Post on 18-Dec-2015
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 control points
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 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
Digital readouts to 5” or better
Principles of Surveying. 2nd ed. C. A. Herubin, 1978
CS 128/ES 228 - Lecture 10a 13
Measuring a distance
Start with known location or previous point
Three techniques:1. Taping
2. Stadia markings
3. 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