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GeoInformatics-7-2009
article 2 a short history of relations between geolocation and time common sense tells us that spatial aspects of all existence are fundamental. before an awareness of time, there is an awareness of relations in space. space seems to be that aspect of existence to which most other things can be analogized or with which they can be equated. the concept of spatial relatedness is a quality without which it is difficult or impossible for the human mind to apprehend anything. for this reason, a man in the earliest era of development developed a sense of relations between here and there and wanted to communicate these relations to the others. at the same time, a man wanted to acquire them from these others. the easiest way to do it was through maps. maps constitute a common language used by men of different races and tongues to express the relationship of their society to a geographic environment. maps have changed and developed through history as much as human mind and knowledge did. the ways used to represent and organize these spatial relationships in a form of map changed and developed as well, from the simplest forms up to present sophisticated digital products. astronomy, geodesy, surveying and geography along with cartography, are the sciences that enabled this development. figure 2(a). portrait of galileo galilei (1564-1642), painted in 1636 by j. sustermans. galileo has been referred to as the "father of modern astronomy", as the "father of modern physics", and as the "father of science". (image source: http://en.wikipedia.org). figure 2(b). two of galileo s first telescopes; in the institute and museum of the history of science, florence. in providing a unified reference of a modern global terrestrial reference system. however, since the middle of the 20th century the natural celestial bodies are not the only objects of observation for astronomers and geodesists any more. with the russian sputnik i in the year 1957, we entered into the era of artificial satellites, which has evolved in a few decades to such a level, that the satellite techniques have gained an essential and actually indispensable role in global positioning, navigation and timing. the us global positioning system (gps) and the russian global navigation satellite system (glonass) system were established as global satellite navigation systems (gnss), while the european galileo and the chinese beidou2-compass systems are already in their initial operating phases. all these systems are actually based on the same concepts, i.e. on a constellation of earth orbiting spacecraft emitting signals with precise orbital and time data. suitable receiver equipment combines the signals from at least four spacecraft yielding the time and the three spatial coordinates. in a certain way, the humanity is in a similar position nowadays as it was two and a half centuries ago, when h-4 was made. then the long sought solution of the longitude problem was finally found and put into a mechanical pocket watch to serve the sailors and the public. today, after a long and winding road filled with innumerable new technological inventions, we have reached a point of development, when we are able to put not only longitude, but also latitude, heighth and time solution all together in a small electronic latest news? visit www.geoinformatics.com device to serve positioning, navigation and timing professionals as well as the widest public across the globe. the article outlines in a few glimpses how the geodetic, surveying, positioning and navigation science have come this far and what steps can and should be done in order to allow the humanity to get the best use of knowing the combined geolocation and time data as accurately as possible. due to the limited space of the paper, the presented contents are obviously selective and without a presumption or attempt of historical completeness. 2.1 the shape and the size of earth through the ancient times, several ideas and opinions regarding the shape of the earth were prevailing among scholars, from a slab to a drum- or pillar-shaped world and through figure 3. eratosthenes has used the same specific moment in time the summer solstice on both ends of the arc to measure the central angle and calculate the circumference of the earth. 45 october/november 2009
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