EUGENE McGOVERN offers an update on the technologies that have revolutionised land surveying in recent years.
The term geomatics was introduced in the 1990s to incorporate the older field of land surveying along with the many other aspects of spatial data management that have arisen in recent years. Following the advanced developments in digital data processing, the nature of the tasks required of the professional land surveyor has evolved and the term ‘land surveying’ no longer accurately covers the whole range of tasks that the profession deals with. As society becomes more complex, information with a spatial position associated with it becomes more critical to decision-making from a personal, business, community and governmental perspective. Geomatics practitioners design, develop and operate systems for collecting and analysing spatial information about the land, the oceans, natural resources and man-made features. This article presents the significant developments that have taken place in positioning technology in recent years.
Rise of the machines
The positioning equipment that surveyors use today has gone through a range of changes, from tapes, levels and theodolites, to electronic distance measurement (EDM) devices, total stations, and global navigation satellite system (GNSS) receivers. The equipment is continually advancing.
For example, the humble levelling staff now has a barcode instead of graduations. The barcode is read by a digital level with the operator merely pointing the level towards the staff. The readings are stored electronically and all calculations are carried out automatically (Figure 1).
The total station combines an EDM device with a digital theodolite to provide a single instrument capable of measuring distances and angles simultaneously. The latest total stations are motorised and robotic, i.e., they can locate, lock on to and follow their target automatically. This means that the surveyor is freed up to walk the site and decide where best to locate the target. Other features of the latest total stations include the incorporation of long-range reflectorless EDMs and imaging capability (Figure 2).
A new technology to emerge in the 1990s was satellite positioning, including GPS (global positioning systems). GPS has revolutionised the way surveys are carried out and has become a standard item of equipment for surveyors. Unlike the systems used for general navigation purposes, the satellite positioning systems used by surveyors can provide positions to centimetric accuracies, and tied, in real time, to the National Grid. Indeed, satellite positioning has replaced the old network of benchmarks as the official means of connecting to the national levelling datum. The European Union, Russia and China are developing satellite positioning systems that will complement the existing American GPS system and generically these are known as GNSSs (global navigation satellite systems) (Figure 3).
The impact of these developments has been to make conventional surveying faster, more accurate and requiring fewer people, balanced against the need for continual investment in expensive equipment and the associated training. These developments have also enabled significant automation in areas such as machine control of construction plant and subsidence alert systems. With automated systems, the surveyor’s role changes from data collector to data-flow and system manager.
Data collection and storage
In parallel with this evolution in conventional survey instrumentation and methods, the last decade has seen a revolution in the collection and processing of point cloud data. The terrestrial laser scanner (TLS), for example, is a tripod-mounted instrument capable of collecting thousands of 3D points per second. The result is a dense, feature-rich point cloud representation of the object being surveyed from which accurate 3D models can be produced. Applications of terrestrial laser scanning include the recording of buildings, as-built surveys of oil refineries, 3D modelling for the film industry, and mapping of crime scenes. New areas of application are emerging constantly (Figure 4).
Vehicle-mounted systems that combine TLS, GPS and IMU (inertial measurement units) in a mobile mapping system have been developed and enable corridor surveys to be completed very rapidly. For example, the data collection for an as-built survey of 50km of new motorway was recently completed in Ireland in one day using mobile mapping. Other disciplines where 3D point cloud data are now being collected include hydrography, manufacturing and medicine using, respectively, multibeam echo sounders, laser-based hand scanners and MRI scanners. In all cases the skills of the geomatics professional are required to reliably process and manage the enormous data files that are produced (Figure 5).
Moving above ground, the development of high-resolution digital aerial cameras has ensured that photogrammetry (aerial mapping) remains the standard method for large-scale mapping. Meanwhile, fixed-wing or helicopter-mounted airborne laser scanning systems have been introduced that very rapidly collect the data from which accurate 3D models of the Earth’s surface can be created. In addition to contouring, these models are used for flood mapping, noise mapping and city modelling (Figure 6).
Space-borne sensors provide high resolution imagery of the earth’s surface. This imagery is processed by geomatics professionals and is used to study many aspects of our planet, including the dynamic changes caused by both natural processes and human practices (Figure 7).
In conclusion, it can be seen that the data collection technologies used in geomatics have changed out of all recognition in the last 25 years. The discipline employs cutting-edge technology and the areas of application extend far beyond the traditional role of mapping. While the adoption of these new technologies presents a range of challenges, they will provide exciting new prospects in the coming years. The skills that will set the surveyor apart are knowing how to use the tools productively, the potential errors and limitations in their operation, and what specific data to collect to create the required deliverables.
Dr Eugene McGovern FSCSI FRICSI
Eugene is a lecturer at the Department
of Spatial Information Sciences, Dublin Institute of Technology.