GML prototype tested for interoperability

PS ACHARYA, RN NANDA AND A SINDAL
The experiment holds the key to addressing the problem of incompatibility between different spatial data sets held by various national mapping agencies

A sample data set from Survey of India (SoI)’s conventional digital topographic data has been converted to Open Geo-spatial Consortium (OGC)’s Geography Markup Language (GML) format and tested for interoperability between different leading commercial GIS packages in a recent GML relay conducted in New Delhi on 27 January 2006. An approach for the development of a sample GML prototype was devised by the Working Group on ‘Interoperability’ chaired by Major General M. Gopal Rao, Surveyor General of India and constituted under the Natural Resources Data Management System (NRDMS) – an R & D Programme of Department of Science & Technology. The experiment holds the key to addressing the problem of incompatibility between different spatial data sets held by various National Mapping Agencies. Overcoming the problem through preprocessing of the data by user agencies has been a tedious, investment-intensive, and timeconsuming task ever since integrated databases began to be built to support developmental planning.

As a part of the exercise, a GML application schema has been developed using OGC’s GML 2.1.2 core schema for the ‘road’ theme of the topographic data of the SoI. The core schema provides for the standard ways various feature data sets need to be encoded for creating application schema for the selected theme. The application schemas are in turn used for preparing GML data by populating the schema with the SoI’s road data, both geometric coordinates and attributes, using Visual Basic. The application schema consists of different classes falling into the road domain like the distance stones, road structures (e.g. bridges, culverts etc.), and roads with their spatial and attribute properties taken from the National Spatial Data Exchange (NSDE) format of National Spatial Data Infrastructure (NSDI). To support formation of the application schema, a class diagram in the Unifi ed Modelling Language (UML) formalism as prescribed by the ISO 19109 has been prepared. ISO 19109 prescribes standard rules for developing application schemas as per procedures of International Standardization Organisation (ISO). The prototype has been tested and
cross-checked for any possible loss of data by graphically displaying the data in Scalable Vector Graphics (SVG).

Validity of the data set has been tested for interoperability by means of a relay conducted on 27 January 2006 at NSDI Offi ce, RK Puram, New Delhi with the participation of vendors who have imported the data directly to their proprietary formats. Outcomes of the test indicate direct portability of the SoI’s GML prototype to the individual vendor packages like Oracle Corporation’s Oracle Spatial, ESRI’s ARC GIS, and Intergraph’s Geomedia. Each vendor has displayed and edited the prototype by addition of a few features and then exported the edited data to GML format. Import and export of the data sets from and to GML format have been observed to be possible. The output GML data coming out of the packages partially vary from the original GML application schema provided initially. Efforts are on to study the variations and upgrade the application schema to accommodate more feature types for testing.

Several organizations including Space Application Centre (SAC), Ahmedabad; National Informatics Centre (NIC), New Delhi; Indian Institutes of Technology (IIT), Bombay, Kharagpur, and Delhi; Ministry of Defence (MoD); National Hydrographic Office (NHO), Dehra Dun have contributed to the deliberations of the Working Group leading to the development of the prototype.

GML defines a data encoding in Extensible Markup Language (XML) for geographic data and its attributes and provides a means for encoding such information for storage and transport over the web. It is extensible and supports a wide variety of spatial tasks, from portrayal to analysis. It separates content from presentation and enables the user to use his presentation style at the end of analysis.

The GML prototype and the relays are expected to throw light on the processes involved in the distribution of conventional geospatial data in the Indian Spatial Data Infrastructures using OGC standards. A strategy for ensuring interoperability between different data providers could be potentially drawn up based on the outcomes and the insights gained in the study.

(Note: Expressions made in this article are solely of the authors and do not in any way reflect the viewpoints of the organizations they are employed with.)