Servidor de objetos geográficos para Internet basado en las especificaciones del Consorcio Internacional OpenGis
Fecha
2005-07-20
Autores
Herrera Gonzalez, Osmany
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Editor
Universidad Central “Marta Abreu” de Las Villas
Resumen
El Servidor de Objetos Geográficos (WFS, por sus siglas en ingles) es la
especificación de Interfase de OpenGIS, liberada en Septiembre del 2002 que
permite al cliente obtener datos geoespaciales codificado en GML (Geography
Markup Language) desde múltiples servicios de objetos en Web; similar al Servicio
de Mapas en Web (WMS), que permite al cliente obtener imágenes de mapas para
ser visualizados por múltiples servicios de mapas en Internet.
El WFS habilita tecnologías para el acceso directo a objetos geográficos en
almacenes de datos remotos y distribuidos en un formato estándar.
Permite acceder de forma directa a objetos geográficos como Puntos, Líneas y
Polígonos, bajo el uso de restricciones espaciales o temáticas.
Un WFS implementa las operaciones GetCapabilities, DescribeFeatureType y
GetFeature y es considerado un WFS de solo lectura, el cual es el primer paso para
llegar al WFS de Negociación o Transacional que no es más que un WFS básico
que implementa la operación Transaction (Insert, Delete, Update y LockFeature).
La operación GetCapabilities devuelve un documento XML que brinda información
sobre el servicio, la lista de solicitudes que el WFS puede manipular, el listado de
tipos de objetos que están disponibles en el WFS y las operaciones definidas para el
filtro, en caso de que este exista.
La operación DescribeFeatureType devuelve el esquema en XML que describe la
estructura de todos los tipos de objetos que el WFS puede manipular.
La operación GetFeature devuelve un documento GML que sirve las instancias de
objetos solicitadas en la consulta al WFS.
La operación Transaction es usada para describir las operaciones de
transformación de los datos que son aplicadas a las instancias de objetos accesibles
por la Web. El WFS puede realizar la operación de Transaction directamente o
traducirlo al lenguaje del gestor de datos con el cual se conecta y esta¡ e asu vez
ejecutar la transacción. Al ser completada la operación, el WFS genera como
Servidor de Objetos Geográficos
Autor: Osmani Herrera González
Grupo de Desarrollo de Software GeoMIX 3
respuesta un documento XML, indicando el estado de completamiento de la
transacción.
Esta implementación es un paso lógico para describir las operaciones de
manipulación de datos en objetos geográficos, usando el protocolo http, la cual
incluye la habilidad de obtener o consultar objetos basado en restricciones
generadas por el cliente y pasadas al WFS usando este protocolo. Esto brinda la
factibilidad técnica de acceder a la información ubicada en diferentes almacenes de
datos y la facilidad de usar estas factibilidades técnicas para presentar los datos al
cliente en una aplicación visual, útil y significativa como son los servidor de mapas
basado en las especificaciones de OpenGis; como es el caso el servidor de mapas
desarrollado por nuestro grupo.
A Web Feature Server is the Open GIS Interface specification, liberated in September of the 2002 that allows a client to retrieve geospatial data encoded in Geography Markup Language (GML) from multiple Web Feature Services, similar to the Service of Maps in Web (WMS) that allows the client to overlay map images for display served from multiple Web Map Services on the Internet. The WFS enables technologies for the direct access to geographical objects in remote and distributed data base. It allows direct access to a geographical object as Points, Lines and Polygons, under the use of space or thematic restrictions. A WFS implements the GetCapabilities, DescribeFeatureType and GetFeature operations and it is a readonly WFS. This is the first step to arrive to the Negotiation or Transacional WFS, which is WFS that implements the operation Transaction (Insert, Delete, Update and LockFeature). GetCapabilities A web feature service must be able to describe its capabilities. Specifically, it must indicate which feature types it can service and what operations are supported on each feature type. DescribeFeatureType A web feature service must be able, upon request, to describe the structure of any feature type it can service. GetFeature A web feature service must be able to service a request to retrieve feature instances. In addition, the client should be able to specify which feature properties to fetch and should be able to constrain the query spatially and non-spatially.Transaction A web feature service may be able to service transaction requests. A transaction request is composed of operations that modify features; that is create, update, and delete operations on geographic features. This implementation is a logical step to describe the operations of manipulation of data in geographical objects, using the protocol http, which includes the ability to obtain or to consult objects based on restrictions generated by the client and pass to the WFS using this protocol. This offers the technical feasibility to access to the information in different data bases and the easiness of using these technical feasibilities to present the data to the client in a visual, useful and significant application as they are the maps server, based on the OpenGis specifications; for example the maps server developed by our group
A Web Feature Server is the Open GIS Interface specification, liberated in September of the 2002 that allows a client to retrieve geospatial data encoded in Geography Markup Language (GML) from multiple Web Feature Services, similar to the Service of Maps in Web (WMS) that allows the client to overlay map images for display served from multiple Web Map Services on the Internet. The WFS enables technologies for the direct access to geographical objects in remote and distributed data base. It allows direct access to a geographical object as Points, Lines and Polygons, under the use of space or thematic restrictions. A WFS implements the GetCapabilities, DescribeFeatureType and GetFeature operations and it is a readonly WFS. This is the first step to arrive to the Negotiation or Transacional WFS, which is WFS that implements the operation Transaction (Insert, Delete, Update and LockFeature). GetCapabilities A web feature service must be able to describe its capabilities. Specifically, it must indicate which feature types it can service and what operations are supported on each feature type. DescribeFeatureType A web feature service must be able, upon request, to describe the structure of any feature type it can service. GetFeature A web feature service must be able to service a request to retrieve feature instances. In addition, the client should be able to specify which feature properties to fetch and should be able to constrain the query spatially and non-spatially.Transaction A web feature service may be able to service transaction requests. A transaction request is composed of operations that modify features; that is create, update, and delete operations on geographic features. This implementation is a logical step to describe the operations of manipulation of data in geographical objects, using the protocol http, which includes the ability to obtain or to consult objects based on restrictions generated by the client and pass to the WFS using this protocol. This offers the technical feasibility to access to the information in different data bases and the easiness of using these technical feasibilities to present the data to the client in a visual, useful and significant application as they are the maps server, based on the OpenGis specifications; for example the maps server developed by our group
Descripción
Palabras clave
Servidor, Objetos Geográficos, Internet, Mapas en Web, Especificaciones, Consorcio Internacional OpenGis, Sistemas de Información Geográfica (SIG)