HORIZONTAL CONTROL - Yola

ENGINEERING SURVEYING (221 BE)

HORIZONTAL CONTROL

Sr Dr. Tan Liat Choon

Email: [email protected]

Mobile: 016-4975551

HORIZONTAL CONTROL� Horizontal control is required for initial survey work (detail

survey) and for setting out

� The simplest form is a traverse - used to find out the

coordinates of control or traverse stationsN

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Grass

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HORIZONTAL CONTROL

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INTRODUCTION TO TRAVERSE

�A polygon of 2D (or 3D) vectors

�Sides are expressed as either polar

coordinates (β, d) or as rectangular coordinate coordinates (β, d) or as rectangular coordinate

differences (∆E, ∆N)

�A traverse must either close on itself or be

measured between points with known

rectangular coordinates

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� The whole area is divided into various transverses for the easy

surveying. Since this method involves division of survey area into

various transverse, it is termed as Transverse Survey

� A transverse is a geometrical figure consisting of more than three

sidessides

� Almost all surveying requires some calculations to reduce

measurements into a more useful form for determining distance,

earthwork volumes, land areas, etc.

� A traverse is a measurement of straight lines to be used as a basis

for the measurement of detail

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�A traverse is a series of consecutive lines

whose lengths and directions have been

determined from field measurements

�Traversing is the act of establishing traverse

station

�A traverse is developed by measuring the

distance and angles between points that

found the boundary of a site6


�There are two basic types of traverses:

o A Closed Traverse begins at a point of known position and returns to its starting point or to another known point. Calculations can be made to check for errors. This method is preferred because the numbers can be confirmedpreferred because the numbers can be confirmed

o A Open Traverse begins at a point of known point which consists of a series of lines that are connected but do not return to either the original starting point or another known point. There is no method to verify that the measurements of the angles and distances are free from errors. Consequently, this is not a desirable survey method

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WHAT IS A TRAVERSE?

• A polygon of 2D (or 3D) vectors

• Sides are expressed as either polar coordinates (β,d) or as

rectangular coordinate differences (∆E,∆N)

• A traverse must either close on itself • A traverse must either close on itself

• Or be measured between points with known rectangular

coordinates

A closedtraverse A traverse between

known points

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APPLICATIONS OF TRAVERSING

• Establishing coordinates for new points

(E,N)known

(E,N)new

(E,N)new

(E,N)known

(E,N)known

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• These new points can then be used as a

framework for mapping existing features

(E,N)known

(E,N)new(E,N)new

(E,N)new

(E,N)new

(E,N)new

(E,N)known

(E,N)known

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• They can also be used as a basis for setting

out new work

(E,N)new

(E,N)new

(E,N)known

(E,N)known

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EQUIPMENT

• Traversing requires :

� An instrument to measure angles (theodolite)

or bearings (magnetic compass)

An instrument to measure distances (EDM or � An instrument to measure distances (EDM or

tape)

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INTRODUCTION TO TRIANGULATION

�Triangulation is a method of surveying in

which the station points are located at the

vertices of a chain or network of triangles. The

angles of the triangles are measured by angles of the triangles are measured by

transits or theodolites and the sides

determined by computation from selected

sides termed base lines. The base lines are

measured directly on the ground.

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�Triangulation permits the selection of sites for

stations and base lines suitable from both

topographic and geometric considerations

�Triangulation is generally used where the area �Triangulation is generally used where the area

surveyed is large and the employment of geodetic

methods desirable. It includes the operations of

observing angles, measuring base lines, their

mathematical processing, the reconnaissance which

precedes these operations, and the astronomic

observations required to establish a geodetic datum

and control the triangulation16


�The selected survey stations are connected

with survey lines in such a way resulting in the

formation of network of triangles. This survey

is useful in surveying larger areas with uneven is useful in surveying larger areas with uneven

site boundaries

�The various formulas of the triangle are used

to determine and area and various dimensions

of the site

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TRANGULATION� Before, distance was measured manually or calculated from

triangulation

� α, β and distance AB are already known

� C can be calculated by using the distance RC or MC

γ

C

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β

γ

αBA

RM

TRANGULATION

RC: Position of C can be calculated using law of sines and law of cosines

Now we can calculate AC and BC

Last step is to calculate RC via

RC = AC . sin α RC = BC . sin β

MC can be calculated using the Pythagorean theorem

MR = AM – RB = (AB/2) – (BC . cos β)

MC =

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INTRODUCTION TO TRILATERATION

�Since the advent of the long range EDM, a

method of surveying, called trilateration, has

been adopted to combined with triangulation

in order to extend horizontal controlin order to extend horizontal control

�Trilateration is based on the trigonometri

proposition that if the three sides (laterals) of

a triangle are known (measured by EDM).

Thus, the three angles can be computed by

formula as triangulation20

INTRODUCTION TO TRILATERATION

γ

C

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βαBA

INTRODUCTION TO GLOBAL

POSITIONING SYSTEM (GPS)

� Satellite-based navigation system

� Network of 24 satellites placed into orbit by the U.S.

Department of Defense (DoD)

� GPS was developed and is operated by the U.S. DoD. � GPS was developed and is operated by the U.S. DoD.

Originally called NAVSTAR (Navigation System with Timing

and Ranging). Before its civilian applications, GPS was

originally intended for military applications to provide all-

weather round-the-clock navigation capabilities for

military ground, sea, and air forces

� 1980s, system available for civilian use

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�GPS works in any weather conditions, anywhere

in the world, 24 hours a day. No subscription

fees or setup charges to use GPS

�Applications – navigation, location �Applications – navigation, location

determination

�Used for cartography, forestry, mineral

exploration, wildlife habitation management,

monitoring the movement of people and things

and bringing precise timing to the world23



� A worldwide MEO satellite navigational system formed by 24

satellites orbiting the earth and their corresponding receivers

on the earth

� Orbit the earth at approximately 12,000 miles above the surface

and make two complete orbits every 24 hoursand make two complete orbits every 24 hours

� Continuously transmit digital radio signals that contain data on

the satellites location and the exact time to the earth-bound

receivers

� Equipped with atomic clocks within a billionth of a second

precision. Based on this information the receivers know how

long it takes for the signal to reach the receiver on earth

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POSITIONING SYSTEM (GPS)�As each signal travels at the speed of light, the

longer it takes the receiver to get the signal, the

farther away the satellite is. By knowing how far

away a satellite is, the receiver knows that it is

located somewhere on the surface of an imaginary located somewhere on the surface of an imaginary

sphere centred at the satellite

�By using three satellites, GPS can calculate the

longitude and latitude of the receiver based on

where the three spheres intersect

�By using four satellites, GPS can also determine

altitude 25



�MEO, medium or middle earth orbit, a

satellite system used in telecommunications

�MEO satellites orbit the earth between �MEO satellites orbit the earth between

1,000 and 22,300 miles above the earth's

surface

�MEOs are mainly used in geographical

positioning systems and are not stationary in

relation to the rotation of the earth

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ELEMENTS OF GPS

� Space Segment

o Consists of a constellation of 24 satellites (and about six

"spares"), each in its own orbit 20200 kilometres above

Earth. Four additional satellites are held in reserve as spares

� Control Segment� Control Segment

o Consists of ground stations (6 of them, located around the

world) that make sure the satellites are working properly.

The master control station at Schriever Air Force Base, near

Colorado Springs, Colorado, runs the system

� Users Segment

o Consists of receivers, which you can hold in your hand or

mount in a vehicle, like your car, stationary27

ELEMENTS OF GPS

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SPACE SEGMENT

(CONSTELLATION OF SATELLITES)� An orbit is one trip in space around Earth for 24 hours satellite

coverage

� The satellites travel in near-circular orbits that have a mean

altitude of 20,200 km above the earth and orbital period of 12

hours to orbit Earthhours to orbit Earth

� Precise atomic clocks are used in the GPS satellites so that it

keeps time to within three nanoseconds - that’s 0.000000003, or

three-billionths, of a second

� Broadcast signals synchronized with those from other satellites

� The signal travels at the speed of light. Even at this speed, the

signal takes a measurable amount of time to reach the receiver29

SPACE SEGMENT

(CONSTELLATION OF SATELLITES)• The difference between the time when the signal is received and

the time when it was sent, multiplied by the speed of light,

enables the receiver to calculate the distance to the satellite

• For more accurate measurement, the GPS navigation signals are

specially designed for GPS receivers to measure the time of specially designed for GPS receivers to measure the time of

arrival and to allow all the satellites to operate on the same

frequency without interfering with each other

• To calculate its precise latitude, longitude, and altitude, the

receiver measures the distance to four separate GPS satellites.

By using four satellites, the receiver calculates both its position

and the time and doesn't need an expensive atomic clock like

those on the satellites30

SPACE SEGMENT

(CONSTELLATION OF SATELLITES)

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CONTROL SEGMENT

(GROUND STATION)

� The GPS control segment consists of twelve monitoring

stations located around the world

� A master control station at Schriever Air Force Base in

Colorado Springs, ColoradoColorado Springs, Colorado

� Six monitor stations: Hawaii and Kwajalein in the Pacific

Ocean; Diego Garcia in the Indian Ocean; Ascension Island in

the Atlantic Ocean; Cape Canaveral, Florida and Colorado

Springs, Colorado

� Four large ground-antenna stations send commands and data

up to the satellites and collect telemetry back from them32

CONTROL SEGMENT

(GROUND STATION)

�The monitor stations track the navigation signals and send their data back to the master control station. There, the controllers determine any adjustments or updates to the navigation signals needed to maintain precise navigation and needed to maintain precise navigation and update the satellites via the ground antennas. To further improve system accuracy, in 2005, the master control station added data from six monitor stations operated by the National Geospatial-Intelligence Agency to the six GPS monitor stations

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USER SEGMENT (RECEIVERS)

�GPS receivers can be carried in your hand

�Installed on aircraft, ships, tanks, submarines, cars,

and trucks

�Stationary

�These receivers detect, decode, and process GPS

satellite signals

�More than 100 different receiver models are already

in use 34


�The typical hand-held receiver is about the size of a

cellular telephone, and the newer models are even

smaller and fit in a wristwatch or a Personal Data

Assistant

�The commercial hand-held units distributed to U.S.

armed forces personnel during the Persian Gulf War

weighed only 28 ounces (less than two pounds).

Since then, basic receiver functions have been

miniaturized onto integrated circuits that weigh

about one ounce35


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SIGNALS� GPS satellites transmit two low power radio signals, designated L1 and L2.

Recently L5

� Civilian GPS uses the L1 frequency of 1575.42 MHz and L2 frequency of

1227.60 MHz in the UHF band

� The signals travel by line of sight, meaning they will pass through clouds, � The signals travel by line of sight, meaning they will pass through clouds,

glass and plastic but will not go through most solid objects such as

buildings and mountains

� A GPS signal contains three different bits of information - a pseudorandom

code, ephemeris data and almanac data

� The pseudorandom code is simply an I.D. code that identifies which

satellite is transmitting information. You can view this number on your

GPS unit's satellite page, as it identifies which satellites it's receiving

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SIGNALS

�Ephemeris data tells the GPS receiver where each GPS satellite should be at any time throughout the day. Each satellite transmits ephemeris data showing the orbital information for that satellite and for every other satellite in the systemand for every other satellite in the system

�Almanac data, which is constantly transmitted by each satellite, contains important information about the status of the satellite (healthy or unhealthy), current date and time. This part of the signal is essential for determining a position

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SOURCES OF ERROR IN GPSFactors that can degrade the GPS signal and thus affect accuracy include the following:

o Ionosphere and troposphere delays — The satellite signal slows as it passes through the atmosphere. The GPS system uses a built-in model that calculates an average amount of delay to partially correct for this type of error

o Signal multipath — This occurs when the GPS signal is reflected off objects such as tall buildings or large rock surfaces before it reaches the receiver. This increases the travel time of the signal, thereby causing errors

o Receiver clock errors — A receiver's built-in clock is not as accurate as the atomic clocks onboard the GPS satellites. Therefore, it may have very slight timing errors

o Orbital errors — Also known as ephemeris errors, these are inaccuracies of the satellite's reported location

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SOURCES OF ERROR IN GPSo Number of satellites visible — The more satellites a GPS receiver

can "see," the better the accuracy. Buildings, terrain, electronic interference, or sometimes even dense foliage can block signal reception, causing position errors or possibly no position reading at all. GPS units typically will not work indoors, underwater or underground

o Satellite geometry/shading — This refers to the relative position of o Satellite geometry/shading — This refers to the relative position of the satellites at any given time. Ideal satellite geometry exists when the satellites are located at wide angles relative to each other. Poor geometry results when the satellites are located in a line or in a tight grouping

o Intentional degradation of the satellite signal — Selective Availability (SA) is an intentional degradation of the signal once imposed by the U.S. Department of Defense. SA was intended to prevent military adversaries from using the highly accurate GPS signals. The government turned off SA in May 2000, which significantly improved the accuracy of civilian GPS receivers

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HOW DOES GPS WORKS� The principle behind GPS is the measurement of distance (or

“range”) between the satellites and the receiver

� The satellites tell us exactly where they are in their orbits by

broadcasting data the receiver uses to compute their

positionspositions

� It works something like this: o If we know our exact distance from a satellite in space, we know we are somewhere on

the surface of an imaginary sphere with a radius equal to the distance to the satellite

radius

o If we know our exact distance from two satellites, we know that we are located

somewhere on the line where the two spheres intersect

o And, if we take a third and a fourth measurement from two more satellites, we can find

our location. The GPS receiver processes the satellite range measurements and produces

its position 42

HOW DOES GPS WORKS

� GPS uses a system of coordinates called WGS 84, which stands

for World Geodetic System 1984

� It allows surveyors all around the world to produce maps like

the ones you see in school, all with a common reference the ones you see in school, all with a common reference

frame for the lines of latitude and longitude that locate places

and things

� Likewise, GPS uses time from the United States Naval

Observatory in Washington, D.C., to synchronize all the timing

elements of the GPS system, much like Harrison's

chronometer was synchronized to the time at Greenwich

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HOW DOES GPS WORKS

Now you should have a fairly clear picture of the

GPS system:

o You know that it consists of satellites whose paths o You know that it consists of satellites whose paths

are monitored by ground stations

o Each satellite generates radio signals that allow a

receiver to estimate the satellite location and

distance between the satellite and the receiver

o The receiver uses the measurements to calculate

where on or above Earth the user is located44

USES OF GPS

For Military

o GPS system has already proved to be a valuable aid to U.S. military forces

o With GPS the soldiers were able to go places and manoeuvre in

sandstorms or at night. More than 1,000 portable commercial receivers sandstorms or at night. More than 1,000 portable commercial receivers

were initially purchased for their use

o The demand was so great that before the end of the conflict, more than

9,000 commercial receivers were in use in the Gulf region. They were

carried by soldiers on the ground and were attached to vehicles,

helicopters, and aircraft instrument panels

o Navy ships used them for rendezvous, minesweeping, and aircraft

operations 45

USES OF GPS

For Civilians

o GPS is helping to save lives and property across the nation.

Example:

o In 2002, it enabled rescuers to drill a shaft to free trapped miners in Somerset

o Many police, fire, and emergency medical-service units use GPS receivers to determine the police car, fire truck, or ambulance nearest to an emergency, enabling the quickest possible response in life-or-death situations

o GPS-equipped aircraft can quickly plot the perimeter of a forest fire so fire supervisors can produce updated maps in the field and send fire fighters safely to key hot spots

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USES OF GPS

For Constructions

o Mapping, construction, and surveying companies use GPS extensively

o During construction of the tunnel under the English Channel, British and

French crews started digging from opposite ends: one from Dover,

England, and one from Calais, France. They relied on GPS receivers outside England, and one from Calais, France. They relied on GPS receivers outside

the tunnel to check their positions along the way and to make sure they

met exactly in the middle. Otherwise, the tunnel might have been crooked

Example :

o GPS allows mine operators to navigate mining equipment safely, even

when visibility is obscured

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USES OF GPS

�GPS-equipped fleet vehicles, public transportation

systems, delivery trucks, and courier services use

receivers to monitor their locations at all times for

both efficiency and driver safety

�Automobile manufacturers are offering moving-map

displays guided by GPS receivers as an option on new

vehicles. The displays can be removed and taken into

a home to plan a trip. Several major rental car

companies have GPS-equipped vehicles that give

directions to drivers on display screens and through

synthesized voice instructions48

USES OF GPS

�GPS-equipped balloons monitor holes in the ozone layer over the polar regions as well as air quality across the nation

�Buoys tracking major oil spills transmit data using �Buoys tracking major oil spills transmit data using GPS to guide cleanup operations

�Archaeologists, biologists, and explorers are using the system to locate ancient ruins, migrating animal herds, and endangered species such as manatees, snow leopards, and giant pandas

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T H A N K Y O U T H A N K Y O U

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Q U E S T I O N A N D A N S W E RQ U E S T I O N A N D A N S W E RQ U E S T I O N A N D A N S W E RQ U E S T I O N A N D A N S W E R

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HORIZONTAL CONTROL - Yola

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