9.

❖ Space Utilization: GIS helps managers to organize and spatially visualize space and how it can best
be used. Operational costs can be decreased by more efficiently using space including managing the
moves of personal and assets as well as the storage materials. The 3D visualization in GIS platforms
helps planers to create a feeling of experience like virtual walk inside the building and rooms before
construction.

10. ❖ Development of Public Infrastructure Facilities: GIS has many uses and advantages in the field of
facility management. GIS can be used by facility managers for space management, visualization and
planning, emergency and disaster planning and response. It can be used throughout the life cycle of a
facility from deciding where to build to space planning. Also it provides facilitate better planning and
analysis.

11. ❖ Location Identification: This technique is used to find a location for a new retail outlet. It helps to
find out what exists at a particular location. A location can be described in many ways, using, for
instance, name of place, post code, or geographic reference such as longitude or latitude or X/Y.

12. ❖ River Crossing Site Selection for Bridges: The important geotechnical consideration is the stability
of slope leading down to and up from the water crossing. It is advisable to collect historical data on
erosion and sedimentation. On the basis of these information asses the amount of river channel
contraction, degree of curvature of river bend, nature of bed and bank materials including the flood flow
and the flow depth, all these can be done in GIS within estimated time and accurately. This information
has been often used for river crossing site selection for bridges.

13. ❖ Regional Planning: Every day, planners use Geographic Information System (GIS) technology to
research, develop, implement, and monitor the progress of their plans. GIS provides planners, surveyors,
and engineers with the tools they need to design and map their neighborhoods and cities. Planners have
the technical expertise, political savvy, and fiscal understanding to transform a vision of tomorrow into a
strategic action plan for today, and they use GIS to facilitate the decision-making process. (ESRI, GIS
Solutions for Urban and Regional Planning).

4.3 GLOBAL NAVIGATION SATELLITE SYSTEM (GNSS)

Concept of GNSS

Global Navigation Satellite System (GNSS) refers to a constellation of satellites providing signals
from space that transmit positioning and timing data to GNSS receivers. The receivers then use this
data to determine location. By definition, GNSS provides global coverage. Examples of GNSS
include Europe’s Galileo, the USA’s NAVSTAR Global Positioning System (GPS), Russia’s

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Global'naya Navigatsionnaya Sputnikovaya Sistema (GLONASS) and China’s BeiDou Navigation
Satellite System. GNSS (Global Navigation Satellite System) is a satellite system that is used to
pinpoint the geographic location of a user's receiver anywhere in the world. Two GNSS systems are
currently in operation: the United States' Global Positioning System (GPS) and the Russian
Federation's Global Orbiting Navigation Satellite System (GLONASS).

Component of GNSS

The GNSS consist of three main satellite technologies: consists mainly of three segments: (a) space
segment, (b) control segment and (c) user segment. These segments are almost similar in the three
satellite technologies, which are all together make up the GNSS.

Space Segment

The space segment consists of GNSS satellites, orbiting about 20,000 km above the earth. Each GNSS
has its own “constellation” of satellites, arranged in orbits to provide the desired coverage. Each
satellite in a GNSS constellation broadcasts a signal that identifies it and provides its time, orbit and
status. To illustrate, consider the following. You are downtown. You call a friend. Your friend is not
at home, so you leave a message.

Control Segment

The control segment comprises a ground-based network of master control stations, data uploading
stations and monitor stations; in the case of GPS, two master control stations (one primary and one
backup), four data uploading stations and 16 monitor stations, located throughout the world.

In each GNSS system, the master control station adjusts the satellites’ orbit parameters and onboard
high-precision clocks when necessary to maintain accuracy.

Monitor stations, usually installed over a broad geographic area, monitor the satellites’ signals and
status, and relay this information to the master control station. The master control station analyses the
signals then transmits orbit and time corrections to the satellites through data uploading stations.

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 GNSS Segments.

User Segment

The user segment consists of equipment that processes the received signals from the GNSS satellites
and uses them to derive and apply location and time information. The equipment ranges from smart
phones and handheld receivers used by hikers, to sophisticated, specialized receivers used for high
end survey and mapping applications.

Types of GNSS:

The GNSS consist of three main satellite technologies: GPS, GLONASS and Galileo. Each of them
consists mainly of three segments: (a) space segment, (b) control segment and (c) user segment. These
segments are almost similar in the three satellite technologies, which are all together make up the
GNSS. These are as follows.

A. G.P.S.

As of today, the complete satellite technology is the GPS technology and most of the existing
worldwide applications related to the GPS technology. The GNSS technology will become clearer
after the operation of Galileo and the reconstruction of Glonass in the next fe years. The United States
Department of Defense (DoD) has developed the Navstar GPS, which is an all-weather, space based
navigation system to meet the needs of the USA military forces and accurately determine their
position, velocity, and time in a common reference system, any where on or near the Earth on a
continuous basis.

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GPS comprises three main components:

Space segment: The Space Segment of the system consists of the GPS satellites. These space
vehicles (SVs) send radio signals from space as shown in Figure.

1. Control segment:

The Control Segment consists of a system of tracking stations located around the world. The
Master Control facility is located at Schriever Air Force Base (formerly Falcon AFB) in the
State of Colorado, USA.

2. User segment:

The GPS User Segment consists of the GPS receivers and the user community. GPS receivers
convert space vehicle (SV) signals into position, velocity, and time estimates.

GPS Constellation and GPS Satellite Signals.

3. GALILEO:

Galileo segments are almost similar to GPS, but with some modification. The main extension of
Galileo compared to GPS is the implementation of a global/ regional segment for integrity
monitoring.

4. Space Segment

The space segment or the constellation features consists of 30 Medium Earth Orbiting (MEO)
satellites (27 and 3 active spare satellite), distributed evenly and regularly over three orbit planes. The
projected altitude is slightly larger than for GPS 23,616 km and the inclination is 56°.

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5. Ground Segment

The Galileo ground segment is responsible for managing the constellation of navigation satellites,
controlling core functions of the navigation mission such as orbit determination of satellites, and clock
synchronization, and determining and disseminating (via the MEO satellites) the integrity
information, such as the warning alerts within time-to-alarm requirements, at global level. The Global
ground segment will also provide interfaces with service centers. The Ground Control Segment will
consist of about 12-15 reference stations, 5 up-link stations and two control centers. The ground
segment also will include 16-20 monitor stations, three up-link stations for integrity data and two
central stations for integrity computations.

Galileo Segments.

User Segment:

The user segment consists of different types of user receivers, with different capabilities related to the
different GALILEO signals in order to fulfill the various GALILEO services.

Observation Techniques

The basic concept of GNSS is to measure the signal travelling time between artificial satellite and
receiver. By multiplying this time by the light velocity (c), we get the range between the satellite and
the receiver. The time or phase measurement performed by the receiver is based on the comparison
between the received signal at the antenna of the receiver and the generated reference signal by the
receiver. The two signals are affected by the clocks errors. Therefore, the range measured is not true
and it is called pseudo range. Since the signal travels through the atmospheric layers, further noise
should be modelled in order to compute the precise range.

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