Surveying

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# Surveying - PowerPoint PPT Presentation

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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### Surveying

CS 128/ES 228 - Lecture 10a

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

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

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

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

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

NGSurvey data sheets

CS 128/ES 228 - Lecture 10a

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

Basic methods
• Locating a point
• Measuring an angle
• Measuring a distance
• Measuring differences in elevation

CS 128/ES 228 - Lecture 10a

Locating a 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

Measuring an angle
• Horizontal angles: use level, transit, or theodolite
• Vertical angle: use transit or theodolite

Both: Principles of Surveying.2nd ed. C. A. Herubin, 1978

CS 128/ES 228 - Lecture 10a

• 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

Measuring a distance
• Three techniques:1. Taping2. Stadia markings3. Electronic distance measurements (EDM)

CS 128/ES 228 - Lecture 10a

Taping: errors (& fixes)
• Alignment – plumb bob
• Tension – tension handle (or experience)
• Thermal expansion – correction tables
• Slope - cosines

CS 128/ES 228 - Lecture 10a

• 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

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

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

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

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

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

The total station
• Combines theodolite, EDM, data logger & surveying software