Auburn: Surveying Test #1

Surveying

(Geomatics) Science, art & technology, of determining relative positions of points.

All methods for measuring & collecting information about earth

Tasks of a surveyor

1) Measure & represent land, 3D objects, point fields, etc;

2) Interpret land & geographically related data

3) Use information for planning & administration of land

4) Conduct research into above practices

Detailed Functions of a Surveyor 1

1. Determine shape & size of earth

2. Position of objects

3. Development/testing of instruments

4. Acquisition/use spacial info

5.Determination of position of boundary

6.Design, establishment, admin. of GIS

Detailed Functions of a surveyor 2

7. Analysis, interpretation,, integration of spatial objects in GIS

8. Study of natural and social environment

9. Planning/development of property

10.Assessment of property value

11.Planning, measurement, management of construction works

GIS

Geographic Information System

GNSS

Global Navigation Satellite System

GPS

Global Positioning System

Survey Classifications

Geodetic & Plane

Geodetic Survey

Curved surface of the earth is considered. Calculations are performed assuming earth's surface to be an ellipsoid

Plane Survey

Earth's surface considered to be flat. Except for leveling, reference base for fieldwork is assumed to be a flat surface

Specialized Types of Surveys

Topographic, Land, Boundary, Cadastral, Hydrographic, Alignment, Construction, As-built

Topographic Survey

Used in map making, determines location of features & elevations

Land, Boundary, Cadastral

Establish property lines & corner markers

Original - establish new section corners

retracement - recover previously established boundaries

subdivision - delineate new parcels of ownership

Hydrographic Survey

surveys to define shoreline & depths of bodies of water

Alignment Survey

Linear construction; plane, design, construct highways, railways, etc. Starts at one point and proceeds in a straight line

Construction Survey

provides line, grade, control elevations, etc. for construction operations

LIS

Land Information System

NGS

National Geodetic Survey

USGS

U.S. Geological Survey

BLM

Bureau of Land Management

Observations forming the basis of plane surveying

1) horizontal angles

2) horizontal distances

3) vertical (zenith) angles

4) vertical distances

5) slope distances

1"

0.0833'

1 sq mile

640 acres

1 Gunter's Chain (ch)

66Ft, 100 lk

1 mile

5280Ft, 80 Gunter's Chain

1 Degree

60 min, 3600 seconds

1 min, 1 sec

1/60 degrees, 1/3600 degreres

Leading 0's are

insignificant

Addition/Subtraction sigfig rule

round to least accurate decimal place EX: 12.345 + 6.7 = 19.0

Multiplication/Division sigfig rule

count sigfigs, round to smallest number of sigfigs

Ex: 1.23 * 4.5678 = 5.62

Field note items located top of right page

1) project name, location, time

2) weather

3) party

4) instrument type

Field note requirements:

Accuracy, Integrity, Legibility, Arrangement, Clarity

Kinds of field notes

Sketches, tabulations, descriptions, combinations

Direct Observation

an observation taken directly, such as measuring a distance w/ a ruler

Indirect observation

An observation taken indirectly, used when a direct observation isn't an option. Ex: an observation made by calculation

Error

E = X - _X ; X = observed value, _X = true value

General rules about error

1) no observation is exact

2) every observation contains errors

3) the true value of an observation is NEVER known

4) the exact error present is always unknown

Mistakes

(blunders) Can be avoided with care; mistakes are not errors

Sources of error

natural, instrumental, personal

Types of error

systematic and random

Systematic error

Error that shifts all measurements in a standardized way. Decreases accuracy. Can result in bias

Random error

error caused by factors beyond the control of the observer; present in all surveying observations

Precision

degree of consistency

Accuracy

how close a measurement is to the true value

What to do when mistake is detected?

retake measurement or rerun the calculation. If enough data points are present, mistake can be discarded

Most probable value (_M)

_M = sum M / n ; sum(M) = sum of individual observations, n = number of observations

Residual (v)

v = _M - M ; _M = most probable value, M = any observation

Small errors occur

more often than large ones

Positive & negative errors...

occur at the same frequency

Standard deviation

o- = sqrt( sum(v^2) / n - 1 )

variance

standard deviation squared

Least squares adjustment

Sum of weights of observations multiplied by corresponding squared residuals

Leveling

various processes by which elevations of points or differences in elevations are determined

Leveling results are used for _____

1) design of highway, railway, etc. that conforms to existing topography

2)lay out construction projects

3) calc. volumes of mats.

4) find drainage characterists of an area

5) develop maps

6) study earth subsidence

Leveling terms

Vertical line, level surface, horizontal plane, horizontal line, vertical datum, elevation, geoid

NAVD88

North American Vertical Datum of 1988; the vertical datum used for much geospatial data in North America

Mean Sea Level

No longer applicable; average height for surface of seas

Benchmark

relatively permanent object having marked elevation; ex. metal disk set in concrete

Leveling

process of finding elevations or their differences

Vertical control

A series of benchmarks or other points of known elevation established throughout an area, also termed basic control or level control.

Differential Leveling

The process of determining the difference in height between a plane of sight and a point.

Barometric Leveling

Involves the determination of differences in elevation between points by measuring the variation in atmospheric pressure at each point by means of a barometer.

Trigonometric Leveling

Determining elevations by measuring the slope distance and vertical angles between points

Calculating the difference in elevation using trigonometry

Types of levels

Dumpy, tilting, automatic, & digital

Tilting level

It consists of a telescope attached with a level tube which can be tilted within few degrees in a vertical plane by a tilting screw.

Tripod

a three-footed stand often used to balance a camera

Level rod

large ruler, used with a level to determine elevations

Automatic level

A surveyor's level whose line of sight is automatically maintained in the horizontal plane, once the instrument is roughly leveled.

Engineers level

must be manually set up

Profile leveling

differential level w/ addition of intermediate minus sights (foresights) taken at regarded points

Waving

swing level rod back and forth for the other surveyor to determine if the rod if vertical

Errors in leveling

instrumental, natural, personal

Distance to leveling rod

(top stadia - bottom stadia) * 100

HI =

Elevation + BS

Elev =

HI - FS

Mistakes in leveling

reading level rod wrong, recording error, bumping into tripod, etc.

Methods for obtaining linear methods

Pacing, odometer, optical range finder, tacheometry, taping, Electronic distance measurement (EDM)

GNSS

Global Navigation Satellite Systems, the term used for navigational satellites

Triangulation

Method for determining points from which horizontal distances can be computed

Steps for Taping

Lining in, apply tension, plumbing, marking tape length, reading tape, record distacne

Taping direction of a slope

Downhill

Error in taping

Instrumental, Natural, Personal

GIS

Geographic Information System, A computer system that stores, organizes, analyzes, and displays geographic data.

GIS classification

Spatial, Non-spatial

Spatial GIS data

(graphic) shown w/ lines or symbols pn maps, images in photos, data must be represented with simple spatial objects

Non-spatial GIS data

attribute/descriptive data, alphanumeric, includes information like color, texture, quantity, quality, & value of features

Simple spatial data

point, line, interior area, pixel

Metadata

data about data, describes content, quality, condition, & other characteristics about geospatial data

FGDC

Federal Geographic Data Committee

Data Sources

DRG, DEM, DLG

Quadrangles (tacts)

24 mile square

Township (16)

6 miles square, 36 square miles

Sections (36)

1 mile square; 80ch by 80ch

Subdivisions of sections

determined by local surveyors