What is geodesy?
Geodesy is the science that deals with the measurement and mapping of the Earth’s surface and the observation of its gravitational field and geodynamic phenomena. People who practice geodesy professionally are called geodesists.
In simple terms, we can say that geodesy is the science that deals with measuring the earth’s surface and presenting that surface by creating plans and maps. It is one of the technical sciences, and it consists of five branches:
- cartography
- photogrammetry and remote sensing
- maritime, satellite and physical geodesy
- applied geodesy
- geomatics
Although these branches of geodesy are relatively well-recognized, each of them has something in common with the others. Geodetic surveying, or simply surveying, is the collection, processing, and presentation of data using geodetic methods. Geodetic methods are methods of collecting, processing, and presenting data that are specific to geodesy, or its branches: cartography, photogrammetry, maritime, satellite, and physical geodesy, applied geodesy, and geomatics.
The most common forms of data collection in geodetic surveying are direct collection – by measuring with geodetic instruments or indirect collection – by measuring images. Geodetic data collection methods include: orthogonal method, polar method or tachymetry, terrestrial and aerial photogrammetry, remote sensing, leveling, trigonometric height determination, global positioning systems (GPS), etc.
Today, we use computers to process collected data, and mathematical processing of measured data usually involves the application of the principles and methods of mathematical statistics, error theory, and equalization calculus. The collected data is further processed and becomes part of various spatial information systems.
The results of the survey are most often displayed on maps. In the past, geodetic surveying was mainly used to determine the mutual position of points on the Earth’s surface and to collect data on the relief and built objects. The development of technical means for collecting, processing and naming data created the conditions for measuring not only land, but also other objects using geodetic methods.
Practical geodesy
Practical geodesy deals with practical measurements of smaller parts of the Earth’s surface for the purpose of producing large-scale maps. Special geodetic methods are used, such as: triangulation, polygonometry, leveling, trigonometric height measurement, detailed surveying, horizontal and vertical stakeouts. These methods require skill in handling geodetic instruments, among which theodolite, level, tachymeter and rangefinder should be highlighted.
Engineering geodesy
Engineering geodesy is a branch of geodesy that deals with the application of geodesy in engineering design and construction of facilities. It includes geodetic networks as a basis for design, staking out and creating geodetic bases for design, geotopographic works, geodetic works in the design, construction and inspection of roads, bridges, tunnels, power lines and hydrotechnical facilities.
Spatial information management
Spatial information management encompasses several different areas such as data and information, information technology, organizational issues and spatial data infrastructure, and is a key factor in solving everyday problems of users related to land and real estate. Land and real estate are gaining increasing importance today, and in order to manage them effectively, they need to be recorded.
The real estate cadastre, a record of not only land but also buildings on it, ensures ownership. Dividing land, establishing boundaries and developing modern information systems to support spatial management by state bodies, local governments, utility companies and other companies is a broad area of activity for most surveyors.
The development of measurement and information technologies has contributed to the emergence of many land information systems, mainly based on data that was previously collected and maintained within the cadastre, and today opens up new possibilities for their more efficient use and ensuring sustainable development.
Photogrammetry and remote sensing
Photogrammetry is the art, science, and technology of obtaining reliable quantitative information about physical objects and the environment through the process of recording, measuring, and interpreting photographic images and scenes of electromagnetic radiation obtained by sensor systems.
Photogrammetric surveying is a surveying method that basically uses images, taken either from the air or from the ground. The results of photogrammetric surveying can be coordinates of individual points, plans and other graphic representations, as well as corrected photographs and photomaps derived from them, photomosaics and panoramic images. Since the image is generally not strictly vertical, the perspective image will be deformed even on strictly horizontal terrain.
The translation of such a deformed image into a corrected image, which will correspond to the orthogonal projection of the land in a certain scale, is called rectification. By differential rectification, it is possible to obtain an image transformed not only into orthogonal, but also into any other projection. The use of images recorded from the air or space using various recording and measurement techniques (photographic, thermal, radar images, radiometric measurements) without physical contact with the recorded object is called remote sensing (remote sensing, Fernerkundung).
By applying remote sensing methods, additional information about the Earth is obtained (geomorphological, geological, pedological, forestry, hydrological, archaeological, etc.).
Geoinformation systems – GIS
A geographic information system (GIS) is a computer system for collecting, storing, processing, analyzing, and displaying spatial data. The four basic components of a GIS are hardware, software, data, and people. People who work with GIS should be computer literate and understand the capabilities that GIS contains and provides. They should also know what cartographers have done to date in the area of analyzing and displaying spatial data.
Geoinformation systems are one of the most promising information technologies of today. Their application should be expected where spatial geometric data needs to be linked with textual, or attribute data (e.g. data on the owner of a cadastral plot, street name and permitted speed limit, etc.) and on that basis, the necessary analyses can be performed. Although GISs themselves are very complex, their use does not have to be that way.
Cartography
A map is a coded image of geographic reality that depicts selected objects or features, created by the creative author’s choice, and used when spatial relationships are of paramount importance. Cartography is a discipline that deals with the creation, production, promotion, and study of maps. General cartography studies the history of cartography, the elements of geographic maps and the way they are displayed on maps, the divisions of maps and atlases, and related cartographic problems.
The theory of map projections or mathematical cartography is a branch of cartography that studies the method of mapping the curved surface of the Earth and other celestial bodies onto a plane. Geodetic cartography deals with mapping parts of the Earth’s surface for the needs of state and detailed surveys. Practical cartography studies the method of making, using and maintaining maps, and the branch of cartography that deals with the reproduction of maps is called map reproduction.
The application of computer technology in cartography is particularly important because the process of map production is complex and very long. In addition, there is a need for an increasing number of diverse maps today, which would not be possible to satisfy with classical production methods.
In addition to accelerating map production, digital cartography has other advantages, such as the possibility of accelerated modernization, reducing production costs, improving working conditions and quality, and solving tasks that were previously impossible to solve.
Higher geodesy and physical geodesy
Since its beginnings, higher geodesy has dealt with problems at the national and regional levels, and has developed in two directions. As mathematical or geometric geodesy, it seeks to find the true shape and size of the Earth, and the geometric body that will most closely resemble the Earth.
In doing so, all the irregularities of the Earth’s crust, hills and valleys, are imagined as projected vertically onto the surface of the sea, extended beneath the land. However, the direction of the vertical, the plumb line, is caused by the attraction of the Earth and individual mountain ranges, and this is investigated by physical geodesy. Both branches, although different in their working methods, are interconnected because in order to determine the attractive effect of the Earth at individual points, it is necessary to know the flattening of the Earth’s ellipsoid, i.e. the dimensions of the Earth. In order to determine the geometric and physical parameters of the Earth’s body – the geoid – as accurately as possible, geodesists use knowledge from related fields of science, such as astronomy, geophysics, gravimetry, etc.
Knowing the exact geoid is very important, because it is used to convert from ellipsoidal heights obtained by GPS to above-sea (orthometric) heights, which are used in water management, construction, and many other activities.
Satellite geodesy and marine geodesy
Modern methods of satellite geodesy have become routine methods in the world in establishing all orders of basic geodetic networks. Classical geodetic measurements of angles and lengths with electro-optical rangefinders for establishing the first and second order national networks are becoming a part of the history of geodesy.
The possibilities of GPS technology have undoubtedly caused the greatest leap in the development of modern geodesy, so many scientists consider the GPS method a revolution in the development of geodetic science. Numerous studies by the most prominent geodetic institutes in the world and in Croatia, as well as experience gained in practice, show that no other method solves the problem of determining the coordinates of points in space as well, economically and reliably as the GPS method.
Marine geodesy provides the basis for various activities at sea that depend on determining positions or on precise measurements on, below or above the sea surface. Areas of research include bathymetry, hydrography, marine gravimetry, geophysics, mean sea level, ocean currents, etc.
Geodetic astronomy
Geodetic experts sometimes have to determine the astronomical coordinates of the viewpoint and the azimuth (direction) to some points on the Earth’s surface in their work. That is why the Faculty of Geodetic Studies studies, among other things, spherical and part of positional astronomy. Previously, geodetic-astronomical measurements were necessary for the spatial placement of first-order trigonometric networks. Today, such measurements are used to determine the shape of the geoid and control geodetic networks above long tunnels.