MapInfo Pro provides a Web Feature Service (WFS) client to retrieve geospatial GML data (Geography Markup Language) using HTTP GET and HTTP POST requests over the Internet or through a private intranet. The WFS client was developed in accordance with the 1.0.0, 1.1.0 and 2.0 OpenGIS® Web Feature Service Implementation Specifications, which are available online at: http://www.opengeospatial.org/standards/wfs.
The WFS client supports GML 2 and GML 3. The client returns GML 3 by default when using WFS 2.0 or 1.1.0, and returns GML 2 when using WFS 1.0.0. The OGS WFS Specifications state that all servers should support GML2, but may also support other formats. The server provides information on the formats available, and the client makes the request for the data in the format it can use. If the server does not support GML 2 or GML 3, it will not be supported by the MapInfo WFS client.
WFS is similar to WMS (Web Mapping Service), in that both can provide geographic data via the Internet. But while a WMS server provides raster maps, a WFS server provides raw coordinate data that the client uses to produce a map.
A WFS request contains a description of query operations that can be applied to one or more features. The client generates the request and posts it to a WFS using HTTP. The web feature server then reads and executes the request.
The GetCapabilities operation queries the WFS server for capabilities. Then the MapInfo Pro WFS client can generate a query appropriate for the WFS server and table.
Each table in the WFS server can result in a single MapInfo table. The mapping is always 1-to-1 (unlike WMS, which is many-to-1). The TAB file retrieved from a WFS server resembles a read-only DBMS linked table. It contains a MAP file and a DAT file, and acts like a read-only native table. Information is stored so that the table can be refreshed from the WFS server. GML does not contain any style information. You can provide style information to associate with a particular WFS table.
The sequence of actions can be summarized as follows:
- After sending a GetCapabilities request to a WFS server, the server returns a list of WFS layers (FeatureTypes) that it can provide.
- The user picks a WFS layer to fetch from the server, MapInfo Pro then sends a DescribeFeatureType request to the server. This response is an XML schema that describes the feature.
- The user can then select which columns and/or rows to fetch.
- MapInfo Pro sends a GetFeature request to the WFS. If the user did not select a subset of columns, all columns will be requested by default.
- The response is a GML document containing the feature collection. Each feature represents one "record" in the MapInfo table.
There is a list of WFS servers in the client to help you get started in using this functionality.