ENEV 281 – Chapter 6 - Surveying, Mapping, and Information Systems

This set of vocabulary flashcards covers key concepts, formulas, and terminology from Chapter 6, including horizontal and vertical angle measurement, azimuths and bearings, magnetic declination, and the errors associated with survey instruments.

Vertical Angle

An angle between two lines of sight measured in a plane that is vertical at the point of observation.

Zenith Angle

An angle measured from a vertical line of sight pointing directly upward toward the zenith; the scale reads exactly zero in this position.

Interior Angle

A horizontal angle measured on the inside of a closed polygon.

Exterior Angle

A horizontal angle measured outside of a closed polygon.

Angle to the Right

A horizontal angle measured in a clockwise direction, looking from above down on the instrument, from the rear to the forward station.

Angle to the Left

A horizontal angle measured in a counter-clockwise direction from the rear to the forward point.

Backsight

The act of pointing the instrument toward the rear station.

Foresight

The act of pointing the instrument toward the forward station.

Deflection Angle

A horizontal angle between the extension of a back or preceding line and the succeeding line forward, which is always less than $180^{\circ}$.

Azimuth

The clockwise horizontal angle between a line and a given reference direction or meridian, usually North.

Bearing

The angle from the North (N) or South (S) end of the meridian, whichever is nearest, to a line, always accompanied by two letters indicating the quadrant.

Back Azimuth

The direction of a line determined by adding or subtracting $180^{\circ}$ to the forward azimuth.

Back Bearing

The direction of a line determined by reversing the quadrant letters of the forward bearing while keeping the numerical value the same.

True Meridian

An imaginary line at a point that passes through the geographic North and South poles of the Earth; its direction is fixed at any given point.

Magnetic Meridian

The direction taken by a freely swinging magnetic needle suspended in a compass.

Magnetic Declination

The true geographic bearing of a freely suspended magnetic needle representing the angle between the true meridian and the magnetic meridian.

Theodolite

An instrument used to measure angles with precision varying from $\pm 0.1\,\text{second}$ to $\pm 0.1\,\text{minute}$.

Optical Plummet

A tool used to adjust the position of the instrument to ensure it is centered exactly over a station point.

Plate Spirit Bubble Tube

A component used for precise leveling of the instrument by aligning it with axes and centering the bubble using screws.

Closing the Horizon

Measuring the unused angle that completes a circle at a station to check that the total sum of angles equals exactly $360^{\circ}$.

Sum of Interior Angles

The total sum of all internal angles in a closed polygon, calculated using the formula $180(n-2)^{\circ}$ where $n$ is the number of sides.

Sum of Exterior Angles

The total sum of all external angles in a closed polygon, calculated using the formula $180(n+2)^{\circ}$ where $n$ is the number of sides.

Regina Magnetic Declination (June 2024)

The measured value of $+8^{\circ}\,25'$, which is considered positive (East).

Parallax

A personal error caused by incorrect focusing.

Accuracy Ratio for $1'$

The consistency ratio defined as $1:3440$ for an angular error of one minute.

Accuracy Ratio for $1''$

The consistency ratio defined as $1:206,000$ for an angular error of one second.

Instrumental Errors

Systematic errors such as the line of sight not being perpendicular to the horizontal axis or the optical plummet not being aligned with the vertical axis.

Natural Errors

Errors caused by environmental factors like atmospheric conditions, wind vibrations, or heat waves.

Tribrach

A component of a traverse set used together with an adapter and a sighting target.

Angle-Distance Relationships

The practice of balancing angular and linear measurements so that the true location of a point lies in the center of an approximate square with side dimension $2C$.