Geodetic Database
The Centre for GIS is the custodian of Qatar's geodetic network which consists of approximately 6,000 horizontal control survey monuments and 4,500 vertical control survey stations distributed throughout the country. The primary and secondary networks have recently been upgraded by reobservation with precise Global Positioning System (GPS) readings. These monuments are used by a variety of disciplines, in order to achieve a much higher level of positional accuracy in the surveys, maps, plans and other spatial products they produce than would otherwise be possible.
It is this geodetic network that provides the accurate framework upon which Qatar's digital base maps, Orthoimagery and digital elevation model are structured.
The Centre for GIS has accurately defined The Qatar National Datum (QND95) and provides exact transformation parameters between QND95 and WGS84 and vice versa.
GPS Base Station
Civilian uses of the Global Positioning System (GPS) are outstripping the military uses for which the U.S. Department of Defense initially created the system. In Qatar, government agencies, private companies and individual citizens are making wide use of GPS receivers. The Centre uses GPS extensively to ascertain the location of any new buildings or other cultural features in order to continuously update its Digital Topographic Database.
Unfortunately for civilian users, the U.S. Department of Defense has built in a Selective Availability Program, that for security reasons, renders less accurate the values displayed on civilian GPS receivers.
To overcome this dilemma, The Centre for GIS maintains an active GPS Base station, located on the roof at The Centre, from which it continuously broadcasts differential GPS corrections that provide GPS users, within the cities of Doha and Rayyan, with sub-metre positional accuracy in real time. The Centre also provides an electronic bulletin board service through which users can download actual GPS readings, of the base station, for post processing their own data.
