CS 128/ES 228 - Lecture 10a1 Surveying. CS 128/ES 228 - Lecture 10a2 Data for a GIS Raster data -...

CS 128/ES 228 - Lecture 10a 1

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

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


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.


Two types of surveys

Geodetic survey- covers distances large enough that curvature of Earth is significant - establishes network of precisely located control points

Plane survey [not ‘plain’]- straight lines & angles are sufficient- what about long, linear features?


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


NGSurvey data sheets


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


Basic methods

Locating a point

Measuring an angle

Measuring a distance

Measuring differences in elevation


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


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


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

Digital readouts to 5” or better

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


Measuring a distance

Start with known location or previous point

Three techniques:1. Taping

2. Stadia markings

3. Electronic distance measurements (EDM)


Taping: errors (& fixes)

Alignment – plumb bob

Tension – tension handle (or experience)

Thermal expansion – correction tables

Slope - cosines

Diagram: www.benmeadows.com


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


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


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


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


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



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: ???



The total station

Combines theodolite, EDM, data logger & surveying software

Log ~ 8000 points, download data to computer

Why doesn’t ES have one???

Topcon web site

CS 128/ES 228 - Lecture 10a1 Surveying. CS 128/ES 228 - Lecture 10a2 Data for a GIS Raster data -...

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