Surveying is the art and science of taking field measurements on or near the surface of the Earth. Survey field measurements include horizontal and slope distances, vertical distances, and horizontal and vertical angles. In addition to measuring distances and angles, surveyors can measure position as given by the northing, easting, and elevation of a survey station by using satellite-positioning and remote-sensing techniques. In addition to taking measurements in the field, the surveyor can derive related distances and directions through geometric and trigonometric analysis.
Once a survey station has been located by angle and distance, or by positioning techniques, the surveyor then attaches to that survey station (in handwritten or electronic field notes) a suitable identifier or attribute that describes the nature of the survey station. Attribute data for a survey station can be expanded from a simple descriptive label to include a wide variety of related information that can be tagged specifically to that survey station.
Since the 1980s, the term geomatics has come into popular usage to describe the computerization and digitization of data collection, data processing, data analysis, and data output. Geomatics includes traditional surveying as its cornerstone, but it also reflects the now-broadened scope of measurement science and information technology. Figure 1 shows a computerized surveying data model. This illustration gives you a sense of the diversity of the integrated scientific activities now covered by the term geomatics.
|Figure 1: Geomatics data model, showing the collection, processing, analysis, design, and plotting of geodata.|
The vast majority of engineering and construction projects are so limited in geographic size that the surface of the Earth is considered to be a plane for all X (easterly) and Y (northerly) dimensions. Z dimensions (height) are referred to a datum, usually mean sea level. Surveys that ignore the curvature of the Earth for horizontal dimensions are called plane surveys. Surveys that cover a large geographic area—for example, state or provincial boundary surveys—must have corrections made to the field measurements so that these measurements reflect the curved (ellipsoidal) shape of the Earth. These surveys are called geodetic surveys. The Z dimensions (orthometric heights) in geodetic surveys are also referenced to a datum—usually mean sea level.
In the past, geodetic surveys were very precise surveys of great magnitude, for example, national boundaries and control networks. Modern surveys (data gathering, control, and layout) utilizing satellite-positioning systems are geodetic surveys based on the ellipsoidal shape of the Earth and referenced to the geodetic reference system (GRS80) ellipsoid. Such survey measurements must be translated mathematically from ellipsoidal coordinates and ellipsoidal heights to plane grid coordinates and to orthometric heights (referenced to mean sea level) before being used in leveling and other local surveying projects.
Engineering or construction surveys that span long distances (e.g., highways, railroads) are treated as plane surveys, with corrections for the Earth’s curvature being applied at regular intervals (e.g., at 1-mile intervals or at township boundaries). Engineering surveying is defined as those activities involved in the planning and execution of surveys for the location, design, construction, maintenance, and operation of civil and other engineered projects.* Such activities include the following:
1. Preparation of surveying and related mapping specifications.
2. Execution of photogrammetric and field surveys for the collection of required data including topographic and hydrographic data.
3. Calculation, reduction, and plotting (manual and computer-aided) of survey data for use in engineering design.
4. Design and provision of horizontal and vertical control survey networks.
5. Provision of line and grade and other layout work for construction and mining activities.
6. Execution and certification of quality control measurements during construction.
7. Monitoring of ground and structural stability, including alignment observations, settlement levels, and related reports and certifications.
8. Measurement of material and other quantities for inventory, economic assessment and cost accounting purposes.
9. Execution of as-built surveys and preparation of related maps, plans, and profiles upon completion of the project.
10. Analysis of errors and tolerances associated with the measurement, field layout, and mapping or other plots of survey measurements required in support of engineered projects.
Engineering surveying does not include surveys for the retracement of existing land ownership boundaries or the creation of new boundaries. These activities are reserved for licensed property surveyors—also known as land surveyors or cadastral surveyors.
*Definition adapted from the definition of engineering surveying as given by the American Society of Civil Engineers (ASCE) in their Journal of Surveying Engineering in 1987.