Unique capabilities for storage and retrieval of geospatial data

Geographic Information Systems (GIS) applications are proliferating throughout organizations involved in natural resource and facilities management as well as general business enterprises. The need for managing the geographic data associated with these systems directly in enterprise database management systems has long been recognized.

Informix Geodetic and Informix Spatial DataBlade modules manage spatial data using different GIS technologies. The Informix Geodetic DataBlade module is best used for global datasets and applications. The Informix Spatial DataBlade module is best used for regional and local datasets and applications.

Combined with the IBM Informix Dynamic Server, the Informix Geodetic DataBlade module provides the capability to manage geospatial information referenced by latitude/longitude coordinates, to support global space- and time-based queries without the limitations inherent in map projections and to achieve high precision regardless of global location. This module is fundamentally different from the flatplane-based IBM Informix Spatial DataBlade module and IBM DB2 Spatial Extender.

Why manage spatial data in an object relational database?

As a server extension, a DataBlade module typically extends the server to manage a new data domain, such as geospatial data. DataBlade modules offer advantages of objectrelational database management systems (ORDBMS), including:

• Uses standard structured query language (SQL). You won't need to learn a new language.
• Simplifies client applications . functions are callable from SQL. Client applications do not have to be re-linked with new versions of the source code. If the client runs on one machine architecture and the database on another, the IBM Informix server automatically performs any required conversion for transporting data between architectures.
• Manages complex data. complexity of processing new data is pushed into the server.
• Ensures data integrity as part of the server, the DataBlade provides concurrency control and transaction management, backup and recovery, and any triggers that you create to enforce local rules.
• Improves performance . scales for multiple users far better than fat client applications do.

Projections

For centuries we have relied on maps, pieces of parchment or paper that graphically depict the features of the Earth. Supporting that practice, many mathematical methods have been developed for representing shapes on the surface of a sphere as shapes on a flat plane. This process is called projection.

Just as you cannot flatten an orange peel without tearing it, you cannot project shapes without distorting them. Every projection distorts distances, shapes (angles) and areas; different methods may minimize the distortion of one of these, but at the expense of the other two. Look at a world map showing Greenland, for example; it is nearly the size of South America. In reality, Brazil's area alone is almost four times Greenland's. Worse, every projection has a limited area where it is valid; and every map has edges.

The computer can construct a virtual globe at any scale. Therefore, it is no longer necessary to tolerate the edges and distortions imposed by projected maps. Most new data is collected using worldwide systems such as global positioning satellite (GPS) and represented in latitude/longitude coordinates. Data management systems work better when they keep the data in this unprojected form, leaving projections where they belong: in the components that display and print maps.

The real distance between two points on Earth

On the Earth's surface, the shortest path between two points is not a straight line; it is an arc, owing to the curvature of the Earth. Geospatial search and manipulation engines that handle flat-plane geometry must approximate the round surface of the Earth by projecting the surface onto flat planes using various transformations. These projections introduce distortions, which can be kept within acceptable bounds only by limiting the area covered by each map.

You expect your database to compute accurate distances and areas, and do it efficiently. The Informix Geodetic DataBlade module is the only product that was originally designed and engineered to work with geodesics and calculate their length without resorting to special-case, computationally inefficient equations.

A spherical solution to model a spherical problem

To handle objects defined on the Earth's surface with precision, the Geodetic DataBlade module uses a latitude and longitude coordinate system on an ellipsoidal Earth model, or geodetic datum, rather than a planar, x- and y-coordinate system. This avoids the distortions, inaccuracies and imprecision that are inevitably introduced by projections. The IBM Informix Geodetic DataBlade module provides a unique and cost-effective solution for global, spherical coordinate (latitude/ longitude-based) problems. This particular DataBlade is unique to IBM and provides significantly reduced development cycles because it models a spherical problem with a spherical solution.