- Tuesday, 17 July 2012 10:25
Richard Groom, ARICS and Technical Editor of Geomatics World introduces some of the key technologies and disciplines in the location sector.
Don't you mean land surveying? Yes, but modern land surveyors do a lot more than measure land. Geomatics is a modern term that embraces traditional as well as new surveying applications. It reflects the digital and engineered systems age of GPS and GIS.
Geomatics covers measurement of the size, shape, position and characteristics of the Earth itself and objects on, above and below the Earth. As well as measuring, surveyors also analyse and present spatial data.
You will find surveyors everywhere: in mines, fields, roads, railways, rivers, airports, buildings and even in places you would not expect to find them – like film sets. The discipline is now a slick business in which vast quantities of 3D data can be collected very quickly and inexpensively. This has put Geomatics right at the centre of the information revolution.
Laser scanners can collect vast amounts of 3D data very quickly. The laser itself measures distance from the instrument to the first object that the laser hits. In the scanner, the laser rotates around two axes if it is mounted on a tripod, or one axis if it is on a moving vehicle (mobile laser scanning). For the scanner to calculate the 3D coordinates of the data it captures, it also needs to record the angle in which the laser is pointing and the position, orientation and attitude of the scanner itself. A laser scanning system will therefore incorporate other land surveying techniques, like GPS, to find the sensor's position and, if the scanner is on a vehicle there will be an inertial measurement unit consisting of gyros and accelerometers to measure the tilts in the sensor platform.
If you put a laser scanner in an aircraft, it is normally called LiDAR – Light Detection And Ranging or Aerial LiDAR. The LiDAR scanner points downwards and rotates from side to side to cover a swathe beneath the aircraft. In other respects it is generally the same as a terrestrial scanner.
What about the laser scan data? Well, it's a lot of 3D dots. Each dot has very little intelligence, so the smart part of the scanning process is the software that is used to identify surfaces, edges and other features from the dots.
Geodesy is the scientific study of the size and shape of the Earth. For surveyors and even for every satnav owner, geodesy makes the link between satellite positioning systems such as GPS and the map coordinate systems that we use. The global positioning systems use a global definition of the size and shape of the earth. Before GPS, surveyors developed national coordinate systems with the aim of achieving a good fit for the mapping over their own country. Get the transformation between the two systems wrong and your satnav could think it's on a different road. That's everyday geodesy, but geodesy is a scientific discipline and geodesists measure and research the factors that affect the size and shape of the Earth – like gravity anomalies and crustal movements including earthquakes.
Geographical Information Systems are digital systems that store mapping and geographical related data. They allow users to efficiently analyse, manipulate and perform functions to investigate relationships between the data. GIS can be used, for example, to determine travel distances from homes to schools. That information can be used to determine catchments, eligibility for bus transport to work or for planning new schools.
GIS started as the preserve of large bespoke software systems, but spatial analysis tools now appear in many places and so the 'system' aspect of GIS is becoming less relevant and the term is often shortened to just 'GI'.
Crowdsourcing is a method of data collection which involves collation of data from many sources to make one large dataset. The data may be sent by individuals consciously or transmitted automatically by sensors such as a mobile phone or satnav.
Wikipedia is the best-known crowdsourced dataset but in the geospatial world, OpenStreetMap has made a dramatic impression. With this product, local groups arrange mapping parties in their spare time using hand-held GPS sets to survey streets and send their data to the site free of charge. Using crowdsourcing, the combined dataset can accumulate quickly and at very low cost. There are issues of course, such as completeness, currency and quality control, which can limit the use of crowdsourced data for business and commercial purposes. Emergency services, for instance, need the most up-to-date and accurate mapping to ensure rapid response.
Hydrographic surveying is the mapping of underwater features. It generally refers to the open sea, but is equally applicable to lakes and rivers. Surveyors use acoustic echo sounders to measure the distance from a transponder mounted in a vessel to the seabed. The time taken for the sound pulse to travel from the transponder to the seabed and back is affected by temperature and salinity of the water, so the equipment has to be calibrated carefully.
Over the past ten years, single beam echo sounders that point only vertically down beneath the boat have been largely overshadowed by multibeam echo sounders, which scan a swathe across the seabed and produce a 3D image – not unlike a laser scan. As with laser scanning, the echo sounder has to be positioned. This function is usually carried out using GPS and an inertial measuring unit containing gyros and accelerometers to measure the attitude and velocity of the vessel.
If you've found the topics above interesting, you may want to subscribe to one of the three following publications:
GW is the leading journal for professional and technically qualified surveyors. GW is published under licence from the RICS.
Engineering Surveying Showcase
Showcase goes to over 6,000 engineers, surveyors and other professionals working in construction and development.
GiSPro is the leading journal for for senior professionals and managers developing and using geographical information systems.