Surveying Terms

blunder

a significant but avoidable mistake in a surveying measurement caused by human inattention or carelessness

field book

a small notebook used to record original data and sketches made at the time of measurement in the field

chord

a straight-line segment with its endpoints on the perimeter of a circle

avulsion

a sudden and very noticeable change in the location of a shoreline that does not relocate the riparian boundary line

construction survey

a survey performed to mark the position on the ground of building corners, road locations, and other newly designed facilities and structures to be built

electronic total station

a surveying instrument with a combined digital electronic theodolite, an electronic distance measuring device, and a built-in computer that can process and record measurement data

centesimal system

a system of angular measurement used in some countries, in which a complete rotation (full circle) is divided into 400 grades or grads

cut sheet

a table indicating depth of excavation or fill required to reach grade on a construction project

chaining

a term sometimes used to describe the field procedure of taping horizontal distances

direction theodolite

a theodolite that has only an upper motion with a single clamp and tangent screw, connecting the alidade to the leveling head

connecting traverse

a traverse that begins and ends at different points/lines of a known position/direction

equilateral triangle

a triangle that contains three sides of equal length

direct reading scale

a type of internal optical scale in a theodolite, read by looking through a small eye piece mounted adjacent to the telescope

Florida rod

a type of level rod consisting of only one section 10 ft long

Chicago rod

a type of level rod consisting of three sliding sections; when the sections are unextended, it is more compact and portable than a Philadelphia rod

degree of arc

a unit of angular measurement in which a complete rotation is equivalent to 360 degrees and a right angle equals 90 degrees

centi-centigrad

a unit of angular measurement, where 1 centigrad = 100 centi-centigrads

centigrad

a unit of angular measurement, where 1 grad = 100 centigrads

double vernier

a vernier with a complete set of divisions running both ways, right and left, from a common zero line or index; angles may be read either clockwise (right) or counterclockwise (left)

blue top

a wooden stake set in the ground so that the top (painted blue) of the stake is at the required elevation or grade of construction

chorobate

an ancient device used for leveling, from Roman times through the middle ages, which depended on the free surface of water in a trough to establish a line of sight

cubit

an ancient unit for distance measurement, equal to the length of a human forearm

exterior angle

an angle measured on the outside of a closed polygon

degree of curvature

an angle that describes the "sharpness" of a simple curve; sharp curves have higher degrees of curves than "flat" curves

dumpy level

an early type of level used in the U.S. that has the bubble tube attached directly to a relatively long telescope

electronic data collector

an electronic recording device that automatically collects, stores, and displays data acquired by electronic surveying instruments to which it is attached

average end-area formula

an equation for computing the volume of earthwork (cut or fill) between adjacent cross-sections of a highway or railway route

electronic distance measuring instrument

an instrument that quickly and accurately measures distances using a beam of electromagnetic waves

electronic level

an instrument that uses electronic digital image processing and a special bar-coded level rod to determine, record, and display elevations

diurnal variation

daily changes in magnetic declination

bearing

direction of a line expressed as the angle from the north or south end of the meridian, whichever is nearest, to the line

embankment

excavated soil placed and compacted in a different location for construction purposes; also called fill

back azimuth

forward azimuth plus/minus 180 degrees

batter boards

horizontal boards, each attached to two vertical posts, used during the construction layout of the corners of a building

borrow

in earthwork calculations, the volume of soil or rock that must be moved to a construction site from somewhere else

cut and fill

in earthwork, excavation and embankment sections along a transportation route that establish the route's vertical alignment

error of closure

in leveling circuits and control traverses, the error or difference between the observed final position and the "true" position

backsight

in leveling, the rod reading on a point of known elevation; also called a plus sight; generally, a sight on a preceding point

cross section

in route surveys, a relatively short profile view of the ground or pavement, drawn perpendicular to the route centerline

cosine

in trigonometry, a function of an angle equal to the ratio of the side adjacent to the angle to the hypotenuse of a right triangle

cosecant

in trigonometry, the reciprocal of the sine function

cotangent

in trigonometry, the reciprocal of the tangent function

bubble tape

on a level or theodolite, a glass container filled with liquid and shaped so that when the bubble is centered, the direction of the telescopic line of sight is horizontal

central angle

the angle between two radii of a circle, with the angle's vertex at the center of the circle

curb return

the circular arc formed by a curb at a street intersection

contour interval

the constant vertical distance represented between successive contour lines on a topographic map

error

the difference between a measured quantity and its "exact" or "true" value, not due to blunders

back direction

the direction opposite to which fieldwork is carried out

forced centering

the exchange of a target or reflecting prism with a theodolite on a tribrach, maintaining a leveled and centered position

elevation axis

the horizontal axis around which a transit's telescope rotates in a vertical plane

celestial sphere

the imaginary spherical shell formed by the sky

data reduction

the mathematical procedure of converting all distance and angle measurements of a traverse into station coordinates

earthwork

the movement of soil or rock from one location to another for construction, including excavation, embankment, and fill

encroachment

the process of using and gradually taking possession of land belonging to someone else

drawing scale

the ratio between the length of a line on a drawing/map and the actual distance that line represents in reality

course

the straight line between two traverse stations

circumference

the total length of the curved line that forms a circle

area

the two-dimensional space encompassed within the boundary of a closed figure

azimuth axis

the vertical axis of a transit, passing through the alidade spindle and the leveling head; also called the standing axis

course departure

the x-component of a traverse line in a rectangular coordinate system

course latitude

the y-component of a traverse line in a rectangular coordinate system

complimentary angles

two angles whose sum is equal to a right angle

cross hairs

two intersecting perpendicular lines seen through a telescopic eyepiece of a surveying instrument to establish a line of sight

public domain land

land owned by the U.S. federal government

quadrangle

the largest parcel of land subdivision in the U.S. Public Land Survey System, approximately 24 miles on a side, subdivided into 16 smaller tracts called townships

pace

the length of one natural footstep while walking a level line

hypotenuse

the long side, opposite the 90-degree angle, in a right triangle

leveling head

the lower part of a level, transit, or theodolite, or EDMI on which the leveling screws operate; also called the footplate

horizontal circle

the middle part of a transit, between the alidade and leveling head, graduated in degrees (of arc) and fractions of a degree

setback

the minimum required distance between a new building and the front or side property lines, per local building codes

significant figures

the number of sure or certain digits in a measurement, plus one estimated digit

surface relief

the overall "shape" of the land (e.g. hills or valleys), shown on a topographic map

zenith

the point on the celestial sphere vertically above a given point

point of reverse curve

the point where two reverse curves meet

normal position

the position of the transit telescope with the spirit bubble tube underneath the scope

slope staking

the procedure for giving line and grade for the construction of earthwork side slopes or locating the edges of roadway cuts and fills that exceed 3 ft (1 m) in depth

profile leveling

the process of determining the elevations of a series of points on the ground, at mostly uniform intervals along a continuous line or route

repeating an angle

the process of measuring an angle with a transit or theodolite more than once (an even number of times), with the telescope reversed half of the time, to increase precision, reduce the effect of systematic errors, and eliminate blunders

interpolation of contours

the progress of estimating intermediate ground elevation values between observed data points to sketch contour lines on a map

normal tension

the pull on the tape required so that systematic errors due to incorrect tension and sag should cancel each other when taping

superelevation

the raising or banking of the outer edge of a roadway pavement or railway transportation route to resist the effect of centrifugal forces along a curved path

slope

the rate of change in grade or elevation of a line; rise over run

index error

the reading observed on the vertical circle of a transit when the telescope bubble tube is centered

grade rod

the reading on a level rod that would be seen from the given instrument position if the bottom of the rod were placed at the required grade of construction

straight line

the shortest line joining two points

gradient

the slope of rate of change in grade or elevation of a line

magnetic declination

the true bearing of a pivoted, freely swinging magnetic needle (called a compass)

grade line

the vertical alignment or profile of the center-line of a roadway or other type of transportation route

grade

the vertical position or elevation of a point

leveling screws

three or four screws on the leveling head of a level, transit, or EDMI, used to level the instrument by rotating the screws

orient to the curve

to set a transit on a curve with the vernier set at the appropriate deflection angle to proceed setting forward points on the curve

right-angle trig

trigonometric functions and relationships among the sides and angles of a right triangle

plunge the scope

turning the transit telescope 180 degrees around the elevation axis, from normal position to reversed position

supplementary angles

two angles whose sum is equal to the sum of two right angles

stride

two paces or steps

stadia hairs

two short, horizontal cross hairs in the reticle of a telescope, equally spaced above and below the central horizontal cross hair

radial survey

useful in open terrain, the process of making several angle and distance measurements from a single point or station of known position

horizontal

a direction perpendicular to the vertical direction (i.e. at a right angle to the direction of gravity)

slope distance

a distance measured in a direction other than horizontal, which eventually will be reduced (converted) to a horizontal distance

profile

a drawing that shows a vertical cross section or "side view" of the ground surface or roadway pavement along a route survey

planimetric map

a drawing that shows the horizontal positions of natural and cultural features on the land (but does not show surface relief)

plat

a drawing that shows the metes and bounds of a parcel of land, along with any buildings, fences, adjoiners, and other features

order of accuracy

a federal standard level of accuracy for horizontal or vertical control surveys

witnessing a point

a field procedure for referencing or locating a control point with horizontal ties so that it can be relocated in the future

grid-method leveling

a field procedure used to determine the typography of a small, uncluttered, gently sloping parcel of land

sector

a figure formed by an arc of a circle and its subtended central angle

meridian

a fixed reference direction

trapezoid

a four-sided plane figure with only one pair of opposite sides parallel

vertical circle

a graduated metal disk on the alidade of a transit used to measure vertical angles

level rod

a graduated rod held vertically at a point to measure elevation

link

a historical American unit of distance; one link is 0.01 chain or 7.92 in.

rod

a historical American unit of distance; one rod equals 0.25 chain of 16.5 ft

horizontal tie

a horizontal distance measurement that is used to locate the position of natural and cultural features to be shown on a map

riparian boundary

a land boundary line (either high water mark or centerline of a stream) of property adjacent to a body of water

horizontal distance

a length measured along a level surface

vertical distance

a length measured along the direction of gravity

objective lens

a lens at the forward end of a telescope that forms an image of the sighted target within the telescopic tube

precise level rod

a level rod constructed in one solid section with an attached, graduated invar-steel strip, used for precise leveling surveys

target rod

a level rod with a movable target and vernier scale that can be set by the rodperson at a position indicated by the instrument person, and read with greater accuracy by the rodperson

vertical control datum

a level surface, line, or point used as a reference from which the elevations of other points are determined

level circuit

a leveling survey that ends on either the starting benchmark, or another known benchmark, to check for blunders and determine the error of closure and order of accuracy

radius

a line from the center of a circle to any point on the circle

offset line

a line located parallel to the actual construction line, but offset 1 to 2 m so as not to be disturbed

secular variation

a long-term change in magnetic declination

representative fraction

a map scale expressed as a ratio of map distance to actual distance, with the number 1 in the numerator of the ratio

isogonic chart

a map showing magnetic declination contour lines and secular variation contour lines

pythagorean theorem

a mathematical formula which states that in a right triangle, the square of the hypotenuse equals the sum of the squares of the other two sides

transit rule

a mathematical method of distributing errors and adjusting the coordinates of a traverse so that it "closes"

compass rule

a mathematical method of distributing errors and adjusting the coordinates of a traverse so that it "closes" on a known point

trapezoidal rule

a mathematical method used to approximate the area enclosed between a traverse line and an irregular natural boundary line

least squares method

a mathematical procedure for adjusting the coordinates of a traverse so that it "closes"

coordinate transformation

a mathematical procedure to convert survey station coordinates from one reference system to another, usually to an SPCS

closing a level circuit

a mathematical procedure to distribute the error of closure among the intermediate benchmarks and to adjust the circuit so that the final observed benchmark elevation matches correctly

optical micrometer

a measuring device used with modern precise tilting levels to improve precision

planimeter

a mechanical or electronic instrument used to trace perimeters of plane figures of any shape, thereby measuring areas on maps

principal meridian

a meridian unique to each State for reference of quadrangles, townships, and sections, in the U.S. Public Land Survey System

tape clamp handle

a metal device used for providing a firm grip on a steel tape at any intermediate point without causing damage to the tape or injury to the surveyor from the steel edge

metes and bounds

a method for fully identifying and describing a parcel of land, including boundary line distances, directions, and adjoiners

plane surveying

a method of surveying measurement and computation methods that neglects the curvature of the Earth's surface

trigonometric leveling

a method used to determine the difference in elevation between two points indirectly by measuring a vertical or zenith angle and the slope distance between the two points, and using trig.

tilting level

a modern level equipped with an attached (or internal) parallel plate micrometer, used for precise leveling surveys

steel tape

a narrow ribbon of steel, typically 100 ft (or 30 m long), stored and carried on an open-reel case, graduated throughout its entire length in feet, tenths, and hundredths of a foot (or in meters and millimeters), used to measure horizontal (and slope) distances

rod reading

a number observed through a level where the level rod appears to be intersected by the horizontal cross hair of the telescope

sexagesimal system

a number system based on the number 60 in which a complete rotation (full circle) is divided into 360 degrees of arc

polar coordinates

a pair of numbers (r, A) that describe the location of a point at a distance r from the origin and at an angle A from the x-axis

rectangular coordinates

a pair of numbers (x,y) representing distances of a point from the origin (intersection point) of two perpendicular lines (axes) serving to describe the location of the point

stereopair

a pair of overlapping aerial photographs for viewing a 3-D image of the ground

rectangle

a parallelogram with four right angles

plane

a perfectly flat 2-D surface

point of beginning

a permanent marker on the boundary of a parcel of land that is used to start a metes and bounds description of the property

unit pace

a person's average pace length expressed as ft/pace or m/pace

gravity

a physical property of mass, manifested by a force of attraction directed toward the center of the Earth (i.e. vertical direction)

compass

a pivoted, freely swinging magnetic needle that rotates to align itself with the Earth's magnetic field

protractor

a plastic circular or semicircular device with graduations in degrees used to measure or draw angles on a drawing

reconnaissance survey

a preliminary survey conducted to get approximate or rough data regarding a tract of land

site plan

a special-purpose topographic map that shows all buildings, roads, and other facilities to be constructed on a parcel of land

tension handle

a spring-balance and handle attached to the forward end of a steel tape to indicate whether the correct tension (pull) is applied to the tape

stationing

a standard system for clearly identifying marks set on a line of measured distances; the marks are called stations

invar

a steel alloy relatively insensitive to temperature changes, used in some steel tapes and leveling rods for increased precision

lovar

a steel alloy relatively insensitive to temperature changes, used in some steel tapes and leveling rods for increased precision

cut tape

a steel tape marked every foot, with only the first and last foot intervals graduated in tenths and hundredths of a foot

line of sight

a straight line observed through a telescopic eyepiece, defined by the cross hairs and the optical center of the objective lens

diameter

a straight line that passes through the center of a circle and has its two ends on the circle; the longest chord of a circle

tangent

a straight line that touches or meets a curve at only one point; also, a trigonometric function of an angle equal to the ratio of the opposite side to the adjacent side in a right triangle

forward tangent

a straight-line section of a road or railway alignment that follows a connecting curve with the back tangent

back tangent

a straight-line section of a roadway or railway alignment that precedes a connecting curve and subsequent forward tangent

route survey

a survey for the design and construction of relatively "long and narrow" engineering projects (e.g. roads, railways, and pipelines)

topographic survey

a survey performed to determine the "shape" of the land and the locations of all existing natural and cultural features (e.g. streams, lakes, and houses) depicted on a topographic map

property survey

a survey performed to establish the location of boundary lines and property corners on the ground

hydrographic survey

a survey performed to map the shorelines and water depths of a river, lake, or harbor

geodetic surveying

a surveying method that takes Earth's curvature into account in measurements and data reduction

global positioning system/global navigation satellite system

a system of orbiting satellites that continuously broadcast radio signals, used to determine the coordinates and elevation of any point on the Earth's surface

instrumental error

a systematic error due to an imperfection or maladjustment of the measuring instrument

spindle

a tapered metal cylinder on the alidade of a transit, also called the inner center, which fits into the hollow outer center of the leveling head and allows rotation around the azimuth axis

turning point

a temporary mark or point conveniently located to serve as an intermediate reference when running levels

high rod

a term describing the use of a level rod in its extended position when leveling over steeply sloping terrain

repeating thedolite

a theodolite with two independent upper and lower motions

tripod

a three-legged wooden or aluminum stand on which levels, transits, theodolites, total stations, and so on are securely mounted

triangle

a three-sided polygon

township

a tract of land in the U.S. Public Land Survey System about 6 miles on a side, further subdivided into 36 sections

transit

a traditional American-style optical surveying instrument used primarily to measure horizontal and vertical angles

loop traverse

a traverse that starts and ends at the same point or station, thus forming a polygon

isosceles triangle

a triangle that contains two sides of equal length

oblique triangle

a triangle that does not contain a right angle

right triangle

a triangle with one interior angle of 90°

micrometer scale

a type of internal optical scale in a theodolite, requiring use of a knob on the instrument for index centering to read an angle

San Francisco rod

a type of level rod consisting of three sliding sections; when the sections are unextended, it is more compact and portable than a Philadelphia rod

Philadelphia rod

a type of level rod consisting of two sliding sections; when the rod is fully extended, its front face reads continuously from 0 at the bottom to 12 ft at the top

direct elevation rod

a type of level rod graduated to provide direct elevation readings, facilitating topographic or construction surveys

grad

a unit of angular measurement in which a complete rotation is divided into 400 grads, and a right angle equals 100 grads

radian

a unit of angular measurement in which a complete rotation is equivalent to 2 pi radians (1 radian is equivalent to 57.3°)

section

a unit of land in the U.S. Public Land Survey System about 1 square mile in area; there are 36 sections in a township

zenith angle/zenith distance

a vertical angle measured using the zenith direction as a zero reference line

summit curve

a vertical curve in a route survey with a negative change in grade between the forward and back tangents

sag curve

a vertical curve in a route survey with a positive change in grade between the forward and back tangents

sag

a vertical distance between the horizontal and the midpoint of a steel tape held horizontally between two points on the ground

elevation

a vertical distance measured above or below a benchmark or reference surface (usually mean sea level)

vertical tie

a vertical distance measurement for determining the elevation of a point to be shown on a topographic map

vertical control survey

a very accurate survey performed to establish a large network of benchmarks on the ground from which other, less-accurate, surveying measurements are made in the future

horizontal control survey

a very accurate survey performed to establish a large network of fixed stations on the ground from which other less-accurate surveying measurements are made in the future

measuring wheel

a wheel mounted on a rod and attached to an odometer, used for rough distance measurement by rolling the wheel along the line to be measured

keel

a yellow lumber crayon used to make marks on paved surfaces

subtended angle

an arc subtends (forms) a central angle between two radii from the center of the circle to the ends of the arc

magnetic azimuth

an azimuth measured with reference to a magnetic meridian

true azimuth

an azimuth measured with reference to a true meridian

right of way

an easement that gives the right to pass across the land or use the land for other purposes (e.g. storm drain)

inertial positioning system

an electromechanical device, which can be used to determine coordinates of survey points

systematic error

an error caused by imperfections in the measuring equipment, by the method of measurement, or by certain natural conditions

inverse trig function

an expression relating an unknown angle to a known value of one of its trig functions

side shot

an extra measurement of distance and direction from a traverse station to another point that is not part of the traverse

radial shot/side shot

an extra measurement of distance and direction to a point in the vicinity of a control traverse station

magnetic meridian

an imaginary line parallel to the direction taken by a pivoted, freely swinging compass needle

true meridian

an imaginary line that passes through a point on the Earth's surface and the Earth's geographic north and south poles

linear interpolation

for drawing contour lines based on the assumption that the ground slopes uniformly between adjacent contour lines

relative accuracy

for horizontal distance measurement, the ratio of closure to the true distance

three-wire leveling

for precise leveling surveys, a procedure that makes use of the central and stadia cross hairs; the three readings are averaged

nonmetallic tape

tapes made of fiberglass, synthetic yarn, or cloth, for use when relatively low-accuracy distance measurements are required

second (of arc)

an angular distance equal to one-sixtieth (1/60) of a minute of arc

hectare

SI metric unit of area, one hectare equals 10,000 square meters

horizontal datum

a basis for horizontal control comprising the coordinates of a point and the direction of a baseline passing through the point

magnetic bearing

a bearing measured with reference to a magnetic meridian

true bearing

a bearing measured with reference to a true meridian

geometry

a branch of mathematics concerned with the properties of and relationships among lines, angles, surfaces, and solids

trigonometry (trig)

a branch of mathematics concerned with the relationships among the sides and angles of a triangle

standard

a cast metal frame on the alidade of a transit that supports the telescope and vertical circle, allowing rotation of the telescope around the elevation axis

Gunter's chain

a chain of 100 heavy wire links with a length of 66 ft, used to measure distances until the introduction of modern steel tapes

upper motion

a clamp and tangent screw that controls motion of the horizontal circle relative to the alidade of a theodolite

lower motion

a clamp and tangent screw that controls the motion of the horizontal circle relative to the leveling head of a theodolite

vertical motion

a clamp and tangent screw that controls the vertical angle of a transit or theodolite telescope

quadrilateral

a closed plane figure with four sides and four angles

polygon

a closed plane figure with three or more straight sides

theodolite

a compact instrument for measuring angles accurately, with internal micrometer scales for precise reading of the circles

reticule/reticle

a component of a modern telescopic sight that provides the cross hairs near the rear of the telescopic tube

horizontal alignment

a connected series of straight lines and curves projected onto a horizontal plane on a drawing, locating the center-line of a route

parabola

a curve used in the vertical alignment of a transportation route, providing a constant rate of change of slope between tangents

level surface

a curved surface to which the direction of gravity is normal, or perpendicular, at all points

mirror stereoscope

a device used to view a stereopair of aerial photographs in 3-D

mean sea level

a primary reference level or datum for measuring elevations of points on land, determined by averaging the hourly elevations of the sea over a long period of time; or the position the ocean would take if tides and currents were eliminated

index centering

a procedure followed when using a theodolite to read an observed angle with high precision, by manipulating a knob to center the circle degree graduation mark between the double index lines; also called coincidence setting

pacing

a procedure for approximate distance measurement involving counting paces (single steps) while walking along a line to be measured

stadia survey

a procedure for measuring direction, distance, and elevation in one operation, using only a transit and level rod, for mapping

reciprocal leveling

a procedure for running levels accurately over obstacles, where the backsight and foresight distances must be different, using two instrument setups

waving the rod

a procedure used to assure that the level rod is in the vertical direction when the rod reading is taken

running levels

a procedure used to determine the elevations of two or more widely separated points for vertical control or profile surveys

vertical alignment

a profile view of the final grade line of a transportation route

running description

a property survey description that gives the direction and length of each boundary line in sequence, starting at a POB

resurvey

a property survey performed to relocate the original boundary lines for previously described and monumented land parcels

trapezium

a quadrilateral in which no two sides are parallel

parallelogram

a quadrilateral with each pair of opposite sides parallel

target

a readily visible object with a clearly marked point for setting a line of sight that can be centered over a point in a tribrach on a tripod

square

a rectangle with four equal sides

state plane coordinate system

a rectangular coordinate grid with central meridian and origin unique to each State in the U.S. for horizontal control surveys

topographic map

a scale drawing (also called a topo map) showing surface relief and the locations of all natural and cultural features on the land

vertical curve

a segment of a parabola in a vertical plane, used to connect the forward and back tangents of a highway route

vernier scale

a short graduated scale mounted parallel to the main scale to be read, used to provide more precise readings of the main scale

simple curves

a single arc of a circle, the most common type of a horizontal curve used in route surveys

gun

a slang term for a transit, a theodolite, or a level mounted on a tripod

tangent screw

a slow-adjustment screw on surveying instruments, to provide fine control of the direction of the telescope by turning a knob

hand level

a small metal or plastic tube with a horizontal line across the open end, a small peephole in the front, a spirit bubble, and a prism to reflect the split view of the bubble onto the line of sight, used for rough elevation measurements, making vertical ties, etc.

plumb-bob

a small weight, freely suspended at the end of a string, used to establish the vertical direction over a point or survey station

optical plummet

a small, vertical telescopic sight in the spindle of a theodolite, used to set up the instrument directly over a point or station

prism

a solid made up of several plane faces

tape thermometer

a special thermometer, attached to a steel tape, to account for tape expansion or contraction when high accuracy is required

minute (of arc)

an angular distance equal to one-sixtieth (1/60) of a degree

reverse curve

an "S-shaped" curve comprised of two opposite simple curves in the horizontal alignment of a transportation route

prism pole

an adjustable height pole with attached bull's eye spirit level and reflecting prisms for electronic distance measurement

vertical photo

an aerial photograph taken with the optical axis of the camera aligned in the vertical direction

oblique photo

an aerial photograph taken with the optical axis of the camera unaligned with the vertical direction

libella

an ancient surveying instrument used to establish a level line, using a triangular A-frame and a plumb-bob line at the vertex

vertical angle

an angle between two lines of sight measure in a vertical plane at the point of observation

horizontal angle

an angle between two lines of sight measured in a plane that is horizontal at the point of observation

obtuse angle

an angle greater than 90 degrees

interior angle

an angle measured on the inside of a closed polygon

straight angle

an angle of 180° (or 200 grads, or pi radians)

right angle

an angle of 90° (or 100 grads, or pi/2 radians)

stereoplotter

an instrument that makes it possible both to observe a 3-D image of the ground by viewing overlapping aerial photographs and to plot contour lines on a topographic map

odometer

an instrument used for measuring distances by relating the number of turns of a wheel to the linear distance covered

rotating-beam laser

an instrument with an internal optical system that continuously rotates a laser beam, generating a flat reference surface

laser

an intense narrow beam of light, used in electronic distance measurement instruments and for establishing line and grade

traverse

an interconnected series of lines (courses) running between a series of points on the ground (stations) for horizontal control

parallel plate micrometer

an optical device built in or attached to a modern tilting level, allowing very precise vertical displacements to be measured

horizontal curve

arcs of circles or spirals that connect the straight-line sections (back and forward tangents) of the horizontal alignment of a road or highway route

riparian rights

certain privileges the owner of property adjacent to a body of water has with respect to the use of the water

local attraction

disturbance of the direction of a compass needle due to nearby magnetic materials or power lines

reliction

gradual receding of water in a lake or stream as the water body dries up, moving the riparian boundary and increasing the area of a parcel of land on the shore

precise leveling

high order of accuracy leveling for vertical control, requiring the use of special leveling instruments, rods, and field methods

level

horizontal; the instrument used to make leveling surveys

side slope

in a route cross section, the ratio of a horizontal distance to a corresponding unit of vertical distance for a cut or fill slope

instrument person

in a surveying crew, the person using the tripod-mounted level, transit, theodolite, or electronic total station

rodperson

in a surveying crew, the person who holds the leveling rod in a vertical direction over the surveyed points

plumb

in a vertical direction

optical compensator

in an automatic level, a pendulum type of device that uses the force of gravity to set and maintain a truly level line of sight

shooting in grade

in construction surveys, setting a grade mark wherever desired by holding a level rod at each point and raising or lowering the rod until the target is on the line of sight of the transit where the height of instrument is equal to the target setting

mass diagram

in earthwork calculations, a graphical technique used to balance cut-and-fill quantities along a proposed transportation route

shrinkage

in earthwork calculations, the decrease in volume of soil due to compaction in an embankment

spiral curve

in horizontal alignment, it provides a gradual change in curvature from a tangent to a curve or another tangent; useful for railway routes or highway exit ramps to avoid sudden changes in curve

foresight

in leveling, a rod reading on a point of unknown elevation; also called a minus sight; generally, a sight on a forward point

relief displacement

in photogrammetry, the difference in position of an object or point on a vertical photo compared with its true planimetric position

rod shot

in profile leveling, a series of foresights on the level rod held at stations along the profile line to determine ground elevations

public land survey system

in the U.S., a rectangular framework created for surveying and describing large land parcels, primarily in mid-western and far western states

sine

in trig., a function of an angle, equal to the ratio of the side opposite the angle to the hypotenuse of a right triangle

secant

in trig., the reciprocal of the cosine function

self-reading rod

level rods that can be read directly by the instrument person

perpendicular lines

lines intersecting to form a right angle

photogrammetry

making precise measurements of images on aerial photographs to determine the relative locations of points and objects on the ground

mensuration

measurement of distances, areas, and volumes

leveling

measurement of the elevations of a continuous series of points

inverse computations

surveying computations that result in the direction and length of a line, starting with the coordinates of the line's endpoints

parallax

occurs when the image of a level rod is not focused exactly on the plane of the cross hairs, causing the rod reading to vary as the observer's eye is moved up or down

telescope

on levels, transits, theodolites, and total stations to magnify an image and obtain a line of sight on a rod, point, or target

rotation of axes

one of the steps in coordinate transformation involving a rotation of the meridian of the reference coordinate system

translation of axes

one of the steps in coordinate transformation, involving a displacement of the origin of the reference coordinate system

level book

one of two field books maintained when running levels, kept by the instrument person

peg book

one of two field books maintained when running levels, kept by the rodperson

line and grade

placing stakes or other reference marks in the field to establish the location, direction, and elevation of proposed construction

radial stakeout

radial survey methods used for construction surveys

natural errors

random errors not due to instrumental or personal causes

excavation

removal of soil or rock from its natural location for the purpose of construction

grade staking

setting wooden stakes/marks at required elevations to serve as reference points for construction

refraction

slight bending of light (and a line of sight) in the atmosphere

full station

stations marked at intervals of exactly 100 ft

parallel lines

straight lines in the same plane, which do not meet or intersect, no matter how far they are prolonged

reversed position

the "plunged" or "transited" position of the transit telescope with the spirit bubble tube on top of the telescope

inscribed angle

the angle formed between two chords that meet at a point on a circle

geographic latitude

the angular distance, north or south from the Earth's equatorial plane, of a point on the Earth's surface

most probable value

the average value of a series of repeated measurements

tribrach

the base of a theodolite, with a special release mechanism that allows the instrument to be easily exchanged with a target or reflector without disturbing the leveled and centered position

perimeter

the border or boundary of a two-dimensional plane figure; also, the total length of the border

trilateration

the computation of rectangular coordinates of survey stations using only distance measurements and trigonometry

reflecting prism

the corner of a solid glass cube, used to reflect laser light back to an electronic distance measurement instrument

precision

the degree of refinement or perfection used in a measurement

triangulation

the determination of the positions of horizontal control stations covering large ares, relying primarily on angular measurement

forward direction

the direction in which field work is carried out

vertical

the direction of gravity (i.e. toward the center of the Earth)

subdivision

the division of a large tract of land into two or more smaller parcels for sale as separate building lots

invert elevation

the elevation of the bottom inside surface of a sewer pipe or storm drain, established in the design and layout of pipelines

height of instrument

the elevation or height of the horizontal line of sight through the telescope of a level, transit, or other surveying instrument

taping

the field procedure of measuring distances with steel tape

segment

the figure formed by a chord and an arc of a circle

point of vertical curve

the intersection of a back tangent and a vertical curve along the vertical alignment of a road or other transportation route

point of tangency

the intersection of a horizontal curve and a forward tangent along the alignment of a transportation route; also called curve to the tangent or end of curve

point of vertical tangency

the intersection of a vertical curve and a forward tangent along the vertical alignment of a transportation route

point of curvature

the intersection of the back tangent and a horizontal curve along the alignment of a transportation route; also called tangent to curve or beginning of curve

point of intersection

the intersection of the back tangent and the forward tangent in the horizontal alignment of a road or other transportation route

point of vertical intersection

the intersection of the back tangent and the forward tangent in the vertical alignment of a road or other transportation route

vertex

the intersection of two sides of a plane figure; high point of a triangle

slope stakes

wooden stakes that mark the line where cut or fill side slopes intersect the original ground surface

closing the horizon

a procedure for checking horizontal angular measurements at a point by measuring the unused angle that completes the circle

double centering

a procedure used to accurately extend or prolong a straight line beyond a given endpoint using a transit or theodolite

compound curve

a roadway curve consisting of two simple curves with different radii, joined at a point of common tangency

declination arc

a scale on a compass that can be rotated to mark the magnetic declination so the compass reads true (or geographic) bearings

benchmark

a secure and permanent point of known elevation, usually above sea level, used to establish elevations of other points

cadastral survey

a boundary survey applied to the U.S. Public Lands Survey System, or to identification of property in political subdivisions

coordinate geometry

a branch of mathematics in which geometric shapes are defined and studied algebraically in a rectangular coordinate system

circle

a closed plane figure formed by a curved line, every point of which is equally distant from a single point inside the figure

coordinate method

a computational method used to calculate the enclosed area in a loop traverse when the coordinates of each station is known

double meridian distance method

a computational method used to calculate the enclosed area in a loop traverse with adjusted latitudes and departures

depression contour

a contour line that encloses low ground with no drainage path

azimuth

a direction of a line expressed as the clockwise angle between the line and a given reference direction or meridian

engineer's scale/equivalence scale

a drawing scale in the form of an equivalence, where a length of one unit on the scale is equivalent to a specified number of other units in the field

cross-section leveling

a field procedure for obtaining relatively short profile views of the ground, perpendicular to the main route centerline

breaking tape

a field procedure to measure horizontal distances over steeply sloping terrain, using one or more intermediate marks on line

bucking in

a field procedure used to establish a point on a line between two given marks when the points are not inter-visible due to a hill and when it is impossible to set up over either of the marks

chain

a historical American unit of distance measurement; one chain equals 66 feet

deflection angle

a horizontal angle between the extension of a back or preceding line and the succeeding or next line forward

easement

a legal right to use someone else's land for a specific purpose

focusing lens

a lens that can be moved back and forth inside a telescopic tube to focus the image on the cross hairs

eyepiece

a lens that magnifies the cross hairs in a telescope and that must be focused on them according to observer's eyesight

automatic level

a level with an internal optical compensator that automatically takes over (using gravity's effect), after approximate leveling of the instrument, to set and maintain a truly level line of sight

contour line

a line on a topographic map showing points of equal elevation

bisector

a line that divides another line (or angle) into two equal parts

closing a traverse

a mathematical procedure to eliminate geometric inconsistency in traverse station coordinates due to an error of closure

barometric leveling

a method of determining land elevations in preliminary surveys using barometers to measure air pressure

decimal system

a number system based on the number ten