Navigation-capable maps and plans are printed with a coordinate grid.
In the coordinate grid, the two-dimensional projection of the three-dimensional earth's surface is realized in form of a Coordinate System.
Historically the countries over the world use many different Coordinate Systems.
The earth is not a sphere but a mathematically indefinable geoid and its form can best be described by an ellipsoid. In order to ensure an exact projection of a region in a Coordinate System, the region is first projected onto a so-called Reference Ellipsoid that would fit the region as well as possible. The Reference Ellipsoid is mathematically defined so that a Coordinate System can be mapped onto it. A Coordinate System mapped to a Reference Ellipsoid is called a Coordinate Reference System or commonly abbreviated CRS or also "Geodetic Datum". So it happens that in all countries of the world different and often several small and large-scale, historic and modern Coordinate Reference Systems are used in parallel.
Each country has one or even several of its own historical coordinate and reference systems. In some countries multiple competing systems where used simultaneously. The Federal Republic of Germany is a good illustration of this situation:
Prussian Cadastral Systems
The German surveying with relatively exact maps has its beginning with the development of the Prussian Cadastral Systems, which where established around the year 1880. The projections where done in 40 different Soldner coordinate systems on the reference ellipsoid Bessel. The Soldner projections have their origin each in larger cities at historical places such as churches, castles and government buildings. In the Federal State Berlin a Soldner projection named "Müggelsberg" is still in use.
DHDN (old blocks)
In the old States of the Federal Republic as well as in unified Germany was used, and is still in use, the Potsdam Datum (DHDN) based upon the Bessel Ellipsoid. The projection is normally made into the Geographic Coordinate System or into the Gauss-Krueger Coordinate System with three degrees wide meridian strips. Small-scale maps were often made using various Lambert Coordinate Systems.
The former German Democratic Republic used the System S42/83 based on a Krassowskij ellipsoid and projection into the Gauss-Krueger Coordinate System with six degrees meridian strips.
RD83 / PD83
Some of the Federal Republic new states use the Rauenberg Datum RD83 and the Rauenberg Datum PD83 projected onto the Bessel Ellipsoid. The projection is uniformly made to the old Federal Republic States in the Geographic Coordinate System, or to the Gauss-Krueger Coordinate System with three degrees wide meridian strips.
On the Day of German Unity, October 3rd 1990, representatives of the Basic Surveying of the old and new Federal States developed a draft which had a standardised, geodetic Reference System in the unified Germany as its objective. This could only happen by definition, while connecting the historically grown Reference Systems DHDN, S42/83, RD83 and PD83 described above to a new DHDN90. The DHDN90 can be considered as a Compound Coordinate Reference System (CCRS).
Military topography uses a NATO standard based on the European Datum ED50 with the International Ellipsoid from Hayford and projection to the UTM Coordinate System or to the Military Grid Reference System (MGRS).
Thanks to the growing popularity and wide use of the American satellite-based Navstar GPS (Global Positioning System), internationally and of course within the Federal Republic of Germany, there is increased acceptance of the worldwide WGS84 (World Geodetic System), introduced in 1984. It become even more important after the intentional degradation of the GPS signal was lifted in Mai 2000.
With Galileo, the European satellite navigation system which is operational since 2018 and the modernized Navstar GPS III and GPS IIIF the development of modern satellite navigation will be continued.
Due to the many different Coordinate and Reference Systems of the countries, transnational spatial projects are made considerably more difficult.
On the other hand, the spread of GIS technologies, the increased use of GPS, and the internationalization of trade, politics, and environmental protection require more and more transnational geospatial data.
An important condition for progress in this area is a unified Coordinate System along with a unified Reference System.
The global UTM Coordinate System (Universal Transversal Mercator Projection) with 60 meridian strips can be used worldwide. For Europe, the ETRF89 (European Terrestrial Reference Frame), which was created by combining several modern navigation methods, has been measured and evaluated as the basis for the European Reference System ETRS89 (European Terrestrial Reference System 1989).
In the 1990-ties the Surveying Authorities of most European countries decided to use for extensive topographic and cadastral projects the UTM Coordinate System and the ETRS89 Reference System. It is based on the GRS80 ellipsoid (Geodetic Reference System). UTM coordinates are used for projection in most maps across Europe.
There is another big advantage in moving to the modern Coordinate and Reference Systems. The American Satellite Navigation System GPS data is referenced to the WGS84 (World Geodetic System). WGS84 deviates only slightly from ETRS89, which allows the direct use of GPS coordinates for the enrichment of spatial data and for use in modern maps with only a slight deviation of less than one meter.
Exact datum shifts from DHDN90 to the modern ETRS89 are possible country-wide since 2008 with a gridfile named BeTA2007 that uses the NTv2 standard. Almost all Federal States now have highly accurate NTv2 grid files, some of which can even be used with accuracies in the lower centimeter range for the real estate cadastre.
Planning and executing business and scientific projects, topographical, cadastral and public works, require topographical documentation, maps, blueprints and digital data, containing large amounts of project-related positions and coordinates. As long as the traditional Coordinate and Reference Systems are still used along with the modern systems there will be need for translation of spatial data from traditional systems into the modern Europe and worldwide system. This means that during the transition period there will be a high-volume data processing of geodetic datum shift Coordinate Transformations from traditional systems into the modern systems. The program TRANSDATpro and the Geodetic Development Kit GeoDLL where developed for conversion of spatial data between various Coordinate and Reference Systems across the whole world, as well as for maintenance and storing of spatial data. The software is easy to use, can perform calculations on large amounts of data quickly and with high accuracy. The modern software by the engineering office KilletSoft is able to cover a lot of user requirements thanks to their high flexibility and timeliness.