horizontal positioning methods

8/19/2019 Horizontal Positioning Methods

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HORIZONTALPOSITIONING

METHODS#4th week#


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he Geometry of Making Surveys

A survey network isa group of surveypoints all inter-connected such that

they are all in acommon coordinatesystem.

Triangulation

Triangulation is a type of surveying that uses the

principles of trigonometry to determine positions on thesurface of the Earth (i.e., latitude and longitude). If the

three angles of a triangle and the length of one side of

the triangle are known, the lengths of the other two

sides of the triangle can be computed.


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Trilateration


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Traverse A traverse is a series

of survey points, often

laid out in

approximately a

straight line.

A traverse starts from two known points to provide

position and aimuth (direction) for the survey and

ends on two known points to check the position andaimuth at the end of the survey. !he angles at each

point are measured and the distances between

ad"acent points are measured. !he observations can

then be used to compute the positions (latitude and

longitude) of each of the survey points along the line.


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Intersection re#uires

the measurement of

angles by setting up

the theodolite at

control stations andtaking angle

readings by sighting

to the unknown

point(s).

A

B

P = Unknown Point

α

β

Intersection


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Resection

In this method, the

theodolite is set up

over the unknown

point and angle

readings taken to atleast three control

points. $ecause the

theodolite is only set

up once, it is

considered to give a

less secure fix fromthe point of view of

checks and accuracy.

A B

!

P = "nknownoint

α β

$% $&

'


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TRAVERSE

Open Traverse Closed Traverse

!raverse networks have many advantages of

other systems,

including% &ess reconnaissance and organiation

needed

'hile in other systems, which may re#uire

the survey to be performed along a

rigid polygon shape, the traverse can change

to any shape and thus can

accommodate a great deal of different terrains

nly a few observations need to be taken

at each station, whereas in other surveynetworks a great deal of angular and linear

observations need to be made and

considered

!raverse networks are free of the strength

of figure considerations that happen in

triangular systems

cale error does not add up as the traverse

as performed. Aimuth swing errors

can also be reduced by increasing thedistance between stations

!raverse is a method in the field of surveying to establish control networks. It is also used in geodetic work.

!raverse networks involved placing the survey stations along a line or path of travel, and then using thepreviously surveyed points as a base for observing the next point.


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OPEN TRAVERSE

An open traverse starts at

a point of known or

assumed horiontal

position with respect to a

horiontal datum, and

terminates at an unknownhoriontal position. !hus,

open traverses end

without closure. pen

traverses are used on

route surveys, but should

be avoided whenever

possible since they

cannot be properly

checked. *easurements

in open traverses should

be repeated to minimize

mistakes.


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Closed Traverse

A closed traverse is

called starts at a

known or assumed

horiontal position

and terminates at that

point (i.e., loop

traverse), or it starts

at a known horiontal

position and

terminates at another

known horizontal position (i.e.,

connecting

traverses). $oth the

measured

angles and lengths in

a closed traverse maybe checked.

Loop Traverse

LinkTraverse


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Traverse Puroses

!raverse surveys are made for many

purposes to include%

+. !o determine the positions of exiting

boundary markers.

. !o establish the positions of boundary

lines.-. !o determine the area encompassed

within a boundary.

. !o determine the positions of arbitrary

points from which data may be obtained

for preparing various types of maps (i.e.,

establish control for map making).

/. !o establish ground control for

photographic mapping.

0. !o establish control for gathering data

regarding earthwork #uantities in railroad

highway, utility, and other construction

work.

1. !o establish control for locating railroads,highways, and other construction work.


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Traverse Prin!ile

*ust be considered%

+) !he data must be known before (minimum

re#uirements) control points or

+ control point and initial aimuth) !he data must be measured

2istance 3oriontal angle Initial aimuth if it isn4t known before

-) !he data must be computed

Initial aimuth (from control points) 5ext point aimuth 6oordinate point which should be sought7$ 8 7 A 9 d A$sin(: A$)

;$ 8 ; A 9 d A$cos(: A$)


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The data must "e kno#n "efore

6ontrol points can be obtained by

+. !he computation result from previous

measurements eg. >?, traverse,

triangulation, trilateration, resection,

intersection, etc. Assumed yourself locally eg. (@,@), (+@@,+@@)

but only + initial control point

Initial aimuth can be obtained by previous

measurement (data before)


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The data must "e measured

Initial aimuth can be measured by compass 2istance (length of traverse sides) can be

measured by roll meter, theodolite, !, E2* Angle between traverse sides can be

measured by theodolite, !, sextan, compass


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The data must "e !omuted

7$ 8 7 A 9 d A$sin(: A$)

;$ 8 ; A 9 d A$cos(: A$)


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