l4b-gps - introduction notes
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Global P
ositioning System
GLOBAL
POSTTTONTNG
SYSTEM
(GPS)
1.0 lntroduction
The Global
Positioning System
(GPS)
is a
burgeoning
technology,
which
provides
unequalled
accuracy
and
flexibility of
positioning
for
navigation, mapping,
surveying
and GIS
data capture.
1.1
Why GPS?
.
Trying
to
figure out where
you
are
and
where
you're
going
is
probably
one of
man's
oldest
pastimes.
Figure
1.1:
Helping
you get
from
point
A
to
point
B
Navigation
and positioning are
crucial
to so many activities and yet
the
process
has
always been
quite
cumbersome,
Over
the
years
all
kinds
of technologies
have
tried to
simplify the
task
but
every
one
has had some disadvantage.
Finally,
the U.S.
Department
of
Defense decided
that
they
have
a
super
precise
form
of worldwide
positioning.
r
The
result
is
the
Global Positioning System,
a system
that's
changed
navigation
forever.
1.2
What is GPS?
The
NAVSTAR
(Alavigational
Satellite
7'iming
And
Ranging)
Global
Positioning
System
(GPS)
is a
satellite-based radio
positioning
and
time-transfer
system
designed,
financed,
deployed,
and operated
by
the U.S.
Department
of
Defense.
GPS has also
demonstrated
a
significant benefit
to the civilian community
who are
applying
GPS
to a
rapidly
expanding
number
of applications.
CGT, SUG, FSPU,UiTM ShahAlam
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Global
P
ositioning
System
What attracts
us
to GPS
is:
.
The
relatively
high
positioning
accuracies,
from
tens of meters
down
to the
millimeter
level.
.
The capability of determining
velocity and
time,
to
an accuracy
commensurate
with
position.
o
The signals are available
to
users
anywhere on the
globe:
in
the air,
on
the
ground,
or at
sea.
o
lt a
positioning
system
with no user
charges,
that
simply
requires
the
use
of
relatively
low
cost
hardware.
.
lt
is an
all-weather
system, available
24 hours
a day.
o
The
position
information
is
in
three
dimensions,
that is, vertical
as well as
horizontal
information is
provided.
The number
of
civilian users is already significantly
greater
than that of the military users.
However,
for the time being the U.S. military still operates
several levers
with which
they
control
the
performance
of GPS.
Nevertheless, despite
the
handicap
of GPS
being
a
military
system
there
continues
to
be
tremendous
product
innovation
within
the
clvilian
sector, and
it
is ironic
that this
innovative
drive
is
partly
directed
to developing
technology
and
procedures
to overcome some of
the
constraints
to GPS
performance
which
have
been applied
by
the
system's military
operators.
{.3
GPS
System
configuration
GPS
is
a
space
based radio
positioning
system
that
provides
24
hour
three
dimensional
position,
velocity
and
time
information
to
suitably
equipped users
anywhere
on
the
surface of
the
earth. GPS
involve
three
major
components,
the satellites,
the
ground
based
control
of
the
satellites
and
the
user. These
are
often
referred
to
as the
Space, Control
and
User
Segment.
Figure
1.22 A
constellation
of 24
satellites
CGT, SUG,
FSPU,UiTM
Shah
Alam
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Glob al P ositioning System
ds
Figure
1.3:
GPS System Elements
1.3.1
Space Segment
The
Space Segment of the system consists
of the
GPS satellites
comprising the
satellites
and the transmitted signals. These space
vehicles
(SVs)
send radio
signals
from
space.
Figure 1.5:
Navstar
GPS
Constellation
Name: NAVSTAR
Manufacturer: Rockwell lnternational
Altitude:
10,900 nautical
miles
(20,200
km),
Weight:
1900
lbs
(in
orbit)
Size:
17
ft with
solar
panels extended,
Orbital
Period:
12
hours
Orbital Plane: 55 degrees
to equatorial
plane,
Planned
Lifespan: 7.5
years
CGT, SUG,
FSPU,UiTM
Shah
Alqm
3
GPS Noninsl
Constellation
2*
Satcllites in 6
Orbital
Plancs
4
$atclliter in eaeh Plane
2{1p00
krn .dltitudss,
55
Degrrc
lnclination
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Global
P
ositioning
System
Current constellation:
24
Block
ll
production
satellites
Future satellites:
21 Block
lll
developed by
Martin Marietta.
The nominal
GPS
Operational
Constellation consists of 24
satellites
that
orbit the earth
in
12
hours.
1.3.2
ControlSegment
The Control Segment
consists
of a
system of tracking stations
located around
the
world.
These
ground
facilities carrying out the
task of
satellite tracking,
orbit computations,
telemetry and
supervision
necessary for the daily control of
the
space
segment.
n.?-r,
M
ooitti 's'
igtf
Monitor
Station
t'
a
'wajaleirr
Z*rq.rr,station
L---.{
I
.
Yf
Glabal
Positioning
System
iGFSi
Master
Cantrol
and
Manitor
Station
Network
ipi*eo
Garcia
lVtonitor Station
Figure
1.6:
GPS
Master
Control
and Monitor
Station
Network
Figure
1.7: GPS Control
The Master Control facility is located
at
Falcon Air
Force Base
in
Colorado.
These
monitor
stations measure signals from the SVs which are incorporated
into orbital models
for
each
satellites.
The
models
compute
precise
orbital data
(ephemeris)
and
SV
clock
corrections
for
each satellite.
The Master Control station
uploads
ephemeris
and
clock data to
the
SVs.
The
SVs
then
send subsets
of
the
orbital ephemeris
data
to GPS
receivers
over
radio signals.
1.3.3 User Segment
The
GPS
User Segment
consists
of the GPS receivers and the user
community.
GPS
receivers convert
SV
signals
into
position, velocity, and
time
estimates. Four satellites
are
required
to compute
the four dimensions
of
X, Y, Z
(position)
and Time.
GPS.receivers
are
4
CGT,
SUG, FSPU,U|TM Shqh
Alam
';,//'
,/T,,orooo**
CoNTRoL
STATToN
RECEMR
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Global
P
ositioning
System
used
for navigation,
positioning,
time
dissemination,
and other research.
Navigation in three
dimensions is
the
primary
function
of GPS.
Navigation receivers
are
made
for
aircraft,
ships,
ground
vehicles,
and
for
hand
carrying
by individuals.
Figure 1.8:
Users, GPS Navigation
Precise
positioning
is
possible
using GPS
receivers
at
reference
locations
providing
corrections
and
relative
positioning
data for remote
receivers. Surveying,
geodetic
control,
and
plate
tectonic
studies are examples. Time and frequency
dissemination,
based on
the
precise
clocks on
board the SVs and
controlled
by
the monitor
stations, is
another use for
GPS.
Astronomical
observatories, telecommunications
facilities, and
laboratory
standards
can be set
to
precise
time
signals
or
controlled
to
accurate frequencies by special
purpose
GPS
receivers.
1.4
How
GPS
Works?
Here's how GPS
works
in
five
logical steps:
.
The
basis
of
GPS
is triangulation from satellites.
.
To
triangulate,
a
GPS
receiver measures
distance
using the
travel time
of radio
signals.
.
To measure
travel time, GPS
needs very accurate
timing
which
it
achieves with
some
tricks.
o
Along
with
distance,
you
need
to
know
exactly
where
the
satellites are
in
space.
High
orbits and
careful
monitoring
are the secret.
.
Finally
you
must correct for
any delays the
signal
experiences
as
it travels through
the
atmosphere.
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FSPU,UiTM
Shah
Alam
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Global
P
ositioning
System
1.5
GPS
Applications
GPS
technology
has matured into a
resource
that
goes
far
beyond its
original design
goals.
These
days
scientists, sportsmen, farmers, soldiers,
pilots,
surveyors, hikers,
delivery
drivers,
sailors,
dispatchers,
lumberjacks,
fire-fighters, and
people
from many
other
walks
of
life
are using
GPS
in ways
that
make their work more
productive,
safer,
and sometimes even
easier.
These applications
fall
into
five
broad categories.
o
Location
-
determining
a basic
position
.
Navigation
-
getting
from
one
location
to
another
o
Tracking
-
monitoring
the
movement of
people
and
things
.
Mapping
-
creating
maps
of
the
world
. Timing
- bringing
precise timing to the world
1.5.1
Location
-
determining a basic
position
(q,I,h
)
or
(X,Y,Z)
'Where
am l? The first and most obvious
application
of GPS
is
the
simple determination
of
a
position
or location. GPS is the
first
positioning
system to
offer highly
precise
location
data
for
any
point
on
the
planet,
in
any
weather.
GPS is also being applied
in
countries
to
create exact location
points
for their
nationwide
geodetic
network,
which will be
used
for surveying
projects.
Once
in
place
it
will
support
the
first
implementation
of a nationally created
location
survey
linked
to the WGS-84
global
grid.
For example,
getting
to
the
height
of
a mountain was
tricky,
but
GPS made
it
possible.
1.5.2 Navigation
-
getting
from
one location to
another.
'Where
am I
going?
GPS
helps
you
determine exactly
where
you
are, but
sometimes
important
to
know how to
get
somewhere else. GPS
was
originally
designed
to
provide
navigation information for
ships and
planes.
So
it's
no surprise
that while
this technology is
appropriate
for
navigating on
water,
in
the
air and on
the
land.
6
Figure
1.9: Satellites
are
reference
points
for
location
on earth.
CGT, SUG, FSPU,UiTM ShahAlam
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Global P os itioning System
1.5.3
Tracking
-
monitoring
the movement.
lf
navigation
is
the
process
of
getting
something
from
one
location
to another,
then
tracking
is the
process
of
monitoring
it as
it
moves along.
GPS used
in
conjunction
with
communication
links and
computers
can
provide
the
backbone
for
systems tailored
to
applications in
agriculture,
mass
transit,
urban
delivery,
public
safety,
and
vessel
and vehicle
tracking.
So it's no
surprise
that
police,
ambulance,
and fire
departments
are adopting
systems
like
GPS-based
AVL
(Automatic
Vehicle Location).
Manage
to
pinpoint
both
the
location
of the emergency and the
location
of the
nearest
response
vehicle
on
a computer
map.
With
this
kind
of
clear
visual
picture
of
the situation,
dispatchers
can
react
immediately
and confidently.
W
Figure
1.11: Tracking
1.5.4 Mapping
-
creating
maps of the world.
Using GPS
to survey and
map
it
precisely
saves
time
and
money
in
this
most stringent
of
all
applications. Today, GPS makes it
possible
for a single
surveyor
to
accomplish
in
a day
what
used
to take weeks
with
an entire
team.
And
they can
do
their work
with a
higher level
of
accuracy
than
ever
before. Mapping is the art and science
of
using GPS
to
locate
items,
and
then create maps and
models of
everything
in
the
world.
And we
do mean
everything,
CGT,
SUG,
FSPU,UiTM
Shah
Alam
7
(c)
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Global P ositioning
System
such as:
mountains, rivers,
forests,
landforms,
roads,
routes,
city
streets,
endangered
animals,
precious
minerals,
disasters,
trash, archeological
treasures
and
all sorts
of
resources.
GPS is mapping
the
world.
&dffiS'r*m
F.,*l**fu**
Figure
1.12: Mapping
1.5.5 Bringing
precise
timing
to the world.
GPS
is
also used
to
disseminate
precise
time,
time
intervals,
and
frequency.
Time
is
a
powerful
commodity,
and exact time
is more
powerful
still.
Knowing
that
a
group
of
timed
events
is
perfectly
synchronized is
often very important.
GPS
makes
the
job
of
synchronizing
our
watches
easy and reliable.
There are three fundamental ways
we use time. As
a
universal
marker,
time tells us
when
things happened
or
when
they
will.
As
a
way
to
synchronize
people,
events,
even
other
types of signals,
time
helps keep
the world
on schedule.
And as a way
to tell
how long
things
last,
time
provides an
accurate,
unambiguous sense of duration.
Astronomers,
power
companies, computer networks,
communications
systems, banks,
and
radio
and television stations can
benefit
from
this
precise
timing.
One
investment
banking
firm
uses
GPS
to
guarantee
their
transactions are recorded
simultaneously
at all otfices
around
the
world.
1.6 Methods
of
observations
The
ditferent methods of observations with GPS
include
absolute
positioning,
relative
positioning
in
translocation
mode, relative positioning using differential GPS technique,
and
kinematic GPS surveying technique.
CGT, SUG,
FSPU,UiTM
Shah
Alam
{;{1,
**mrt{rffi
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r#
ryfftn*
Figure
1.13:
Timing
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Global
P ositioning System
1.
Absolute Positioning:
The
pseudo
ranges
(the
satellite antenna
range,
contaminated
by
the
receiver block
bias)
from
minimum
four
satellites are observed
at the
given
epoch, from which
the
four
unknown
parameters
-
the
3D
position
of
the
antenna
(X,
Y,
Z) and the
receiver
clock error
can
be determined. The accuracy of
the
position
obtained from
this
method
depends
upon
the
accuracy of the time and
position
messages
received from
the
satellites.
With the
selective availability operational,
the absolute
positioning
in
realtime
is limited
to about
100 meters,
which
can
be
improved
to
a
few2
meters
level by using
post-processed
satellite
orbit information
in
the
post-processing
mode.
The accuracy
of
absolute
positioning
with GPS is limited
mainly due
to
the
high
orbit
of
the
satellite.
2.
Relative
Positioning:
ln the
translocation
mode with
tow
or more GPS receivers
observing the same
satellites
simultaneously
many common errors, including
the
major effect
of SA
(selective
availability)
get
cancelled out,
yielding
the
relative
positions
of the
two
or
more stations
with
a
very
high
accuracy.
The
length
of
the
base line between
two
stations, and also
the
absolute
position
of
one of
the stations,
if
accurate
position
of
the
other
station
is known, can be obtained
to
cm-level
accuracy,
using carrier phase
observations.
ln
differencing
mode
of
observation,
using
single difference
(difference
of carrier
phase
observations
from
two
receivers
to
the
same satellite),
double
difference
(between
observations from two receivers to
two satellites)
and triple
difference
(difference
of double differences
over
two
time
epochs),
effect
of
many
errors such as
receiver
and satellite clock errors
etc.,
can be minimized.
Use of dual frequency observations
(both
L1 and L2
frequencies)
eliminates
the
major
part
of
ionosphere
effect
on
the
signal,
thus
improving
the
accuracy
of
positioning.
With accurate satellite orbit and
use
of
such refined
procedures
cm-level
accuracy
is
possible
even in regional and
global
scale
surveys.
3.
Differential
GPS:
A
modification
of
the
relative
positioning
method is
the differential
GPS technique,
where
one of
the two
receivers
can
receive
the
messages
given
by this transmitter.
The
transmitting
receiver
is kept
fixed
on a
point
whose
location
is known
to
high
degree of
accuracy.
Based
upon
this
position.
The
receiver
computes
observations
to
the
range/phase observations
from
GPS observations.
Such as
system
is
suited
for
applications
such
as vehicle
guidance
system,
location-fishing
boats
close to
the
seashore, etc.
The
limited range
of
the transmitter restricts
the
use of
such system to
few km.
4.
Kinematic GPS:
ln
the
kinematic GPS
technique,
one
of
the receivers is in
relative
motion with
respect to
the other
receiver having been mounted
either
on a
vehicle or ship or
aircraft. This
technique
has
a
number of important
applications,
including
ship and
aircraft
navigation,
photogrammetric
survey
control
etc.
I
CGT,
SUG,
FSPU,U|TM
Shah
Alam
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Global P
ositioning System
1.7 GPS Reference Systems and Transformation
of
Coordinate.
Normally, regional surveys are conducted with respect
to a
local
datum.
In
Malaysia, the
Modified Everest Ellipsoid
is in
used and
the
satellite
positioning
system
provides
ground
coordinates
of any
point
in
an earth-centered
coordinate
system.
As for
NAVSTAR GPS,
the
worldwide
datum
of
WGS 84
is being used.
ln
order to relate
the
coordinates
determined by
GPS
to the local
geodetic
datum,
the
coordinate transformations
need
to be
done.
The
transformations
which are
often to
be
performed
in
geodetic
computations
are:
o
The
transformation of the ellipsoidal coordinates
(
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Global P ositioning System
Ge*detic
Height,rf
Point P
?oint P
Ellipsoid
Surface
Geodetic
Longitnde
af
Point
P
Figure
1.15:
(9,1,,
h) Coordinate
System
The
geodetic
latitude
(
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Global P ositioning
System
1.7.4
Coordinate Conversion.
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1.8
Conducting GPS Survey
1.8.1
GPS
Survey Equipments
Selection of
the
right
GPS
receiver
for
a
particular project
is critical
to
its success.
1.8.2 Receiverapplications
Land
applications
include
surveying,
geodesy,
resource
mapping,
navigation,
survey
control, boundary
determination, deformation monitoring,
and
transportation.
Marine
applications include navigation
and
positioning
of
hydrographic
surveys.
Airborne
applications include
navigation
and
positioning
of
photogrammetric
based mapping.
1.8.3
Accuracy
requirements
Afirm definition
of the accuracy requirements
(e.9.,
point
accuracy
to
100m,
50m, 25m,
5m,
1m,
cm or mm)
helps
to
further
define
procedure
requirements
(static
or kinematic),
signal
reception requirements
(whether
use
of
C/A- or L1lL2 P-codes
is
appropriate),
and type of
measurement
required
(pseudo-range
or carrier beat
phase
measurements).
CGT, SUG,
FSPU,U|TM
Shah
Alam
12
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7/24/2019 L4b-GPS - Introduction Notes
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Global P ositioning System
1.8.4 Power
requirements.
The
receiver
power
requirements
are an
important
factor
in
the
determination
of
receiver
type.
Receivers currently run on a variety of
power
sources from fuC
to 12-volt car
batteries
or small camcorder
batteries.
A high
end
GPS receiver
can
operate
3
to
4
hr on
a
set of batteries,
whereas a
low
end
may operate
1 to
2
days on
the
same
set.
1.8.5 Cost.
Cost
is
a
major factor
in
determining
the type
of
receiver
the user can
purchase.
Receiver
hardware and software
costs arc a function of
development
costs, High
end
receivers
are
upwards
of
RM
60,000
down
to
a low end receiver
of
RM 1,500.
1.8.6
Processing requirements.
Operational
procedures
required before, during, and after
an observation
session are
very
manufacturer-dependent
and should
be
thought-fully
considered
before
purchase
of a
receiver.
1.9
GPS
Method
of
Observation and
Precision.
1.9.1 Static mode.
Minimum
# of
Sv's: 4
Min.Observation Time:
t
hour
Precision:
Single-freq:
20 mm
+l-2ppm
Dual-freq: 5 mm
+/-
1
ppm
Other
Characteristics:
Best baseline
top related