OGC WMS, WFS, and WCS Services (RPM)

OGC--open Geospatial consortium--Open Geographic Information Alliance, is a nonprofit voluntary international Organization for Standardization, leading the development of geospatial information standards and positioning basic services in the field of spatial data interoperability, The interoperability method based on the public interface access pattern is a basic operation method. Through the International Organization for Standardization (ISO/TC211) or technical alliance (such as OGC) to develop the interface specification of spatial data interoperability, GIS software developers to follow this interface specification of spatial data read and write functions, can achieve the interoperability of heterogeneous spatial database. spatial Data Interoperability based on HTTP (WEB) XML is a very popular research direction, mainly related to WEB service technology. OGC and iso/tc211 jointly launched a Web services (XML)-based Spatial data Interoperability Implementation Specification Web Map service,web Feature service,web Coverage Service and Geographic Information Markup Language GMLfor spatial data transfer and conversion.

Web Map Service

the Web Map Service (WMS) makes maps using data with geospatial location information. the map is defined as the representation of geographic data visibility. This specification defines three operations:getcapabitities returns service-level metadata , which is a description of the content and requirements parameters of the service information; Getmap returns a map image whose geospatial reference and size parameters are clearly defined; getfeatureinfo (optional) returns information on some of the special features displayed on the map.

Web Feature Service

The Web Map service returns a map image at the graph level, and the Web feature Service (WFS) returns the feature-level GML encoding and provides transactional operations such as adding, modifying, and deleting features, further deepening the Web map service. the OGC Web feature service allows clients to obtain geospatial data using Geographic Markup Language (GML) encoding from multiple Web feature services, which defines five operations: Getcapabilites returns the Web feature service performance description document (described in XML) ; Describefeaturetype returns an XML document that describes any feature structure that can provide a service; Getfeature serves as a request to get a feature instance; Transaction service for a transaction request ; Lockfeature handles the request to lock one or more feature type instances during a transaction.

Web Coverage Services

The Web Coverage Service (WCS) targets spatial imagery data , which exchanges geospatial data that contains geo-values as "overlays" on the web. The network coverage service consists of three operations: Getcapabilities,getcoverage and Describecoveragetype. The getcapabilities operation returns an XML document that describes the service and data set. The getcoverage operation in a network coverage service is performed after getcapabilities determines what queries can be executed and what data can be obtained, and it returns the values or attributes of a geographic location using a common overwrite format. The Describecoveragetype operation allows a client to request a full description of any overlay provided by a specific WCS server.

The above three specifications can be used as the spatial data Service specification for Web services, but also as the interoperability of spatial data to implement the Far East. as long as one GIS software supports this interface and is deployed on the local server, other GIS software can get the required data through this interface. From the perspective of technology implementation, Web services can be understood as an application that exposes an interface that can be called through the web, allowing programs to be called by any platform, any system, in any language. This application can be implemented in a variety of existing programming languages. The greatest feature of Web services is the interoperability of cross-platform, cross-language, and cross-hardware, and it is the SOAP,WSDL , and UDDI in Web services that guarantee the cross-platform interoperability of Web services, so How you use SOAP, WSDL, and UDDI to deploy, describe, transfer, and register a Web service is key to implementing Web services. Because SOAP, WSDL, and UDDI are a set of standards, different vendors can have different products that implement these standards, such as Sun, APACHE, IBM, Borland, and so on, the Java platform-based Web Services Toolkit, as well as Microsoft's proposed. NET platform, which provides a convenient tool for the development, deployment, and description of Web services, greatly reducing the complexity of developing web services.

Three geographic reference information models: WMS,WFS,WCS

OGC1999 begins WMT1 (Web Map tested) and WMT2 interop projects. One of the famous GML comes from WMT1 's results. In WMT2, the OGC defines three geographic reference information models: Web Map Server (WMS), Web Feature Server (WFS), Web Coverage Server (WCS).

1.Web Map Service (WMS)

the ability to return maps based on the user's request (including raster forms such as png,gif,jpeg or vector forms such as SVG and Web CGM). the WMS supports network protocol HTTP, and the operations that are supported are defined by the URL.

There are three important operating getcapabilities,getmap,getfeatureinfo.

Getcapabilities returns service-level metadata.

Getmap returns a map image.

Getfeatureinfo returns information on some of the special features displayed on the map.

There are some other operations such as Describelayer,getlegendgraphic,getstyles,setsytles. In fact, the traditional point of view, Getmap obtained is in the desktop program in the control of the results, is the performance of the data.

Getfeatureinfo is easier to understand, it and almost all desktop programs are used on the same information button function, are used to get the screen coordinates somewhere, the parameters in the Getfeatureinfo are screen coordinates, the current view range, to a certain extent also facilitates the client's writing. Getfeatureinfo can return feature information from multiple layers at the same time, which is the same as ArcGIS desktop. The WMS also includes requests to return legend information, such as getlegend, and is defined entirely by the existing standards on the desktop.

2.Web feature Services (WFS)

Support for the insertion, update, deletion, retrieval, and discovery services of geographic features. The service returns GML data based on HTTP client requests.

Its base interface is: Getcapabilities,describefeaturetype,getfeature

Getcapabilities Ibid.

Describefeaturetype returns the feature structure for the client to query and other operations.

Getfeature can return a GML compliant data document based on the query request. Getfeature is the most important interface.

Other interfaces such as transaction it not only provides feature reading, but also supports online editing and transactional processing of features.

WFS corresponds to conditional query functionality in common desktop programs, and WFS constructs query conditions through the OGC filter, supports query based on spatial relations, domain-based queries, and, of course, common queries based on spatial relationships and attribute domains.

On the web, WFS requests are not implemented in SQL, but are implemented through the filter XML, which is more extensible. The WFS returns the result set of the query, which, to some extent, differs from the "performance of the data" of the WMS, and the WFS result set is a result set defined and constrained by the complete schema, with GML as the carrier. This result set is a data table similar to the results of a desktop program query.

3.WEB Geographic Coverage Service (WCS)

Provides a spatial raster layer that contains geo-location information or properties, instead of access to a static map.

Send appropriate data, including imagery, multispectral imagery, and other scientific data, based on HTTP client requirements.

There are two important operations Getcapabilities,getcoverage

Getcapabilities returns a description of the service and XML document from which the overwritten data collection can be obtained.

Getcoverage is executed after the getcapabilities determines the query scheme and the data that needs to be fetched, returning the overwrite data.

There is also an optional operation Describecoveragetype.

The WCS corresponds to the raster-based capabilities of the WMS based on the characteristics of the vector data.

Another:Web processing Server (WPS) is the newly introduced standard, its function actually we already familiar with. Processing is the geoprocessing in ArcView, such as Union,intersect. What WPS wants to do is expose a URL-based interface to implement a client's call to such a method via WebService and return data.

These specifications are largely supported in major GIS platforms and open source GIS software.

Intergraph has already launched a WFS server and interop development package.

ESRI has developed related components in ArcIMS that support specifications such as WMS,WFS.

MapInfo8.5 has also increased access to WMS and WFS Services, as well as an excuse to read GML data.

The geoserver,mapserver Map Server plays the role of providing map services to clients in the network. Such map servers can receive a uniform specification of WMS and WFS requests (request), returning data in multiple formats. This process has a strict WMS/WFS specification, so that the client's implementation of the map server is nothing to cause too much impact. Such a specification creates the possibility for a public, federated map Service.

Openlayers/mapbuilder,udig,qgis These client software is divided into browser and desktop client program two kinds. The b/S system client, represented by Openlayers, is now very powerful and can encapsulate WMS requests and implement tile loading capabilities for maps on the browser. In addition, drag and zoom are also very well-equipped to achieve cross-browser operation. The most recent version of Openlayers also supports vector editing, which can be submitted via WFS-T. Traditional desktop client programs are much more powerful, supporting a variety of data sources, including WMS and WFS, plus the ability to edit and operate more powerful than the browser.

Reference: Web Map services for world map maps:

http://www.tianditu.cn/doc/services/index.jsp

OGC WMS, WFS, and WCS Services (RPM)