Surveying and Geomatics Flashcards

Introduction and History of Surveying

Definitions

• Surveying, also known as geomatics, is the science, art, and technology of determining the relative positions of points above, on, or beneath the Earth's surface, or of establishing such points.

• It involves:

  • Measuring and collecting information about the physical Earth and environment.

  • Processing that information.

  • Disseminating resulting products to a wide range of clients.

Applications

• Earliest application: measuring and marking boundaries of property ownership.

• Land value differences exist (e.g., New York vs. Texas, California vs. Texas).

• Reasons for measuring and monitoring the environment:

  • Population expansion.

  • Land value appreciation.

  • Diminishing natural resources.

  • Human activities.

• Growing demand and need for:

  • Variety of maps.

  • Spatially related types of information.

  • Establishing accurate line and grade for construction operations.

Abilities of a Surveyor

A surveyor is a professional with the academic qualifications and technical expertise to:

• Determine, measure, and represent the land, three-dimensional objects, point-fields, and trajectories.

• Assemble and interpret land and geographically related information.

• Use that information for the planning and efficient administration of the land, the sea, and any structures thereon.

• Conduct research into the above practices and develop them.

Surveying and Geomatics

• The manner and scope of practice in surveying have changed dramatically.

• Historically, surveyors used ground-based methods like transit and tapes.

• Modern surveyors use:

  • Electronic instruments for automatically measuring distances and angles (e.g., Total station).

  • Satellite technologies for precise position of spaced points (e.g., GPS (Global Positioning System), GNSS (Global Navigation Satellite System)).

  • Modern aerial digital imaging and laser scanning systems (e.g., LiDAR).

  • Computer systems to process measured data.

• Evolution of geographic information systems (GIS).

• Emerging demands for high-quality data collection and processing.

• The term 'Geomatics' evolved to reflect expanded and changing roles.

History of Surveying

• Surveying science began in Egypt.

• Sesostris (c. 1400 B.C.) divided the land of Egypt into plots for taxation.

• Annual Nile floods swept away portions of these plots.

• Surveyors (rope-stretchers) were appointed to replace boundaries.

• Early Greek thinkers developed the science of geometry as a consequence.

• Heron applied science to surveying around 120 B.C.

  • 'The Dioptra' includes methods of surveying a field, drawing plans, and related calculations.

  • Diopter: one of the first pieces of surveying equipment recorded to measure angles or altitudes.

• Frontinus, a Roman military engineer, wrote about surveying practices in ancient Rome.

  • Groma helped precise surveying of straight lines and right angles.

Early Understanding of Earth's Shape

• Early civilizations assumed the Earth to be a flat surface.

• Realization of the planet being curved:

  • Earth's circular shadow on the moon during lunar eclipses.

  • Watching ships gradually disappear as they sailed toward the horizon.

• Eratosthenes computed Earth's dimensions in 200 B.C.

  • Used Syene and Alexandria, two cities in Egypt.

  • Assumed Sun's rays are parallel.

  • At the summer solstice, the Sun's rays fall vertically at noon at Syene.

  • Determined the angle between the two cities from the shadow cast at Alexandria from a known length of a vertical object.

  • Arc length calculated by multiplying # of caravan days between the two cities by average daily distance traveled.

  • Approximated Earth's circumference as approximately 25000 miles (within 0.5% to 17% range of accepted value by modern astronomers).

Advancements in the 18th and 19th Centuries

• The art of surveying advanced more rapidly.

• England and France made extensive surveys for maps and national boundaries.

• Accurate triangulation requirement emerged Geodetic surveying.

• Congress established the U.S. Coast Survey (National Geodetic Survey of the U.S. Department of Commerce) in 1807.

  • Earlier task was to perform hydrographic surveys and prepare nautical charts.

  • Later tasks expanded to establish reference monuments of precisely known positions throughout the country.

• Surveying played an important role in the nation's defense activities, and military operations lead to the improvement of surveying instruments and methods.

Modern Surveying Equipment

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• Traditional surveying equipment was utilized until the 1960s to 1970s

  • Transit, theodolite, dumpy level, and steel tape were common tools.

• New high-tech instruments replaced traditional tools:

  • Total stations: automatically measure and record horizontal and vertical distances and angles.

  • GNSS/GPS: provides precise location information.

  • Laser scanning instruments: computes dense grids of coordinated points.

  • digital photogrammetric restitution instruments (softcopy plotter): Process and obtain spatial information from digital images captured by aerial cameras and remote sensing instruments.

Types of Surveying

• Two general classifications of surveys:

  • Geodetic Surveying

    • The curved surface of the earth is considered.

    • Usually more accurate than plane surveying.

  • Plane surveying

    • The reference base for fieldwork and computation is assumed to be a flat horizontal surface.

    • Except in surveys covering extensive areas, the Earth’s surface can be approximated as a plane, thus simplifying computations and techniques.

    • Therefore, plane surveying techniques are considered in this course and many real-life projects.

Importance of Surveying

• The results of today’s surveys are used to:

  • Map the earth above and below sea level.

  • Prepare navigational charts for use in the air, on land, and at sea.

  • Establish property boundaries of private and public lands.

  • Develop data banks of land-use and natural resource information that aid in managing our environment.

  • Determine facts on the size, shape, gravity, and magnetic fields of the earth

  • Prepare charts of our moon and planets.

  • Plan, construct, and maintain structures/facilities (highways, railroads, rapid-transit systems, buildings, bridges, missile ranges, launching sites, tracking stations, tunnels, canals, irrigation ditches, dams, drainage works, urban land subdivisions, water supply and sewage systems, pipelines, and mine shafts).

• Surveying is important in many related tasks (agronomy, archeology, astronomy, forestry, geography, geology, geophysics, landscape architecture, meteorology, paleontology, and seismology, but particularly in military and civil engineering).

Considerations for Surveyors and Engineers

• Surveyors and Engineers must know:

  • When to work to hundredths of a foot instead of to tenths or thousandths or nearest foot.

  • What precision is necessary to justify the computation to the desired number of decimal places (obtained with experience).

  • Except for some topographic work, only exceedingly small errors can be tolerated in surveying, and there is no factor of safety (unlike other engineering designs).

  • Taking detailed notes on-site is important for further calculation.

Suggested Reading

• 1.6 Specialized types of surveying

• 1.7 Surveying safety

• 1.8 Land and geographic information systems

• 1.9 Federal surveying and mapping agencies

• Section 1.10 to 1.13