Land Surveying

Definition of Surveying in the State of Tennessee (T.C.A. 62-18-102)

Any service of work, the adequate performance of which involves the application of special knowledge of the principles of mathematics, the related physical and applied sciences, and the relevant requirements of law for adequate evidence to the act of measuring and locating lines, angles, elevations, natural and man-made features …for the purpose of determining areas and volumes, for the monumenting of property boundaries, and for the platting and layout of lands and subdivisions thereof, including the topography, drainage, alignment and grades of streets, and for the preparation and perpetuation of maps, records, plats, field notes, records and property descriptions that represent these surveys.

Famous Land Surveyors• George Washington

Surveyor General in Virginia, 1749

• Thomas JeffersonCounty Surveyor for Albemarle County, VA, 1773

• Lewis and ClarkExpedition to explore and survey the west

• Daniel BooneResolved Kentucky land disputes

• Abraham LincolnSurveyor in Illinois when elected to state legislature

Land Surveying

The science of determining the relative positions of points on the Earth’s surface.

– Geodetic Surveys

– Plane Surveys

Geodetic Survey• Takes into account the true size, shape, and

gravity fields of the Earth– The geoid is the equipotential surface of the

Earth’s gravity field which best fits global mean sea level

• Provides significant precision

• Establishes highly accurate control networks

Images courtesy NOAAhttp://celebrating200years.noaa.gov/foundations/gravity_surveys/

Plane Survey• Assumes the Earth’s surface to be a plane (flat)• More common than geodetic surveys• Precise enough for small-scale surveys in a

limited area, such as a construction site• Used to determine legal boundaries,

construction surveys, and small-area topographic or control surveys

©iStockphoto.com

Horizontal Plane

Rod

Geodetic Survey Line of equal elevation

Plane Survey Line of equal elevation

Geoid or other Datum

Geodetic vs. Plane Survey

Earth’s surface

Rod

Types of Surveys

• Control Survey

• Topographic Survey

• Property Survey

• Site Survey

• Construction Survey

Control SurveyEstablish precise horizontal and vertical positions of points that serve as a reference for other surveys

Courtesy Department of Public Works, Seminole County, FL

Photos Courtesy NOAA

Topographic Survey

Gathers data on the location of natural and man-made features, contours, and ground elevation to create a topographic map

Courtesy USGS

Property Survey(or Boundary Survey)

• Establishes property lines for a lot

• Used to create a plat

Site Survey(Plot Survey or Lot Survey)

• Combination of a property survey and topographic survey

• May be required to receive a construction permit

Construction SurveyLocates points and elevations that can be used to establish correct locations and elevations for engineering and architectural projects

Courtesy Isle of Palms, SC Recreation Department

National Spatial Reference System (NSRS)

Common set of reference points for all surveys

Horizontal Datum = Collection of points of known latitude and longitude

Vertical Datum = Collection of points of known elevation

Benchmark (BM) = Permanent mark that establishes a point of known elevation

Wikimedia.org

Courtesy NOAA http://oceanservice.noaa.gov/education/kits/geodesy/geo05_horizdatum.html

Reference System DataInformation on datum points available at http://www.ngs.noaa.gov/cgi-bin/datasheet.prl

Example Data Sheet

Optical EquipmentRequires a visual line-of-sight

A theodolite measures vertical and horizontal angles

A total station is an electronic/optical surveying instrument

©iStockphoto.com ©iStockphoto.com

Optical Equipment

Automatic (Auto) Level

• Commonly used on building sites

• Internal compensator can automatically level the instrument

• Measures difference in elevation between the line of sight and a point

Kennedy

Other Equipment

Courtesy USGS http://gallery.usgs.gov/photos/07_22_2009_j51Qi76Hgb_07_22_2009_13

TripodLeveling Rod

Professional Tape Measure

©iStockphoto.com

Field Book

Kennedy

Kennedy

Kennedy

Kennedy

GPS TechnologyGlobal Positioning System

• A global navigation satellite system

• Developed by the U.S. Department of Defense

• A constellation of satellites that broadcast radio signals

• Receivers intercept several satellite signals in order to determine precise location

Courtesy NASA

Widimedia.com

GPS

©iStockphoto.com

Kennedy

Auto Level

Bulls Eye Level

Telescope

Leveling Screws

Horizontal Angle Rotation Ring

EyepieceHorizontal Tangent Knob

Sight

Diopter Adjustment Ring

Mirror

Kennedy

Reading the Rod

View through the telescope

Horizontal crosshair

Verticalcrosshair

Stadia hairs

Beveled hatch marks

Reading the Rod

Upper Stadia Reading = 5.30 ft

Rod Reading = 5.25 ft

Lower Stadia Reading = 5.20 ft

Stadia Readings• Estimate distance between rod

and instrument• Rod intercept is the difference

between stadia readings

• Estimated distance

• Stadia multiplier typically = 100– Indicated on inside of instrument

case or in Instructional Manual

Stadia Readings

Upper Stadia Reading = 5.30 ft

Lower Stadia Reading = 5.20 ft

Rod Intercept = 0.10 ft

Stadia Reading

Rod Reading = 5.06 ft

Lower Stadia = 4.99 ft

Upper Stadia = 5.13 ft

Read the Rod

Instrument

Point of Unknown Elevation

Differential Leveling

The establishment of differences in elevation between two or more points with respect to a datum

BM

RodRod

Differential Leveling

Elev. 350.00 ft

Differential Leveling

• Start with point of known elevation

Benchmark (BM)

Point of Reference (POR)

Rod reading7.59 ft (BS)

7.59

ft

• Sight to rod on BMBacksight (BS)

• Height of Instrument (HI)HI = BM elev + BS

HI = 350.00 + 7.59 = 357.59 ft

357.59 ft (HI)

357.

59 f

t

Field Notes    AUTO LEVEL READINGS  

          STADIA  

PT(+)BS HI

(-)FS ELEV

TOP/BOT STADIA

DIST/Angle

           

 BM        350.00                                                                                                           

7.59 357.59 7.85 / 7.33 52 ft

Differential LevelingWithout moving the tripod,

• Sight to rod on point of unknown elevation

Foresight (FS)

• Identify elevation of point

Elev.355.23 ft

Rod reading2.36 ft (FS) 2.

36

ft

Point of Interest

Elev = HI - FS

Elev = 357.59 – 2.36 = 355.23 ft

Field Notes

    AUTO LEVEL READINGS  

          STADIA  

PT(+)BS HI

(-)FS ELEV

TOP/BOT STADIA

DIST/Angle

           

 BM  7.59 357.59    350.00 7.85 / 7.33   52 ft

                                                                                                       

xPT- A

2.36 355.23 2.54 / 2.19 35 ft

Differential Leveling

2.36 ft (FS)

7.59 ft (BS)

Field Notes

    AUTO LEVEL READINGS  

          STADIA  

PT(+)BS HI

(-)FS ELEV

TOP/BOT STADIA

DIST/Angle

           

 BM  7.59 357.59    350.00 7.85 / 7.33   52 ft

 PT-A     2.36  355.23  2.54 / 2.19  35 ft

         

             

                                                                 

x

PT- B

4.17 353.42

PT-C 12.91 344.684.40 / 3.93 47 ft

13.21 / 12.61 60 ft

Image Sources

Sanford, F. (2006). Seminole County geodetic control points. Seminole County, Florida: Department of Public Works.

United States Geological Survey (USGS)

National Oceanographic and Atmospheric Administration Photo Library http://www.photolib.noaa.gov/cgs/marks1.html

Istockphoto.com