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MESLEKİ TERMİNOLOJİ I
Doç. Dr. Atınç PIRTI
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GLOSSARY
Abutment. That part of a bridge substructure (that directly receives thrust or pressure) which supports the
end of the superstructure and retains the approach fill.
Adjustment. The determination and application of corrections to observations, for the purpose of reducing
errors or removing internal consistencies in derived results.
Accuracy. The conformity of a measurement to the "true" value or to a standard.
Accuracy ratio. The error in a measurement divided by the overall value of the measurement, expressed
as a fraction with a numerator of 1 and a denominator rounded to the closest 100 units; e.g., an error of 1
m in 3000 m would result in an accuracy ratio of 1:3000.
Alignment. The location of the horizontal reference line of a survey or a facility. The location of points with
reference to a straight line or to a system of straight lines.
Automated survey. The use of electronic surveying instruments or electronic data collectors to gather
surveying data with a minimum of manual input, and with the ability to electronically transfer the data to a
computer for further processing.
Astronomic azimuth. The angle measured to the right from the vertical plane through the celestial pole
and the observer to the vertical plane through observer and the observed object.
Automatic level. A surveyor's level which has the line of sight automatically maintained in the horizontal
plane once the instrument is coarsely leveled.
Azimuth. The horizontal angle to a line of sight, measured clockwise from a north meridian.
Backsight. (1) In leveling, a sight taken to a point of known elevation, thus permitting the surveyor to
compute the elevation of the instrument. (2) In traverse work, a sight taken to a previously located point to
establish a reference for angular measurement.
Baseline. A line of reference for surveying work.
Bearing. Direction of a line given by the acute angle from a meridian and accompanied by a cardinal
compass direction.
Bench mark A fixed, solid reference point with a precisely determined, published elevation.
Benchmark Something that serves as a standard by which other things may be measured or judged.
Blunder. Incorrectly measured or recorded data by an observer or recorder resulting from carelessness or
confusion. A mistake.
Cadastral map. A map showing the boundaries of subdivisions of land.
Cadastral survey. A survey relating to land boundaries and subdivisions of land.
Calibration. The act or process of determining certain specific measurements in a device by comparison
with a standard, for use in correcting or compensating for errors. Determining the systematic errors in a
measuring device by comparing its measurements with the measurements of a device that is considered
correct.
Cap. See survey cap.
Cartesian coordinates. A coordinate system in which locations of points in space are expressed by
reference to three mutually perpendicular planes.
Central meridian. A reference meridian in the center of the zone covered by the plane coordinate grid.
Chi-square test. A statistical test on the standard error of unit weight.
Chord. A straight line joining any two points on an arc.
Circular curve. A curve with a constant radius.
Clinometer. A hand-held instrument that combines a vertical circle, a spirit level and a sighting device for
coarse but rapid measurement of vertical angles.
Closed traverse. A survey traverse which starts and ends on known control stations.
Closure. Agreement between computed and known parts of a control network.
Combination factor. A factor used to convert ground distances to grid distances on a map or projection
system. The product of the scale factor and either the elevation factor or sea level factor.
Compass. An instrument that indicates the direction of north and the directions of other points with
respect to north.
Compass rule adjustment. A method of balancing a traverse survey. Corrections corresponding to the
closing errors in latitude and departure are distributed according to the proportion: length of line to total
length of traverse.
Compilation. Selection, assembly and graphic presentation of all relevant information required for the
preparation of a map or chart.
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Compound curve. Two or more circular arcs turning in the same direction having common tangent points
and different radii.
Constraint. External limitations imposed upon the adjustable quantities (observations and coordinates) in
a network adjustment.
Construction survey. Establishment of points and elevations for building of engineering projects.
Contour interval. Difference in elevation between two adjacent contour lines.
Contour line. A line on a map joining points of equal elevation.
Control point. A monumented point for which coordinates are known.
Control survey. A survey to establish reference points, elevations, or lines to be used as the starting
point for subsequent surveys.
Conventional survey. As distinguished from GPS observations. A loose generic term embracing the use
of theodolites, EDMs, chains, levels, etc.
Convergence. See mapping angle.
Convergence of meridians. The angular drawing together of geographic meridians in passing from the
equator to the poles.
Conversion factor. A quantity by which the numerical value in one system of units must be multiplied to
arrive at the numerical value in another system of units.
Coordinate conversion. A coordinate transformation when both coordinate systems are based on the
same mathematical reference surface.
Coordinates of a point. The distances measured north and east of a reference point having zero
coordinates.
Coordinate System. Any two or three-dimensional reference frame which can be used to locate objects
in space.
Coordinate transformation. Changing the coordinate values of a point from one system to those of
another system.
Coordinated Universal Time (UTC). Time counted from 0 hours at midnight at 0 degrees longitude
(Greenwhich). Central Standard Time (Wisconsin) is UTC minus 6 hours and Central Daylight Savings
Time is UTC minus 5 hours.
Corner. A point determined by the surveying process.
Cross section. A profile of the existing surface taken at right angles to a reference line.
Curvature correction. The correction applied to account for the divergence of the surface of the Earth
from a horizontal plane.
Data collector. An electronic field book designed to store field data, both measured and descriptive which
also may have the ability to communicate with electronic surveying instruments.
Datum. An assumed or fixed horizontal or vertical reference surface.
Deck. Floor of a bridge or structure.
Deflection angle. A horizontal angle measured from the prolongation of the preceding line to the following
line. Deflection angles to the right are positive; those to the left are negative.
Degrees of freedom. The number of observations which are in excess of the number actually needed to
calculate the unknowns.
Delta X, delta Y, delta Z. Coordinate differences expressed in the coordinate system for a pair of points.
Departure. The change in easterly displacement (Delta E) of a line.
Disk. See survey disk.
Differential Leveling. Determining the differences in elevation between points using a surveyor's level.
Eccentricity. Amount of deviation from center.
EDM. Electronic Distance Measurement.
EDMI. Electronic Distance Measuring Instrument.
Elevation. The vertical distance above or below a given datum.
Elevation factor. The factor used to convert ground horizontal distances to geodetic distances at ellipsoid
height of zero.
Ellipsoid. A mathematical best-fit representation of the Earth's surface. Formed by rotating an ellipse
about its minor axis.
Ellipsoid height (h). The elevation of a point above the reference ellipsoid for the horizontal datum,
currently NAD 83.
Engineering surveys. Preliminary and layout surveys used for the design and construction of facilities.
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Error. The difference between an observed or computed value of a quantity and the theoretical or defined
value of that quantity.
Error of Closure. The amount by which a quantity obtained by a series of related measurements differs
from the true or fixed value of the same quantity.
Error ellipse. A confidence region of a point’s accuracy represented by a ellipse. Represents an area
within which the probability of two-or (three)?-dimensional errors is a constant.
False easting, false northing. Arbitrary coordinates assigned to the origin of a mapping projection to
prevent the occurrence of negative coordinate values.
Fixed coordinates. Point coordinates which are not subject to adjustment.
Foot, International. Defined as exactly 0.3048 meter.
Foot, U.S. Survey. Defined as exactly 1200/3937 meter. The unit of linear measure in Wisconsin for
surveying.
Foresight. In leveling, a sight taken to a bench mark (BM) or turning point (TP) to obtain a check on a
leveling operation or to establish an elevation on a point. In a traverse, the foresight is a sight taken to a
point in order to establish a reference distance and direction.
Fully constrained. A network adjustment in which all points in the network which are part of a larger
control network are held fixed to their published coordinate values. Used to merge smaller with larger
control networks.
Geodetic azimuth. The clockwise angle measured usually from north between the mathematical
reference geodetic meridian and the observed line.
(Geodetic Azimuth = Grid Azimuth + Mapping Angle).
Geodetic control. Control points which take into account the size and shape of the earth.
Geodetic distance. The distance between two points on the reference ellipsoid. It differs from the ground
distance by a correction based on the elevation (or sea level) factor for the line.
Geodetic meridian. A line on a reference ellipsoid which has the same longitude at every point.
Geodetic Reference System 1980. A rotational ellipsoid having a semi major axis of 6,378,137 meters by
definition and a semi minor axis of 6,356,752.31414 meters by calculation. The reference ellipsoid for the
North American Datum of 1983.
Geographic coordinates. Latitude, longitude, and height above the reference ellipsoid.
Geoid. The average position of mean sea level. The equipotential surface in the gravity field of the Earth
which coincides with the undisturbed mean sea level extended continuously through the continents. The
direction of gravity is perpendicular to the geoid at every point.
Geoid height (N). The distance of the geoid above (positive) or below (negative) the mathematical
reference ellipsoid.
Global Positioning System. A three-dimensional positioning technique based on the reception and
analysis of NAVSTAR satellite signals.
GPS. See Global Positioning System.
Government lot. Sections made fractional by barriers, such as bodies of water. The lot number is the
legal description of that tract of land.
GRS 80. See Geodetic Reference System of 1980.
Grid azimuth. The clockwise angle measured usually from north on a projection grid between the central
meridian of a plane coordinate projection system and the observed line. Grid Azimuth = Geodetic Azimuth
- Mapping Angle
Grid distance. The distance between two points on a plane coordinate projection system. It differs from
the geodetic distance by a correction based on the scale factor for the line.
Grid north. The direction of the central meridian in a plane coordinate projection system.
Grid meridian. Meridians parallel to a central meridian on a coordinate grid.
Grid transformation. The conversion between geographic and map projection coordinates.
Ground distance. The horizontal distance between two points as measured on or near the surface of the
ground.
Hand level. A hand-held instrument used for approximate leveling.
Height of instrument (HI). Height of the optical axis of the instrument above the station (bench mark).
Commonly referred to as “the HI.”
Horizontal control. A network of stations of known geographic or grid coordinates referred to a common
horizontal datum, which control the horizontal positions of subsequent surveys.
Hydrographic survey. A survey which defines shoreline and depth of a body of water.
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Initial point. The point from which a survey is initiated. Also see point of beginning.
Inscription. Information on a survey disk identifying the agency supplying the survey disk (usually the
same agency physically setting the monument and usually the first agency to perform observations at the
survey station), the type of survey station, and a contact for more information about the station. When
survey disks were cast of brass, the inscription information was incorporated in the casting. Today survey
disks are normally formed (stamped) from a metal pellet and the inscription information is usually stamped
on the survey disk as part of the process of making the disk. Also see “stamping.”
Invert. The inside bottom of a pipe or culvert.
Invert elevation. The minimum flow elevation.
Lambert conformal projection. A conformal map projection in the shape of a cone on which all geodetic
meridians (lines of longitude) are represented by straight lines which meet in a common point outside the
map limits and parallels (lines of latitude) are represented by a series of arcs of circles having this
common point for the center of the arcs. Meridians and parallels intersect at right angles, and angles on
the Earth are correctly represented on this projection. The direction of the central meridian on the
projection establishes grid north.
Landowner. A person(s) who legally owns the land.
Laser level. A device which emits a horizontal laser beam for leveling operations.
Latitude (of a course). The change in northerly displacement (Delta N) of a line.
Latitude (geodetic). Angular distance measured north or south of the equator on a reference ellipsoid.
Least-squares adjustment. A method of adjusting observations by producing the smallest change to the
original field measurements. Simultaneously adjusts angular and linear measurements to make the sum of
the squares of the weighted residuals a minimum—hence the name.
Level line. (1) A straight line on a level surface (e.g., a beam of light perpendicular to the direction of
gravity at a single point); therefore, a curved line relative to the surface of the Earth. A level line is NOT a
line of constant elevation. (2) The route of a series of bench marks leveled during a leveling project.
Leveling. The surveying operation to measure the vertical distance between point(s) to determine the
elevation of the point(s).
Level of significance. An expression of probability. A one-sigma (standard) error is said to have a level of
significance of 68%. For one-dimensional errors, a 95% level of significance is expressed by 1.96 sigma,
and a 99% level of significance is expressed by 2.576 sigma.
Longitude (geodetic). An angular distance measured east or west from a reference meridian (usually
Greenwich, England) on a reference ellipsoid.
Lost corner. A PLSS corner whose position cannot be determined, beyond reasonable doubt, either from
traces of the original markers or from acceptable evidence or testimony that bears upon the original
position, and whose location can be restored only by reference to one or more interdependent corners.
Magnetic declination. The angle between the magnetic and geodetic meridian at any place, expressed in
degrees east or west to indicate the direction of magnetic north from true north.
Map projection. A rigorous mathematical expression of the curved surface of the ellipsoid on a
rectangular coordinate grid.
Mapping angle. The angle between grid north on a mapping projection and the meridian of longitude at a
given point. Also called the angle of convergence.
Mean sea level (MSL). The average height of the surface of the sea for all stages of the tide. Elevations
used to be commonly referenced to MSL. Since MSL is not a constant elevation at different locations it is
no longer used as a reference for elevations. See also National Geodetic Vertical Datum of 1929 and
North American Vertical Datum of 1988.
Meridian. A north-south reference line from which differences of longitude and azimuths are reckoned.
Metes and bounds survey. A method for describing boundaries of property by giving the bearing and
length of each successive line.
Minimally constrained. A network adjustment in which only enough constraints to define the coordinate
system are employed. Used to measure internal consistency in observations.
Monument (for geodetic survey). A permanent reference point for horizontal or vertical positioning.
Usually including an identifying name stamped on a bronze disk set in the top of a concrete post or drill
hole in a concrete structure.
Monument (for a boundary survey). A permanent reference point for horizontal positioning. Usually with
an identifying name stamped on it.
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National Geodetic Survey (NGS). The federal agency—under the National Ocean Service, National
Oceanic and Atmospheric Administration (NOAA), U.S. Department of Commerce—which is responsible
for establishing and maintaining the basic nationwide geodetic network.
National Geodetic Vertical Datum of 1929 (NGVD 29). Equipotential surface representing mean sea
level which is used for referencing orthometric heights.
NAVSTAR. NAVigation Satellite Timing And Ranging. A system of orbiting satellites used in navigation
and positioning. Commonly referred to as the Global Positioning System (GPS).
North American Datum of 1927 (NAD 27). Reference surface for horizontal positions. Adjustment
utilized the Clarke Spheroid of 1866 and held fixed the latitude and longitude of station Meades Ranch in
Kansas along with the azimuth to nearby station Waldo.
North American Datum of 1983 (NAD 83). Reference surface for horizontal positions. Adjustment
utilized the GRS 80 ellipsoid, centered at the mass center of the Earth, and held fixed the latitudes and
longitudes of numerous control stations.
North American Vertical Datum of 1988 (NAVD 88). Equipotential surface approximating the surface of
the geoid. Adjustment incorporated additional level lines to account for inconsistencies in NGVD 29.
Obliterated corner. A PLSS corner with no remaining traces of the monument or its accessories, but
whose location has been perpetuated, or a point which may be recovered beyond reasonable doubt by
the acts and testimony of the interested landowners, competent surveyors, other qualified local authorities,
or witnesses, or by some record evidence.
Offset line. A supplementary line close to and roughly parallel to a main line at a known distance and
direction from the main line.
Open traverse. A survey traverse that begins on a known control station but does not end at known
control. There is no check whatsoever on the accuracy of such a traverse.
Orientation. The act of establishing the correct relationship in direction with reference to known control or
azimuth. The rotation or the set of rotations needed to make the axes of one rectangular Cartesian
coordinate system parallel to the axes of another.
Original ground. The existing position of the ground surface prior to any construction activities.
Orthometric height. The elevation of a point above or below the geoid. A relationship between ellipsoid
height and orthometric height is obtained from the equation h=H+N where: h = ellipsoid height
H = orthometric height
N = geoid height
In Wisconsin, the geoid height is always a negative value and is approximately -100 feet.
Owner. A person(s) with legal ownership to real or personal property.
Owner/occupant. A person(s) with a legitimate interest in the land or activities on the land which may
include—but is not limited to—the legal owner, renter of buildings or land, occupant, caretaker, farmer of
crops or animals, or neighbor.
Parameter. In general, any quantity of a problem that is not an independent variable.
Peg test. A method of testing and adjusting the collimation of a level instrument.
Pier. A vertical structural member, usually a column supporting beams, girders, etc., between abutments.
Plane rectangular coordinates. A system of coordinates in a horizontal plane, used to describe the
positions of points with respect to an arbitrary origin. The origin is established by a pair of axes which
intersect at a right angle. The position of a point is determined by the perpendicular distances to each of
the axis. Also called plane coordinates.
Plane survey. A survey in which the surface of the Earth is considered a plane. Surveying done under the
assumption that the surface of the Earth is flat.
Planimetric Map. A map representing only the horizontal position of features.
Planimetry. Parts of a map which represent everything except vertical relief.
Plat. A diagram drawn to scale showing land boundaries and subdivisions thereof, together with all data
essential to the description and identification of boundaries shown.
PLSS. Public Land Survey System.
Point of beginning (POB). The point from which a survey is initiated. Also see initial point.
Point of curvature (PC). The point in a line survey where a tangent ends and a circular curve begins.
Point of intersection (PI). The point where two tangents meet.
Point of tangency (PT). The point in a line survey where a circular curve ends and a tangent begins.
Point of vertical curve (PVC). The point of change from a line of uniform slope to a vertical curve.
Point of vertical intersection (PVI). The point of intersection of two lines, each having different slopes.
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Point of vertical tangent (PVT). The point of change from a vertical curve to a line of uniform slope.
Position. Data which define the location of a point with respect to a reference system.
Positional accuracy. A term used in evaluating the overall reliability of the positions of features on a map
or chart relative to their true position, or to an established standard.
Precision. In statistics, a measure of the tendency of a set of random numbers to cluster about a number
determined by the set. It is distinguished from accuracy by the fact that the latter is a measure of the
tendency to cluster about a number (true value) not determined by the set, but specified in a different
manner.
Prism. A corner cube of retro-reflective glass used to transmit light rays back precisely parallel in the
same direction as they are received.
Profile. A vertical representation of a surface along a fixed line of reference.
Preliminary survey. An initial survey which forms the basis for engineering design.
Property survey. A survey to retrace or establish property lines or to establish the locations of structures
within property limits.
Quadrangle. A rectangular area covered by a map or plat, usually bounded by given meridians of
longitude and parallels of latitude.
Radial survey. A survey carried out radially (Azimuth/Distance) from one fixed point.
Random errors. Errors which do not follow physical laws nor can be defined mathematically. As an
example: bubble not centered at the instant a level rod is read.
Random line. A trial line, directed as closely as possible towards a fixed terminal point which is not visible
from the initial point.
Real-Time Kinematic (RTK). A method of positioning using GPS.
Reciprocal vertical angles. Vertical angles measured over a line at both ends in trigonometric leveling to
eliminate the effects of curvature and refraction.
Reference Line. A line used as a reference or base for measuring other quantities. The reference line
may coincide with the centerline or a right-of-way line at some locations.
Relative Accuracy. An evaluation of the positional orientation of one point or feature with respect to
another.
Resection. The determination of horizontal position of a survey station by observed directions or lengths
from the station to points with known positions.
Residual. The difference between any measured quantity and the most probable value for that quantity.
Residual error. The difference between any value of a quantity in a series of observations, corrected for
known systematic errors, and the value of the quantity obtained from the combination or adjustment of that
series.
Reticle. A mark, such as a cross or system of lines, lying in the image plane of a viewing apparatus and
used singly as a reference mark for observations.
Retracement. A term applied to a survey that is made for the purpose of verifying the direction and length
of lines, and identifying the monuments and other marks of an established prior survey.
Right-of-way. A strip of land granted by fee or easement for construction, maintenance, or other
designated use. DOT right-of-way is land owned by DOT for transportation purposes.
Route survey. Preliminary, control, and construction surveys which cover a long but narrow area, as in
transportation corridors.
Scale factor. The multiplying factor used to convert a geodetic distance to a grid distance. A number by
which a distance obtained from a map by computation or measurement is multiplied to obtain the actual
distance on the datum of the map.
Sea level factor. The factor used to convert horizontal ground distances to geodetic (mean sea level)
distances.
Skew. A clockwise angle measured from the back tangent to the centerline of a structure or culvert. Skew
of a structure or culvert is also measured by the method of right hand forward (RHF) or left hand forward
(LHF) when looking in the direction of
skew of 95 is the same as 5
Slope stake. A construction grade stake which marks the outer limits of the grading and is set or offset to
indicate the point where the backslope or fill slope intersects the original ground. It also serves as a
control point from which horizontal and vertical measurements can be made to aid in constructing earth
grades.
Span. The unsupported length of a structure.
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Spiral curve. A transition curve of constantly changing radius.
Stadia constant. The ratio which is multiplied by the stadia interval to obtain the length of a line of sight.
Stadia interval. The length of rod subtended between the top and bottom crosswires in a surveying
instrument.
Stamping The information on a survey disk identifying it from other similar survey disks. The stamping
information normally includes the station (bench mark) designation and the year the monument was first
observed. If other information has been stamped on the disk or logo cap (e.g., an elevation), that
information is considered to be part of the stamping information. Historically, the station designation and
year were hand stamped on the survey disk and were called “the stamping” to differentiate that
information from the inscription information. Also see “inscription
Standard deviation. A value expressing precision which is defined as the square root of the variance.
State plane coordinate system. The plane rectangular coordinate system established by the National
Geodetic Survey for use in defining positions of points in terms of plane rectangular (Y and X) coordinates.
Station (Construction survey). A point on a baseline (often the centerline) that is a specified distance
from the point of commencement.
Station (Geodetic survey). A physical location or site at which, from which, and to which observations
have been made. Usually marked by a permanent monument including a disk with stamped designation.
Superelevation. The banking of a curved section of road to help overcome the effects of centrifugal force.
Survey. The result (product), or anticipated result, of surveying. Examples and usage: a topographic,
hydrographic, public land, geodetic, or GPS survey; a survey marker, monument, disk, station, bench
mark, or crew.
Survey cap. A survey marker, constructed of metal or plastic, designed to fit over the end of a pipe or rod.
The setting agency name may be imprinted on the top of the cap.
Survey disk. A survey marker constructed from a circular piece of flat or domed metal, usually bronze or
aluminum, with a perpendicular stem at the center to anchor the marker in concrete. The stem may be
pushed into fresh concrete or set into a drill hole with epoxy resin. The setting agency name is usually
imprinted and the station name stamped on the disk.
Surveying. The science, art, and technology of determining the relative positions of points above, on, or
beneath the surface of the earth, and portraying such information on paper or in digital files. Activities
include calculating areas, defining boundaries and establishing control based on the points. Examples and
usage: topographic, hydrographic, land, or geodetic surveying; surveying activities, operations, data,
methods, equipment, instruments, or terms.
Surveying operations. Any, or all, field activities to support property boundary surveys, geodetic or
project control surveys, environmental surveys, species and habitat surveys, geotechnical evaluations,
and other fieldwork. "Surveying operations" may range from just walking across a field or along a railroad
track to excavating for soil sampling, archaeological excavation, or survey monument installation.
Systematic error. An error in a measured value which follows some physical law or which can be
expressed as a mathematical function.
Tangent. A straight line, often mentioned with respect to a curve.
Target. The distinctive marking of a ground point to aid in its identification on a photograph.
Three-wire leveling. A method of leveling applied when the reticle of the level has three lines. The rod is
read at each of the three lines and the average is used for the final result.
Tolerance. The maximum allowable variation from a standard or from specified conditions.
Topographic survey. A survey which has for its major purposes the determination of the vertical relief of
the surface of the earth and the location of natural and constructed features thereon.
Total Station. An electronic theodolite combined with an EDMI and an electronic data collector.
Traverse. A method of surveying in which lengths and directions of lines between points are obtained
from field measurements, and used in determining positions of the points.
Triangulation. A method of surveying in which the stations are points located at the vertices of a chain or
network of triangles.
Tribrach. Centering device for mounting surveying equipment on a surveying tripod. The three-armed
base of a surveying instrument, which carries the foot screws used in leveling the instrument.
Trigonometric leveling. The determination of elevation differences from observed vertical angles
combined with the lengths of lines.
Trilateration. A method of surveying wherein the lengths of the triangle sides are measured, and the
angles are computed from the measured lengths.
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True north. The direction from an observer's position to the geographical North Pole.
Turning point. A solid point used in leveling, where an elevation is temporarily established so that the
level may be relocated.
USPLSS. See PLSS.
U.S. Survey Foot. See Foot, U.S. Survey.
UTC. See Coordinated Universal Time
UTM. Universal Transverse Mercator grid system.
Variance. A value by which the precision of any group of measurements is expressed. Defined as the
sum of the squares of the residuals divided by the number of measurements.
Vector. A three-dimensional line between two points, defined by a direction and a magnitude.
Vertical angle. See Zenith Angle.
Vertical control datum. Any level surface (for example mean sea level) taken as a reference from which
to reckon elevations. Although a level surface is not a plane, the vertical control datum is frequently
referred to as the datum plane.
Vertical curve. A parabolic curve joining two gradelines.
Vertical exaggeration. The increase of the vertical scale over the horizontal scale of a terrain model.
Waving the rod. The slight waving of the level rod to and from the instrument, which permits the surveyor
to take a precise (lowest) rod reading.
Weight. The relative worth of an observed value as compared to any other value. A factor by which a
quantity is multiplied to increase or decrease the effect of that quantity on the results of an adjustment.
WisDOT field representative. The Department field person providing daily planning, scheduling, or onsite coordination of the field surveying operations and usually is the liaison with owners in the project area;
is typically a more senior person such as a crew chief, project manager, project leader, lead worker,
specialist, or similarly titled person if working for a consultant, and may be directing other field workers or
working alone.
Witness corner. A monumented survey point usually on the line of survey near a corner. Established as
reference when the corner itself is so situated as to render its monumentation or ready use impracticable.
Witness mark. A mark placed at a known distance and direction from a property corner or survey station
to aid in its recovery and identification.
Wing wall. An abutment extension designed to retain the approach fill.
World Geodetic System of 1984 (WGS 84). A rotational ellipsoid having a semi-major axis of 6,378,137
meters by definition and a semi-minor axis of 6,356,752.31424 meters by calculation. The reference
ellipsoid for the Global Positioning System.
Zenith. That point of the celestial sphere vertically overhead. The point at which a line opposite in
direction from that of the plumb line at a given point on the Earth’s surface meets the celestial sphere.
Zenith angle. A vertical angle measured downward from the zenith direction.
Zone constants. A set of parameters used to define a mapping projection. Such constants include central
meridian, standard parallel, and latitude of origin.
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CHAPTER 1
Types of Surveys
Types of Surveys
Surveying is the science of determining relative positions of points on or near the earth’s surface. The
horizontal positions of these points are computed from distances and directions, and vertical positions
from differences in elevations which are measured individually or in combination to a specified degree of
accuracy, and are in direct relation to a known or determined datum.
Accuracy is a prime consideration in surveying. Instruments for each type of survey are used with
prescribed techniques to achieve a designated accuracy.
Less accuracy than specified results in a survey which will prove useless for its intended purpose; more
accuracy wastes time and effort, and may not improve the final results.
Surveys are normally divided into two general classes: Geodetic and Plane.
Geodetic Surveys
The mathematical shape of the earth is an oblate spheroid (almost a sphere) with a major diameter at the
equator of about 7,920 miles. Distances or areas measured on the surface of the earth are, therefore, not
along straight lines or planes, but are on a curved surface. Geodetic surveys that normally extend over
long distances and cover large areas must have computations to allow for curvature of the earth.
To accomplish this, the earth’s major and minor diameters are computed accurately, and from these a
spheroid reference. The position of each geodetic station is related to this spheroid. The positions are
expressed as latitudes (angles north or south of the equator) and longitudes (angles east and west of the
prime meridian), or as plane coordinates on a rectangular grid system, correlated with the latitude and
longitude. In addition, the plumb line deflection and its effect on relative positions of the stations are
considered in precision work.
Plane Surveys
When the extent of the survey becomes small (less than 100 square miles in area), and when only limited
accuracy is required, the effect of curvature can be ignored. These surveys are treated as if the
measurements were made on a plane and are known as plane surveys.
The difference between plane and geodetic surveying can be expressed in terms of plumb lines. In plane
surveys, plumb lines are considered parallel, while in geodetic surveys convergence is taken into account.
Highway and railroad surveys, which may extend for hundreds of miles, are usually in a narrow strip and
are considered plane surveys. However, a limited computation for the earth’s curvature is necessary in
this case. On a long traverse survey, an astronomic azimuth is determined at intervals of several miles.
The astronomic azimuth establishes an astronomic north-south line and may be used to obtain the true
direction of a survey line. The azimuth values of the lines between astronomic azimuth stations consider
the convergence of the meridians. The methods, operations, and measurements in either type of survey
are similar; but since the distances between stations are usually much greater in geodetic surveying, more
precise equipment and procedures are used.
11
Surveying Field Work
Field work in surveying consists of making and recording measurements. The operations are as follows:
1. Measuring distances and angles to:
o establish points and lines of reference for locating details such as boundary lines, roads,
buildings, fences, rivers, bridges, and other existing features
o stake out or locate roads, buildings, utilities, and other construction projects
o establish lines parallel or at right angles to other lines, measure inaccessible distances as
across rivers, extend straight lines beyond obstacles such as buildings and do any work
that may require use of geometric or trigonometric principles.
2. Measuring differences in elevations and determining elevations to:
o establish permanent points of known elevation (bench marks)
o determine elevations of terrain along a selected line or area for plotting profiles and
computing grade lines
o stake out grades, cuts, and fills for construction projects.
3. Making topographic surveys where in horizontal and vertical measurements are combined.
4. Recording field notes to provide a permanent record of the field work.
Factors Affecting Field Work
The surveyor in the field must constantly be alert to the different conditions he or she encounters and the
requirements of the survey. The weather, terrain, personnel, purpose, and accuracy of the survey,
systematic procedures, and the expected rate of progress are some of the factors that will affect the work.
Physical factors such as terrain and weather will affect each field survey in varying degrees.
Measurements using telescopes can be stopped by fog, mist, or dust. Swamps and flood plains under
high water can impede taping surveys. Lengths of light-wave distance measurements are reduced in
bright sunlight. Generally, reconnaissance will predetermine the conditions and alert the survey party to
the best method to use and the rate of progress to be expected.
The status of training of the personnel is another factor that affects field work. Experience in handling the
survey instruments and equipment can shorten survey time without introducing errors, which would
require resurvey. The personnel factor is a variable that will affect the rate of progress.
The purpose of the survey will determine the needed accuracy, which, in turn, will influence the selection
of instruments and procedures. For instance, comparatively rough procedures can be used in measuring
for earth-moving, but grade and alignment of a highway must be much more precise, and require more
accurate measurements. Each increase in precision also increases the time required to make the
measurement, since greater care and more observations must be taken.
Each survey measurement will be in error to the extent that no measurement is ever exact. Besides
errors, survey measurements are susceptible to mistakes or blunders. These arise from misunderstanding
the problem, poor judgment, confusion on the part of the surveyor, or simply from an oversight. By working
out a systematic procedure, the surveyor will often detect a mistake when some operation seems out of
place.
Survey speed is not the result of hurrying; it is the result of saving time through the following:



the skill of the surveyor in handling his field equipment
the intelligent planning and preparation of the work
the process of making only those measurements that are consistent with the accuracy
requirements.
12
CHAPTER 2
Distance Measurement
Electronic Distance Measurements
The different firm currently has a variety of different electronic total stations which have the capability of
measuring distances with an electronic distance measurement device (EDM) attached or built in to the
instrument. The correct method of operation of each instrument is described in the manufacturer's
operating manual that accompanies each instrument. This procedure describes the elements of precision
distance measuring which are common to most EDM's.
Principle of Measurement
The underlying principle of modern EDM systems is based on the speed of light. A light source is
modulated and transmitted at a very high frequency from the source (electronic total station) to a distant
reflector (prism). The reflector returns the light to the receiving optics of the instrument and these light
pulses are no longer in phase with the outgoing light pulses because it has taken a certain amount of time
to travel from the instrument to the reflector and back again. These light pulses are converted to an
electrical signal which is then compared to a reference signal and a resulting phase delay can be
measured very accurately. This phase delay can then be related to a distance between the instrument and
the reflector. Other methods are used such as timing the light pulse but the phase delay is currently the
most popular among EDM manufacturers.
Sources of Error
Sources of error in EDM work can be categorized as human, instrumental or natural. Human errors
include misreading, improperly setting over stations, improper input of prism offset and incorrectly
measuring meteorological data, staff heights and instrument heights. With careful field procedures these
errors can be eliminated. If EDM equipment is carefully adjusted and precisely calibrated, instrumental
errors should become extremely small and thus negligible. Manufacturers specify the accuracy of an EDM
with a two-part number, such as ±- (5 mm + 5 ppm). The first number, ± 5 mm, means that at any
distance, the EDM can have a spread in distance measured of up to 5 mm from the mean distance. The
second number, ±5 ppm, is a proportional error which varies with the distance measured. These numbers
can change over time and should be periodically verified against a calibrated base line. The National
Geodetic Survey, in cooperation with the WisDOT and the Wisconsin Society of Land Surveyors, has
established eight calibrated base lines throughout the state near the transportation district offices. When
the reduced measurements (compared with the published values) agree within the instrument
manufacturers stated accuracy, the instrument can be considered as being in good calibration.
Natural errors in EDM operations stem primarily from atmospheric variations in temperature and pressure.
The speed of light through the atmosphere changes with temperature and pressure. If the incorrect
temperature and/or pressure are entered, the distance displayed will not be correct. To record the proper
distance, air temperature and pressure should be measured and a ppm correction computed. Air
temperature should be measured in the shade and well above the ground to reduce the effects of ground
radiation. Barometers should be calibrated periodically at the local airport. Barometric air pressures
announced on the local radio station have traditionally been reduced to mean sea level. Air pressure
readings for corrections to EDM distances must be absolute pressure at the station sites. As a rule of
thumb, for every 90 feet above sea level the air pressure drops 0.10 inch. For long lines and lines of great
elevation difference between the end points, temperature and pressure readings should be measured at
both ends.
Prisms
Prisms are used with total stations to reflect the transmitted signals. A single prism is a corner cube of
glass that has the characteristic of reflecting light rays back precisely in the same direction as they are
13
received. Prisms are contained in a plastic or metal housing which can be tribrach mounted on a tripod
and centered over a ground point with the aid of an optical plummet, or they can be attached to a
telescoping range pole held vertical on a point with the aid of a bull's eye level. It should be noted that
prisms should be tribrach mounted if the highest level of accuracy is desired. In control surveys, tribrach
mounted prisms can be detached from their tribrachs and then interchanged with the total station. This
interchangeability of prism and total station is known as “forced centering" or "leap frogging,” which not
only speeds up work but increases accuracy. Manufacturers of prism assemblies specify a certain offset
that must be accounted for when measuring distances. This offset is caused by not having the effective
center of the prism in a direct plumb line over the ground point. This offset distance, usually expressed in
(mm), must be added or subtracted from the measured distance. All EDM's have the capability for the
user to input the proper offset which will be compensated for automatically before the distance is
displayed. It is not good practice to mix prism assemblies of different types or manufacturers. Refer to
manufacturer specifications for the correct offsets of prism assemblies. Total stations are classified as
either coaxial or modular. A coaxial total station has the EDM line of sight in the same plane as the optical
line of sight while a modular total station will have an EDM line of sight above the optical line of sight. The
coaxial configuration is easier to use. When a distance is to be measured, the cross hairs in the telescope
are pointed at a target centered about the prism. Conversely, a total station of the modular type must use
the proper prism and prism-target assembly to account for the difference in the EDM line of sight and the
optical line of sight. Most instrument manufacturers provide prism target assemblies to account for their
particular configuration.
EDM Operation
The operation of all EDM's involves the following basic steps: (1) setup, (2) aim, (3) measure, (4) record. It
should be noted that most EDM's are interfaced with an angle measuring instrument and the combination
of these capabilities results in an instrument termed the Total Station. Refer to the instructions that
accompany the EDM device. The measured data can be recorded conventionally in field book format or
preferably in the AASHTO SDMS electronic data format on an electronic data collector. The slope
distance must be accompanied by all necessary data to properly reduce it to a horizontal distance
component.
Angle Measurement
All theodolites measure angles with some degree of imperfection. These imperfections result from the fact
that no mechanical device can be manufactured with zero error. In the past very specific measuring
techniques were taught and employed by surveyors to compensate for the minor imperfections in
theodolites. With the advent of electronic total stations the imperfections still exist but are corrected in a
different way with somewhat modified field procedures. The Department currently has a variety of total
stations which are utilized for design and construction surveying. The correct method of operation of each
instrument is described in the manufacturer's operating manual which accompanies each instrument. This
procedure describes the elements necessary for measuring precise horizontal and vertical angles which
are common to most total stations.
Total Stations
"Total Station" is the term applied to modern surveying instruments that incorporate an EDM, a digital
theodolite and a microprocessor. This combination of components provides the capability of electronically
making simultaneous slope distance and horizontal and vertical angle measurements. Total stations
measure very rapidly and display the data automatically in digital format. The microprocessors within the
total station display the horizontal and vertical components of sloping lines in real time. Total stations can
also be connected to data collectors which enable the automatic recording of field measurements for
further processing and plotting capabilities.
14
Horizontal Angles
When measuring horizontal angles, the choice of a proper total station depends on the level of accuracy
desired. For control surveys, a total station with a stated accuracy of one arc second is most adequate.
For construction surveys, a total station with a stated accuracy of six arc seconds is adequate. At each
station occupied with a total station, the interior clockwise angle between the lines of sight to stations
observed will eventually be determined by taking differences between their relative directions expressed in
angular units.
A “position” is defined as one observation of the horizontal direction from an arbitrarily selected initial
station to each of the other stations, with the telescope both direct and reversed. For greatest precision, a
number of positions are turned and the mean is used for further computations. The number of positions
required to turn varies depending on the accuracy of the survey desired. Any position that deviates ± 5
seconds from the mean should be rejected and re-observed.
Vertical/Zenith Angles
The vertical angle measured by a total station is not a true vertical angle but rather a zenith angle. The
angle measured is the clockwise angle measured from zenith (the point directly above the instrument).
The measurement of vertical angles throughout a survey allows for the proper reduction of slope distances
to horizontal distances as well as computation of elevation differences between stations sighted. For
control surveys, two positions should be observed for each line. Any position that deviates ± 10 seconds
from the mean should be rejected and re-observed. It is recommended vertical angles be observed from
both ends of the line to reduce effects of earth curvature and refraction. When reciprocal vertical angle
observations are not practical or warranted for some surveys, it should be remembered that in order to
minimize the errors introduced by curvature and refraction, sight distances should be restricted to less
than 800 feet (240 m).
15
CHAPTER 3
Computations
The Department currently uses a variety of software packages and computer programs for data reduction
and adjustment of horizontal control. The correct method of operation of each package or program is
described in the appropriate user manual for each. This procedure describes some of the fundamental
computations which the above programs accomplish as well as provides some general guidelines for
proper horizontal control adjustment.
Horizontal and Vertical Angle Reduction
Horizontal and vertical angles should be validated and reduced to a mean angle. They should be checked
to verify that correct observational procedures were employed for the accuracy of survey desired. This
includes verification of number of positions turned, re-observation of rejected positions and ensuring that
all necessary information was recorded for proper reduction. Some total stations will perform this reduction
in real time while out in the field. For instruments of this type only the mean angles are recorded, thus it is
important to record in arc seconds the appropriate errors of the horizontal and vertical pointing. These
error values are important for the proper weighting of that angle in the least squares adjustment program.
Horizontal and Vertical Distance Reduction
The actual observations made with a total station are horizontal angle, vertical (zenith) angle and slope
distance, from the instrument to the prism/target assembly. These observations can be used to generate
the horizontal distance and vertical distance (difference in elevation).
The figure below shows an instrument measuring a slope distance (DS) and a vertical (zenith) angle (VT).
The horizontal distance, (DH), can be determined by the equation:
DH=DS*sinVT
The vertical distance, (DV), can be determined by the equation:
DV=DS*cosVT
The accuracy of either the horizontal or vertical distance is directly related to the accuracy of the
measured slope distance and, more critically, the zenith angle. By taking direct and reverse vertical angle
pointing, errors in the measurement of the zenith angle can be minimized.
Curvature and Refraction
If the horizontal and vertical distances are computed by only multiplying the measured slope distance by
the sine and cosine of the measured vertical angle respectively, the errors can be considerable due to the
effects of earth curvature and refraction. Ideally, the surveyor should measure the reciprocal zenith angles
and slope distances from both ends of the line and use the mean value to correct for earth curvature and
refraction. However, this is not always practical or warranted. Thus, all total stations and reduction
programs are capable of applying a correction based on a simple formula with assumed values for earth
radius (Re) and a refraction constant (K). This correction will be applied each time a horizontal or vertical
distance is displayed on the total station or can be applied during office reductions with any of the
accepted programs.
The standard formulas used by most total stations and software programs are as follows:
DH = DS * sin (VT) - (DS) 2 * sin 2 (VT) * (1 - K)[ ] [ 2Re 2 ]
DV = DS * cos (VT) + (DS) 2 * sin 2 (VT) * (1 - K)[ ] [ 2Re ]
16
DS = Slope Distance
DH = Horizontal Distance
DV = Vertical Distance
VT = Zenith Angle
Re = Radius of Earth - 20,902,000 ft (6,372,000 m)
K = Refraction constant mean = 0.142
17
CHAPTER 4
LEVELING
Leveling is the term applied to any of the various processes by which elevations of points or differences in
elevation are determined. It is a vital operation in producing necessary data for planning, mapping, design
and construction. The most common method used in leveling is differential leveling.
Double Run Leveling
With this technique a double line of levels is run through a single line of turn points. At each setup site, two
independent IH's are established at approximately 0.5 foot (150 mm) difference. From each IH a single
wire rod reading is obtained on the single backsight and foresight turn point. The average adjusted
elevations from the two lines are then used
Reciprocal Leveling
The surveyor should always try to keep backsight and foresight distances equal during differential leveling
so that instrument and natural errors cancel out. In some situations, such as river or valley crossings, this
is not always possible. The reciprocal leveling technique should then be utilized, this technique is
illustrated in Figure 1 below. The level is set up and readings are taken on TP3 and TP4. (Precision can
be improved if multiple readings are taken on the turn points and then averaged.) The instrument is then
moved to the other side and the process is repeated. The differences in elevation thus obtained are
averaged to obtain the final result. The averaging process should eliminate instrumental and natural errors
such as curvature and refraction.
Trigonometric Leveling
The use of a total station as a level increases acceptable distances on sight lines and can increase
production in many situations. The difference in elevation between any two points can be determined if the
vertical angle (VT) and slope distance (DS) of the line from one point to the other are measured. With
modern total stations, the elevation difference can be calculated automatically but an understanding of the
formulas used and what the different combinations of Instrument Height (IH) and Staff Height (SH) will
produce in the form of displayed or recorded results is necessary. Figure 2 below shows a total station
measuring a slope distance and vertical angle. The vertical distance, (DV), can be determined by the
equation:
DV = DS * cos (VT)
If the ground elevation at the instrument is known,
Ground Elev @ Target = Ground Elev @ Instr + IH = DV – SH
In order to get elevation difference from ground point to ground point, the IH must be added and the SH
subtracted from the DV. The keys to success in running trigonometric elevations is to take the mean direct
and reverse readings of the vertical circle, limit sight distances to less than 1000 ft (300 m), and use
proper targeting. Deviations from these procedures can result in large errors due to the effects of earth
curvature and refraction.
Digital Leveling
Recent advances in electronics now enable surveyors to perform differential leveling with an electronic
digital level. The digital level processes an electronic image of a bar coded staff for determination of
heights and distances with automatic recording of the data for future processing on a computer. The digital
level is an automatic level (pendulum compensator) capable of normal optical leveling with normal
graduated staffs. The level can also be used with the bar coded staff and rod readings obtained digitally
with output units in either metric or standard English units.
18
Curvature and Refraction
All elevations are referenced to level lines (surfaces), while the line of sight through a level is in fact almost
a horizontal line. Thus, all rod readings taken with a level will contain an error (C) due to earth curvature. It
should also be noted that all sight lines are refracted downward (R) by the earth's atmosphere. The
surveyor should be aware of the combined effects of curvature and refraction (C and R) and account for it
by balancing backsight (BS) and foresight (FS) distances to cancel the error. For the most part this error is
insignificant but it could be a problem on long level lines where BS and FS distances were not balanced.