NCEES FS 1.A

Instrumentation (e.g., GNSS/GPS, levels, total stations, robotic total stations, scanners, UAS)

What is a total station?

An electronic surveying instrument that combines angle measurement, electronic distance measurement (EDM), and data collection.

What does EDM stand for?

Electronic Distance Measurement.

What does a total station directly measure?

Horizontal angles, vertical/zenith angles, and slope distances.

What is a robotic total station?

A total station that can automatically track a prism and be remotely operated, often allowing one-person surveying.

What is a level used for?

Determining differences in elevation between points.

What is the line of sight of a level?

The horizontal line through the telescope/crosshairs used to take rod readings.

What is a backsight (BS)?

A rod reading taken on a point of known elevation, usually to determine the height of instrument.

What is a foresight (FS)?

A rod reading taken on a point whose elevation is being determined, usually before moving the instrument.

What is a benchmark (BM)?

A relatively permanent point with a known elevation.

What is GNSS?

Global Navigation Satellite System; the general term for satellite positioning systems such as GPS.

What is GPS?

The United States satellite-based positioning system; GPS is one component of GNSS.

What does a GNSS receiver determine?

Position from satellite signals, commonly expressed as latitude, longitude, and height or converted coordinates.

What is a terrestrial laser scanner?

An instrument that rapidly measures large numbers of 3-D points using laser ranging.

What is a point cloud?

A large collection of 3-D coordinate points representing surfaces or objects measured by a scanner or similar system.

What does UAS stand for?

Unmanned Aircraft System.

How can UAS be used in surveying?

To collect aerial imagery or other remotely sensed data for mapping, topography, photogrammetry, and site documentation.

Instrument precision vs. accuracy

Precision is repeatability/consistency of measurements; accuracy is closeness to the true or accepted value.

Why is instrument calibration important?

It helps identify or reduce systematic errors and confirms the instrument is operating within required tolerances.

What does EDM measure?

The distance between the instrument and a target using electromagnetic energy.

What is the purpose of a prism with a total station?

It reflects the EDM signal back to the instrument so distance can be measured accurately.

What is reflectorless measurement?

A total station measures distance directly to a surface without using a prism.

What is a prism constant?

A correction value accounting for the physical offset of the prism’s reflecting surface.

Why must a total station be centered over a survey point?

Poor centering introduces error into measured directions, angles, and positions.

Why must an instrument be leveled?

To establish the proper reference orientation for accurate angle and position measurements.

What is parallax in a surveying telescope?

Apparent movement between the crosshairs and target when the observer moves their eye, caused by improper focusing.

How is parallax removed?

Properly focus the eyepiece on the crosshairs and then focus the telescope on the target.

Why is a stable tripod setup important?

Instrument movement or settlement can introduce errors into measurements.

What type of environment generally gives GNSS the best results?

An area with a clear, unobstructed view of the sky.

What can obstruct GNSS signals?

Buildings, trees, terrain, structures, and other objects between the receiver and satellites.

What is satellite geometry?

The arrangement of satellites relative to the GNSS receiver; better distribution generally produces better positioning.

What is DOP in GNSS?

Dilution of Precision; an indicator of how satellite geometry affects position quality. Lower DOP generally indicates better geometry.

What does scanner registration mean?

Combining multiple scanner setups or point clouds into one common coordinate system.

Why are multiple laser scanner setups often needed?

Objects can block the scanner’s line of sight and create areas with missing data.

What is a major advantage of laser scanning?

It can rapidly collect a very dense set of 3-D measurements.

What is a major consideration when using UAS for surveying?

Flight planning, positioning/control, sensor quality, processing, and verification all affect the final accuracy of the data.