CH TER

Traditional SurveyPosit ioning Techniques

Orr.. knowledge is available on the size and shape of the earth, the nextquestion is "Where are we on that earth?" or "Where on earth are we?"(figure 18).

One of the main functions of geodesy is to determine the exact positions ofpoints on or near the earth's surface. This includes points below the surface formining or tunneling, under the oceans for underwater engineering structuresor oil wells, and above the surf'ace for rocketry or radio telescope positioning.

Recent years have seen the traditional techniques supplemented by newones. It would now seem to be only a matter of time before the older methodsare fully superseded by satellite methods and the need for permanent surveymarks disappears. This is not to suggest that all marks would be destroyed orlet fall into disrepair since undoubtedly there would still be small operatorswho would require them.

This chapter will concentrate on the time-honored approaches, and laterchapters will cover the newer techniques. While there is interest in all threespatial dimensions, it is convenient to separate the horizontal positioningfrom the vertical element since in traditional survey work they tended to beseparate operations. With the newer methods this is not so since the dataused can normally solve for all three dimensions at the same time.

Horizontal positioning methods includel. astronomical techniques 3. trilateration2. triangulation 4. traversing

while positioning in the vertical plane includesl. precise or geodetic leveling, 3. barometric leveling2. trigonometric leveling 4. echo sounding

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Traditional Survey Positioning Techniques

North Pole(celest ia l )

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From the very early days ofpositioning. Until the last fsfar easier to find than was thehad to await the invention oflatitude was relatively straighastronomywas used for marinein uncharted regions. Thenmeasurements to establish

Single isolated fixes bysurveyor, because they couldwere connected by other

From early times itwasthe heavens and that there rrarEven before the idea of anby traveling north or south thcby amounts that could bethe surveyor, as well as thevisible in the Southern Henithe position of the Southconstellation known as theany time requires computati

In the early centuries a-fteras many of the heavenlyPrimative observatories carDedge of the movements andpreciated.

Arnong the methods usedcelestial sphere are those

Zen i th North Pole(celest ia l )

Hor izonplane

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19. Celest ia l Coordinate Systems

l.2.3.

by right ascension (RA)by hour angle (HA) andby azimuth (Az) and

where

right ascension : the anglcpointcircle of,

declination the arc

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Traditional Survey Positioning Techniques

HORIZONTAL POSITIONING

Astronomical Techniques

From tJre very early days of civilization the heavens have been used to aidpositioning. Until the last few centuries the N-S component, or latitud,e, wasfar easier to find than was the E-W component, or longitude. While the latterhad to await the invention of good chronometers getting an indication oflatitude was relatively straightforward using simple stellar observation. Initiallyastronomywas used for marine navigation; later explorers found itvery usefulin uncharted regions. Then the geodesist used it in combination with othermeasurements to establish precise positions on which to base national surveys.

Single isolated fixes by astronomical methods were of little value to thesurveyor, because they could not be interrelated. But taken at positions thatwere connected by other means, they were of extreme importance.

From early times it was recognized that the stars appeared to rotate aroundthe heavens and that there was a star near to the apparent hub of that rotation.Even before the idea of an Equator was fully appreciated, itwas observed thatby traveling north or south the elevation of this hub star (Pole Star) changedby amounts that could be related to the distance traveled. Unfortunately forthe surveyor, as well as the navigator and explorer, there is no equivalent starvisible in the Southern Hemisphere that gives a direct approximation tothe position of the South Pole. The nearest star there is o Octantis in theconstellation known as the Southern Cross, but its relationship to the pole atany time requires computation.

In the early centuries after Christ, strenuous efforts were made to catalogueas many of the heavenly bodies as possible in terms of their relative positions.Primative observatories came and went as the importance of detailed knowl-edge of the movements and positions of the stars and planets came to be ap-preciated.

Among the methods used for describing the positions of the stars on acelestial sphere are those shown in figure 19:

l. by right ascension (RA) and declination (6) (figure l9a)2. by hour angle (HA) and declination (6) (figure l9a)3. by azimuth (Ar) and altitude (a) (figure 19b)

where

right ascension : the angle along the celestial equator from an initial

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declination : the arc between the body and the celestial equator

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Traditional Survey positioning Techniques

Theodol i te c i rc leAngle AOB = q

= Direct ion B - Direct ion A= I08" 24' Il" - I4o 32, 29,,= 93"5I '42"

Traditional Strl

: the angle b{Greenwich d

: the horizon(the meridiad

: the vertical ibody

iOf the three systems, the firsr

is independent of the observer'sfield observations in conjunctiontation.

The 17th century saw rhethe Academy of Sciences in Fencourage these among numercfoundation of the Royal GreenrriKing Charles II and with John Flnother major observatories on tiestimuli to production of accurateimprovements in the methods of

Astronomical methods forlatitude and longitude, althougha rectangular coordinate systemare also normally interested in thefound from similar observations_

Azimuth, bearing, and directionure 20). The azimuthfrom point

-{at,4 between the plane containingB. There are subtle differences betazimuth. The former relates toadopted ellipsoid.

The term bearingis normallvgrid north when working in terrns

Direction is used to denote t}le