Concepts of OGC, WMS, WFS, and WCS

1. OGC

Open Geospatial Consortium is a non-profit International Standardization Organization that leads the development of spatial geographic information standards and positioning basic services in the field of spatial data interoperability, the interoperability method based on the public interface access mode is a basic operation method. Through the International Organization for Standardization (ISO/tc211) or the technical Alliance (such as OGC) to develop interface specifications for spatial data interoperability, GIS software vendors develop spatial data read/write functions that follow this interface specification, it can achieve interoperability between heterogeneous spatial databases. HTTP (Web) XML-based spatial data interoperability is a hot research direction, mainly involving web service related technologies. OGC and ISO/tc211 jointly launched the spatial data interoperability Implementation standard Web Map Service and web feature service based on Web Service (XML, web Coverage Service and the Geographic Information Markup Language (GML) for spatial data transmission and conversion.

2. Web Map Service (WMS)

Use data with geographical location information to create a map. The map is defined as the visualized representation of geographical data. This specification defines three operations: getcapabitities returns service-level metadata, which is a description of the service information content and required parameters; getmap returns a map image, the geospatial reference and size parameters are clearly defined. getfeatureinfo (optional) returns information about some special elements displayed on the map.

3. Web element Service (WFS)

The Web Map Service returns layer-level map images. The Web element Service (WFS) returns the element-level GML code and provides transaction operations such as adding, modifying, and deleting elements, it is a further in-depth study of the Web Map Service. The OGC Web element service allows the client to obtain geospatial data encoded using the geographical Markup Language (GML) from multiple Web element services. This defines five operations: getcapabilites returns the Web element Service Performance description document (described in XML); describefeaturetype returns the XML document describing any element structure that can provide services; getfeature provides services for requests to obtain element instances; transaction provides services for transaction requests. lockfeature processes locks requests to one or more element types during a transaction.

4. Web Coverage Service (WCS)

For spatial image data, it refers to geospatial data that contains geographic location values as "coverage" for mutual exchange on the Internet. The Network Coverage Service consists of three operations: getcapabilities, getcoverage, and describecoveragetype. The getcapabilities operation returns the XML document describing the service and dataset. The getcoverage operation in the network coverage service is performed after getcapabilities determines what kind of query can be executed and what kind of data can be obtained. It uses a common overwrite format to return the value or attribute of a geographical location. The describecoveragetype operation allows the client to request a full description of any overwriting layer provided by a specific WCS server.

 

the preceding three specifications can be used as the Spatial Data Service Specification for web services and as the interoperability of spatial data. As long as a GIS software supports this interface and is deployed on a local server, other GIS software can obtain the required data through this interface. From the technical implementation perspective, you can understand web services as an application Program , it exposes an interface that can be called through the Web to allow calls by programs written in any language on any platform or system. This application can be implemented using various programming languages . The biggest feature of web services is that they can achieve cross-platform, cross-language, and cross-hardware interoperability. SOAP, WSDL, and UDDI in Web Services ensure cross-platform interoperability of Web Services, how to deploy, describe, transmit, and register a web service using SOAP, WSDL, and UDDI is the key to implementing Web Services. Since SOAP, WSDL, and UDDI are a set of standards, different vendors can have different products that implement these standards, for example, the Java-based Web Service toolkit launched by Sun, Apache, IBM, Borland, and other companies, as well as the Web Service toolkit proposed by Microsoft.. NET platform. These tools provide convenient tools for developing, deploying, and describing Web Services, greatly reducing the complexity of developing Web Services.