC discussion list: “How does one find existing services that implement OGC Web Map Service (WMS), Web Feature Service (WFS), and Web Coverage Service (WCS) interface standards these days?” In response to such a fundamental question came an outpouring of responses on the many ways to find OGC services. How many services do you think were identified?
Marten Hogeweg, Esri, responded that you can search for services on this Geoportal Server with 1300+ WMS's and then some WFS, WCS, Sensor Observation Service (SOS), and Catalog Service – Web (CSW). From there you can direct your searches to a number of other catalogs (not harvested, but federated), including Data.gov, ArcGIS Online, GEOSS, etc. Marten continued that alternatively to a "service type" search, you could also start from a geographic search such as ‘in an area around Alabama’ and ‘about Alabama’. Or do a more specific search including a type filter (map services only), with consider global items overlapping Alabama (in this case a spatial ranking is at play as well as a textual ranking).
Data.gov is the home of the U.S. Government’s open data, where you can find data, tools, and resources to conduct research, develop web and mobile applications, design data visualizations, and more. Data.gov offers a CSW developed by the pycsw team. Searching data.gov CSW for WMS found 3,218 hits. This is the number of WMS servers. Each WMS server contains many map layers.
The Global Earth Observing System of System (GEOSS) includes a GEOSS portal, broker, clearinghouse and registries that provide discovery of Earth Observation resources. Searching the GEOSS Portal for WMS services returns 1698 hits.
Perry Peterson, PYXIS Innovation, extended the discussion about GEOSS by pointing to their crawler of Catalogues, which links to the GEOSS Discovery and Access Broker (DAB). Perry also identified the Spatineo Monitor as an excellent resource. Currently Spatineo monitors availability, usage and quality of 18,445 Spatial Web services with 384,891 known data offerings from around the world. This is a ratio of 20 data offerings per web service.
Wenwen Li, from ASU’s GeoDa Center for Geospatial Analysis and Computation highlighted the crawler they developed as part of an NSF-funded project on Polar Cyberinfrastructure named PolarHub to look on the Internet using a hybrid Google + customized crawling strategy to look for OGC standards, such as WMS, WFS, WCS, Web Processing Service (WPS), and CSW. At this point, they do not limit the geographical extent for service searching, so you will see all services found by the crawler (not only for the polar region). A map shows all services found at different locations.
References to using Google to search for OGC services triggered several messages about the best way to do such a search. Frédéric Houbie, Geomatys, uses Google search with “inurl” parameter. Several other approaches were discussed including the challenge that if you are really looking for “North Alabama area, including primarily standard GIS-type data and weather-related data” that’s an intractable 42M hits! That’s not necessarily a service interface API issue, but depends largely on how your search engine works and what content resides in the catalog you’re searching.
Some may recall the venerable Skylab Mobilesystems WMS server list. That page is still alive with the totals from a few months ago of 994 WMS Servers containing a total of 339,254 layers. That is a ratio of 340 layers per WMS server. This ratio for layers/WMS differs by an order of magnitude from Spatineo’s ratio of data/service, which is not surprising as WMS map layers are more numerous than data layers in WFS/WCS.
You may also recall the “Status of INSPIRE inspired OGC Web Services” presentation by Lopez-Pellicer, et.al, at the INSPIRE Conference 2011. They developed a web crawler for geospatial resources to assess NSDIs’ spatial data services. Their global search found 8,256 OGC web services.
These responses and others to Mike's simple question provide a quick update on the availability of geospatial information accessible in open standards from the OGC.
The take-away and the answer to my question at the beginning of this blog post? Today, on the order of ten thousand discoverable OGC web services are offering hundreds of thousands of maps and datasets.
The key ingredient in these searches, of course, is the OGC Catalog Services – Web Interface Standard. Looking to the future, we anticipate that in the not-too-distant future the OGC's OpenSearch Geo and Time Extensions (see recent press release) will make it easy for anyone to obtain useful information by entering place and time in ordinary web searches.