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- Triangulation consists of the measurement of the angles of a
series of overlapping triangles, polygons, or quadrilaterals.
- Trilateration determines a position of a point on the Earth's
surface with respect to two other points by measuring the distances

between all three points.
- Transverse survey is a sequence of instrument setups that start at
a known location and end at another known location, with the

intermediate setups being at points with unknown coordinates.
- In the free station method of measurement, coordinates are
computed for an instrument setup at an unknown location.
2. Vertical control may be established by many different

methods (including trigonometric and barometric leveling, and GPS).
The primary vertical control network is established using differential
leveling.

- Leveling permits the precise measurement of elevational
differences between known and unknown points on the Earth’s
surface.

- GPS is a constellation of Global Positioning System (GPS)
satellites orbiting the Earth. It is used to determine the horizontal and
vertical position(s) of GPS ground receivers.

Few surveying techniques and methods are used for horizontal
and vertical measurement. The most common techniques employed
include:
- Theodolite or transit surveys is used for measuring angles and

distances and for cacluating positions and heights.
- Inertial systems - a gyro stabilized platform that starts at a point
of known position and elevation.

- LIDAR (Light Detection and Ranging) are lasers on board an
aircraft that “scan” the ground surface to calculate distances.
- Photogrammetry or Remote Sensing uses stereographic pairs of
photographs to indirectly measure objects on the ground and then

calculate point coordinates.

Task 3. Answer the questions to the text.

1. What is surveying?
2. What types of measurements can be undertaken in surveying
methods?
3. What instruments are used in distance and direction

measuring?

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