Measuring Vertical Distances

These flashcards cover key vocabulary and concepts from the notes on measuring vertical distances.

Line of Sight

A straight line from the eyepiece through the crosshairs through the optical center of the objective lens to a point on an object.

Spirit Level

An instrument consisting of a telescope and a sensitive spirit bubble vial used to establish a horizontal line of sight.

Parallax

The apparent movement of crosshairs across an image when the viewer's eye position changes, requiring elimination for proper focus.

Automatic Level

A self-leveling instrument that uses gravity to maintain a horizontal line of sight and does not have a tubular spirit vial.

Datum

A theoretical reference plane to which all other elevations are referenced.

Elevation

The vertical distance of a point above or below a given reference surface.

Benchmark

A permanent point of known elevation set with a high degree of accuracy.

Turning Point

A temporary reference point established by a surveyor and determined by differential leveling.

Differential Leveling

The operation of reading a vertical rod held alternately between two nearby points to determine the vertical distance between them.

Profile Leveling

The process of determining elevations of a series of points on the ground at uniform intervals along a centerline.

Average End Area Formula

A method for computing the volume of cut or fill that utilizes two adjacent cross-sections. The formula is \frac{(A1 + A2) \times L}{2} where A1 and A2 are the areas of two adjacent cross-sections, and L is the length between them.

Three Wire Leveling

A technique using three readings to the nearest .000’ to increase precision and help avoid errors.

Interior Angle

An angle measured on the inside of a closed traverse or polygon, typically between adjacent lines of the survey.

Exterior Angle

An angle defined as 360 - \text{Interior Angle}, typically measured on the outside of a closed traverse. It is often used for error checking in surveying.

Back Direction (Back Bearing)

The direction of a line observed from its terminal point back to its initial point. It is typically calculated as the forward direction plus or minus 180^{\circ}.

Forward Direction (Forward Bearing)

The direction of a line observed from its initial point to its terminal point.

Digital Level

An advanced self-leveling instrument that automatically reads a special bar-coded leveling rod and displays, stores, and performs calculations on the observed height.

Bulls-eye Spirit Vial

A circular spirit bubble vial used to establish approximate horizontal or vertical conditions. It indicates level when the bubble is centered within the circle.

Tubular Spirit Vial

A cylindrical spirit bubble vial, typically more sensitive than a bulls-eye vial, used for precise leveling in instruments like transits or dumpy levels. The bubble moves along a graduated tube.

Back Sight / Plus Sight

A rod reading taken on a point of known elevation (like a Benchmark) or a Turning Point, used to determine the Height of Instrument (HI). It is added to the known elevation.

Foresight / Minus Sight

A rod reading taken on a point whose elevation is to be determined. It is subtracted from the Height of Instrument (HI) to find the elevation of the point.

Height of Instrument 

The elevation of the line of sight of a leveling instrument. It is calculated as known elevation + Back Sight.

Basic Cycle of Differential Leveling

1. Set up level. 2. Take a Back Sight (+\text{S}) on a known elevation (BM or TP). 3. Calculate Height of Instrument (HI) = Known Elevation + BS. 4. Take a Foresight (-\text{S}) on an unknown elevation (TP or desired point). 5. Calculate Unknown Elevation = HI - FS.

Arithmetic Check

A method to verify leveling calculations: The sum of all Back Sights (BS) minus the sum of all Foresights (FS) should equal the difference between the End Elevation and the Beginning Elevation. (\Sigma BS) - (\Sigma FS) = \text{Last Elevation} - \text{First Elevation}

Least Count

The smallest measurement that can be made accurately with a particular measuring instrument. It represents the precision of an instrument.

Vernier Scale

A secondary scale, often sliding, used in conjunction with a main scale to increase the precision of a reading, allowing measurements to a fraction of the smallest division on the main scale.

Least Count of the Vernier

The difference between one smallest division on the main scale and one division on the vernier scale, which determines the precision achievable with the vernier system.

Vernier Index

The zero mark on the vernier scale, which is used to read the main scale value. The alignment of the vernier index with a main scale mark determines the primary reading.

Profile View

A longitudinal section view of the ground or an object along a specific line (e.g., a centerline), showing the vertical elevations along that line.

Cross-section View

A transverse section view of the ground or an object perpendicular to a centerline, showing the vertical elevations and horizontal distances at a specific station.

Full Station

A point along a survey line at an even multiple of the basic stationing interval (e.g., 1+00, 2+00, etc., for a 100 ft interval).

Plus Station

A point along a survey line located between two full stations, designated by the full station number followed by a plus sign and the additional distance (e.g., 1+50 for 150 ft beyond the starting point of station 1+00).

Waving the Rod

A technique used in leveling where the rod person gently rocks the leveling rod slightly towards and away from the instrument. This ensures the rod is vertical when the lowest reading is taken, which is usually the correct reading, as the line of sight intersects the rod's true vertical position.

Mass Haul Diagram

A graphical representation used in earthwork calculations to analyze excavation and embankment quantities along a construction project, aiding in balancing cut and fill and minimizing hauling distances and costs.

Cut Earthwork

The volume of material that must be excavated from the ground to achieve a desired grade or finished surface.

Fill Earthwork

The volume of material that must be added to the ground to achieve a desired grade or finished surface.

Grade Point

A specific point where the existing ground elevation matches the proposed finished (design) grade elevation, indicating a transition between cut and fill areas.

Planimeter

A mechanical or electronic instrument used to measure the area of an irregular shape drawn on a plane surface, such as a map or engineering drawing, by tracing its perimeter.