Urgent needs for territory management drive cities to run for geographical information system. Surface spacial reference data concern territory Real Estate, Country Zoning, Civil Protection, etc. These data are coming from surveyors. It is the Real Estate Registry that corresponds to the surface cadaster. In more, cities need data concerning underground installations drinking water. sewage, electricity electricity, gas, etc. . The former subdivide in three categories: underground cadaster and, details of undeground installations that describes the nature of the material, allows management of the systems (simulation, supervision) and management of the material (replacement stock).
Tecvision SA has developed, to the initiative of a city, a Geographical Information System (GIS) called GEOCAD for surface and underground spacial data management, simulation and supervision of the drinking water system and of the electricity system. GEOCAD, is characterised by its ease of use and the rapidity of database loading.
Spacial reference data of a city exist in general under many methods of procedure :
The database loading is a long breath work, whose cost is several times superior to the cost of a geographical system. This is why GEOCAD has automated and optimized this work from all above mentioned data methods of loading.For example, a thorough survey has evidenced that data loading from plans passed to the scanner is very clearly longer and complicated that recopies it by means of adapted data-processing tools.
The city of Pully covers an area of 594 ha, whose approximately 300 ha are strongly urbanized. (1 ha = 10,000 square meters). The cadaster is splited in 247 maps scaled 1/200 to the format A0(1190mm x 840mm). Approximately 70 % of plans, representing the surface cadaster and the underground cadaster, have been drawn on a plastic Mylar support between 1973 and 1989. In less of 9 month, all existent plans have been loaded in the database by recopying on a digitizing table. Then, it has been necessary near a year, to complete the database from raw data of the geometer and Public Works Department sketches. These works have been undertaken by 3 draftsmen.
Thanks to this database, the commune can extract plans to any scale, or to predefined scales. The user can select any orientation and format. Each department can access his own data elements such that surface cadaster, drinking water system, etc. Work has been completed by loading data for the underground network system simulation and supervision. One of the great benefits of a geographical information system is derived from the possibility to automatically carry forward rectification of surface cadaster on each Public Work service of the city.
The quality of a spacial reference database base depends on the care with which information has been loaded. To obtain an optimum result, GEOCAD uses non-linear data-processing routines, that allow to compensate the deformation of plans caused by the aging as well as humidity and temperature fluctuations.The quality control has been undertaken by comparing triangulation points of the geodetic network, provided by the state geometer and with corresponding points of the database. Thanks to the undertaken compensation, the obtained standard deviation is inferior to 3 cm at scale 1/1 .
GEOCAD software has been built around the powerful Computer Aided Design software AutoCAD. AutoCAD is used by GEOCAD as a "toolbox" of drawing functions, such that :
GEOCAD pilots AutoCAD by a series of functions developed in the artificial intelligence language LISP. Functions are called by the user by means a "mouse" and a "menu" fixed on the digitizing table. For example, a draining is automatically traced, by giving the outgoing point and the point of arrival, as a simple line. Functions are very simple to use because near to the intuitive way to work. The user has not therefore the concern to learn AutoCAD. The cadastral database is extensible practically without limit and the speed of work does not depend on its size. For example it is possible to put on a single standard PC computer, supplied with adequate hard disks the equivalents of 300 km 2 of strongly urbanized surface. Several data servers can be connected in network to form a distributed database of any size. GEOCAD is the result of 5 years - man of work undertaken in narrow connection with geometers and Public Works engineers of the city and is characterised by it very powerfull graphical man - machine interface. GEOCAD use a particularly fast solution to suppress of the drawing of the property limits inside the triangulation symbol.
GEOCAD can be loaded on any PC computer . A digitizing table is compulsory. A high resolution graphic card and corresponding display are highly recommended. AutoCAD is supplied with GeoCAD.
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Last modified: janvier 05, 2006