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Surveying

Surveying . Data for a GIS. Raster data - characteristics? - sources? Vector data - characteristics? - sources?. Bottom: Elements of Surveying . U. S. Army, TM 5-232, 1971. History of surveying. Babylon: knew 3-4-5 triangle; developed base-60 system

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Surveying

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  1. Surveying CS 128/ES 228 - Lecture 10a

  2. Data for a GIS • Raster data- characteristics?- sources? • Vector data- characteristics?- sources? Bottom: Elements of Surveying. U. S. Army, TM 5-232, 1971 CS 128/ES 228 - Lecture 10a

  3. History of surveying • Babylon: knew 3-4-5 triangle; developed base-60 system • Egypt: used simple plumb line sighting & right-angle instruments. • Great pyramid: base square to 0.2 m out of 230 (0.09%) Top: The Roman Land Surveyors. O. A. W. Dilke, 1971 CS 128/ES 228 - Lecture 10a

  4. The motive for surveying? The priests also said that this king divided the country among all the Egyptians, giving each an equal square plot. This was the source of his revenue, as he made them pay a fixed annual tax. If anyone’s land were taken away by the river, he came to the king and told him what had happened. Then the king sent men to look at the land and measure how much less it was, so that in future the owner would pay the due proportion. Herodotus, referring perhaps to Sesostris II of Egypt (1897-1878 BC). From:Dilke. The Roman Land Surveyors. Barnes & Noble, NY. 1971. CS 128/ES 228 - Lecture 10a

  5. Two types of surveys • Geodetic survey- covers distances large enough that curvature of Earth is significant - establishes network of precisely located controlpoints • Plane survey [not ‘plain’]- straight lines & angles are sufficient- what about long, linear features? CS 128/ES 228 - Lecture 10a

  6. National Geodetic Survey Functions: • defines & manages the National Spatial Reference System • sets standards for geodetic surveys • maintains a database of U. S. geodetic markers www.ngs.noaa.gov CS 128/ES 228 - Lecture 10a

  7. NGSurvey data sheets CS 128/ES 228 - Lecture 10a

  8. Uses for plane surveys • Land survey • Engineering or construction surveys • Field mapping Top: Plane Table Mapping. M. Denny. www.pobonline.com...Bottom: www.tpub.com/engbas/11-24.htm CS 128/ES 228 - Lecture 10a

  9. Basic methods • Locating a point • Measuring an angle • Measuring a distance • Measuring differences in elevation CS 128/ES 228 - Lecture 10a

  10. Locating a point • Start with known location or previous point • Direction + distance common for plane surveys (ex. “metes & bounds”) • Two angles common for geodesy Principles of Surveying. 2nd ed. C. A. Herubin, 1978 CS 128/ES 228 - Lecture 10a

  11. Measuring an angle • Horizontal angles: use level, transit, or theodolite • Vertical angle: use transit or theodolite • Either:- graduated circles or- digital readout Both: Principles of Surveying.2nd ed. C. A. Herubin, 1978 CS 128/ES 228 - Lecture 10a

  12. Angles: readability • Horizontal & vertical circles typically graduated to 1o for construction grade instruments, 5’ or better for survey instruments • Vernier improves resolution by 10x or better Principles of Surveying. 2nd ed. C. A. Herubin, 1978 • Digital readouts to 5” or better CS 128/ES 228 - Lecture 10a

  13. Measuring a distance • Start with known location or previous point • Three techniques:1. Taping2. Stadia markings3. Electronic distance measurements (EDM) CS 128/ES 228 - Lecture 10a

  14. Taping: errors (& fixes) • Alignment – plumb bob • Tension – tension handle (or experience) • Thermal expansion – correction tables • Slope - cosines Diagram: www.benmeadows.com CS 128/ES 228 - Lecture 10a

  15. Stadia markings + rod • stadia hairs define a known vertical angle • horiz. distance = 100x vertical • less accurate than taping but faster Both: Principles of Surveying. 2nd ed. C. A. Herubin, 1978 CS 128/ES 228 - Lecture 10a

  16. Electronic Distance Measurement • Optical: uses parallax. Inexpensive but error ≥ 1% • Ultrasonic: mid-priced.Accuracy ~ 0.1% • Laser: moderate to very expensive. Accuracy 1 ppt or better CS 128/ES 228 - Lecture 10a

  17. Measuring elevations • Known as “leveling” • Uses a level (optical or laser) & a rod • All measurements are relative (to a starting elevation) • Height of instrument Both: Elements of Surveying. U. S. Army, TM 5-232, 1971 CS 128/ES 228 - Lecture 10a

  18. Optical vs. laser leveling • Optical leveling requires 2 workers • Laser leveling can be done alone, but easiest when rod is equipped with autodetector (high/low/on signals) Top: Principles of Surveying. 2nd ed. C. A. Herubin, 1978Bottom: Topcon web site CS 128/ES 228 - Lecture 10a

  19. Putting it together Two ways of mapping a region: • Traversing – used to locate specific features • Triangulation – used to establish a control network over a region Both: Elements of Surveying. U. S. Army, TM 5-232, 1971 CS 128/ES 228 - Lecture 10a

  20. Types of traverses Allowable “misclosure” • First order, Class I:- 4 mm in 1 km- 127 mm in 1000 km • Third order:- 12 mm in 1 km- 380 mm in 1000 km • Land surveys: ??? Both: Elements of Surveying. U. S. Army, TM 5-232, 1971 CS 128/ES 228 - Lecture 10a

  21. The total station • Combines theodolite, EDM, data logger & surveying software • Log ~ 8000 points, download data to computer • Why doesn’t ES have one??? CS 128/ES 228 - Lecture 10a Topcon web site

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