Global Positioning System

GLOBAL POSITIONING SYSTEM

Prof. Anjana Vyas School of Planning, CEPT University Ahmedabad 9825522844

What is Surveying

Surveying has traditionally been defined as the science, art, and technology of determining the relative positions of points above, on, or beneath the earth’s surface.

Surveying can be regarded as that discipline which encompasses all methods for

•measuring and collecting information about the physical earth and environment,

•processing that information, and

Surveying activities involve on, above, or below the surface of the land or the sea

History of Surveying

1. The Earth’s Size and ShapeThe Earth’s Size and Shape

200 B.C200 B.C..

1.

1. Development of Science of GeometryDevelopment of Science of Geometry

120 B.C.

120 B.C. 1.

1. Roman Engineer and SurveyorRoman Engineer and Surveyor

The first centuryThe first century 1.

1. New technologiesNew technologies

Importance of Surveying

•

• Prepare navigation chartsPrepare navigation charts

• Establish property boundaries Establish property boundaries

• Develop data banks of land-use andDevelop data banks of land-use and

natural resource information natural resource information

• Determine facts on the size, shape, gravity, Determine facts on the size, shape, gravity,

and magnetic fieldsand magnetic fields

Classification of Surveying

Plane Surveys

•

_{Plane Survey instruments are very}

simple:

•

_{Consisting of a plane table,}

•

A small drawing table mounted on a

tripod

•

A table can be leveled and rotated.

Plane Surveys

•The locations of lines and points are plotted directly on the drawing paper.

•_{Setting up the table must be leveled}

•it is oriented correctly with a reference meridian (e.g. north line).

•_{The table is moved and re-oriented at each}

Uses for plane surveys

 Land survey  Engineering or

Construction Surveys

Geodetic Surveys

-

Covers distances large enough that

curvature of Earth is significant

-

Establishes network of precisely

located

control points

National Geodetic Survey

Functions:



Reference System





Specialized Types of Surveys

Control surveys

Topographic surveys

Land, Boundary, and Cadastral surveys Hydrographics surveys Route surveys built surveys Mine surveys Solar surveys Optical tooling

New Technologies for Surveying and

Mapping

Electronic Total Station Instruments

Global Positioning System (GPS)

Digital Photogrammetric Systems

Land and Geographic Information

system

•

Measures horizontal angles like the plane

table,

•

calculate vertical angles,

from which elevations could be derived.

Theodolites are lighter

They do not require the construction of the

hardcopy map in the field.

Integrates the functions of a

theodolite

for measuring angles,

and

Electronic Distance Meter

for measuring

distances,

digital data and

information recording.

Topography Construction Layout Monitoring & Control

USES



Measure angle and distance

accurately and quickly



Make computation with

angle and distance



Display the results in

real time

Widely used for topographic,

hydrographic, cadastral, and

construction

surveying

Characteristics of Total Station

Instruments

1.

1.

Three basic components

Three basic components



Electronic

distance

measuring

Electronic

angle

measuring

2.

2.

Functions

Functions

Angle: Horizontal, Vertical, Slope distance Distance: Horizontal, vertical, elevation,

and coordinates of point

Display the results on a LCD

Characteristics of Total Station

Instruments

Functions Performed by TSI

 _{Human-Computer Interactive Design} • Assisting an operator to operate the

instrument

Parts of A TSI

1.Telescopes:

2.Angle measurement system

3.Vertical circle

4.Rotation of the telescope

5.Tri-branch

6.Bases of total stations

7.Optical plummet

8.Tripods

9.Microprocessor

10.Keyboard and display

Sources of Error in

Total Station Work



Instrument Errors

Instrument Errors

Human Errors

Human Errors

Instrument Errors

Instrument Errors

Instrumental errors are caused by imperfections in

the design, construction, and adjustment of instruments and other equipment

Imperfect linear or angular scales.

Instrument axes are not perfectly parallel or perpendicular to each other.

Misalignment of various part of the instrument. Optical distortions causing “what you see is not exactly what you are supposed to see”.

Instrumental errors are eliminated by

• Using proper procedures, such as observing angles in direct and reverse modes

• Balancing foresights and back sights and repeating measurements

• Periodically checked, tested and adjusted (or calibration)

Human errors are caused by the physical limitations of the human senses of sight and touch, e.g. error in the measured value of a horizontal angle, caused by the inability to hold a range pole perfectly in the direction of the plumb line.

Error can be minimized by Common sense

Self-calibration (estimating personal errors by experiments and experience)

Attention to proper procedures

Natural Errors

Natural errors result from natural physical conditions such as atmospheric pressure, temperature, humidity, gravity, wind, and atmospheric refraction

Natural errors are mostly systematic and should be corrected or modeled in the adjustment.

Some natural errors such as the effect of curvature can be eliminated by a procedure.

The leveling procedure to eliminate curvature corrections is to average foresights and backsights

Applications of

GPS

•24 satellites

orbiting earth in

12

hours

•Constellation provides

5 to 8

visible satellites

from any

point on the earth

•4 satellites

are required to

compute the 3 dimensions of

position

•Precision ranges from 10 m

to 100 m

A

network of satellites

that continuously transmits

coded information, helps to identify

precise

locations

on earth by measuring

distance from the satellites

GPS

Global Positioning System

Used for

military initially

now heavily

(satellites)

(tracking stations)

(receivers)

Space

The first GPS satellite

was launched in 1978

constellation of

24

satellites

since 1994

each satellite is built

to last about 10 years

2,000 pounds weight,

17 feet long solar panels

powered by solar energy

continuously broadcast

High orbit satellites

(about 12,000 miles

above earth surface)

Speed 7,000 miles per hr.

allows them to circle earth

once every

12 hours

Arranged in orbit

so as to provide

coverage by

Each satellite transmits

low power radio signals

on several frequencies (L1, L2)

Civilian GPS receivers

listen on L1 frequency

no

signals

in buildings, underwater, caves

Signal will pass through clouds or glass,

but not solid objects

(line of sight)

Each satellite transmits a unique code

Use these coded signals to calculate

travel time from the satellite to the GPS receiver

Ground based Control Stations track the GPS

satellites and provide them with corrected

orbital and clock (time) information

Four unmanned and

Unmanned stations receive info and send to master

Master corrects satellite data and

sends uplinks to GPS satellites

Updated data

is transmitted to users Ground stations

monitor and update satellite locations

How GPS Works…

1 Distance from_{satellites needs}

to be known

4 Correct for atmospheric_{and ionosphere errors} 3 Need to know_{Satellite position}

2 Accurate_(Atomic)

Clocks are required

GPS receiver knows location of satellites at all times

Master sends corrected info to satellites

Ground stations send

Receiver compares the two codes to determine how much it needs to

shift (delay) its code to match the satellite code

Uses measurements from 4+ satellites distance = travel time x speed of light

Sources of Error

1. Atmospheric Interference

signal slows as it passes through atmosphere

Use model to correct

troposphere

Multipath

means that the same radio signal is

received several times through different paths.

For instance, a radio wave could leave a satellite

and travel directly to the receiver, but it also

bounces off a building and arrives at the receiver

at a later time.

The internal satellite and receiver clocks have

limited accuracy, and they are not precisely

synchronized. Since

position

computations are

highly dependent on

accurate timing

information,

small clock errors can cause significant errors in

position computations.

4. Ephemeris Error (Orbital errors)

5. Satellite Configuration

if all of the visible satellites happen to be

bunched close together, the triangulated position

will be less accurate than if those same satellites

were evenly distributed around the visible sky.

6. Selected Availability

Place a GPS receiver (reference or base station) at a known location. This base station receiver will calculate receiver

errors by comparing its actual location to the location

computed from the signals. This error information is sent to the rover receiver, which uses it to correct the position information it computes from the signals. Accuracies of DGPS systems can range from 15 feet to 3 feet depending

on system configuration.

Differential GPS in Action

1. Compares field data to data

collected at the same time at

a nearby base station

2.

Error

at base station known

and

subtracted

from field data

GPS Error Budget

Typical Error in Meters (per satellite)

Standard GPS Differential GPS Satellite clocks 1.5 0.0 Orbital errors 2.5 0.0 Ionosphere 5.0 0.4 Troposhpere 0.5 0.2 Receiver noise 0.3 0.3 Multipath 0.6 0.6 Selective availability* 30 0.0 Typical Position Accuracy

Horizontal 50 1.3

Vertical 78 2.0

3-D 93 2.8

Latitude and Longitude

Defining a Location

Units of measurement are Degrees

equator Prime

Meridian

Degree is divided into 60 Minutes Minute is divided into 60 Seconds

To convert coordinates from

degrees, minutes, seconds format

to decimal format, use this easy formula:

degrees + (minutes/60) + (seconds/3600)

Latitude

42° 23’ 50.4” N

Longitude

71° 7’ 32.8” W

Latitude

42.39733 N

THE USE OF GPS

THE USE OF GPS

RECEIVER FOR THE

RECEIVER FOR THE

GEOGRAPHICAL DATA

GEOGRAPHICAL DATA

GATHERING

Global Positioning

System

Garmin

GPS Unit –

as seen

Immediately After

Power is Turned On

As Satellites

are linked,

their Positions in

the Sky, and the

Strength of their

Signals are Displayed.

Gray signal bars Not to be

When 4 Satellites have

been “locked in”,

GPS can determine

Coordinates.

Signal strength bars turn black.

If number of satellites

is not sufficient,

or if “geometry” is

poor,

“2D Navigation”

message appears.

This means that elevation

(height)

measurements are

not to be used.

“3D Navigation”

message means

that conditions

are acceptable for

determining

elevation

Important elements

of the “Position Page”

are:

• Elevation (Height)

• Lat/Lon

The “Page” key is used to move from “Status” to

“Position” page.

The “Quit” key is used to move from “Position” page

CONNECTING GPS TO GIS

CONNECTING GPS TO GIS

ENVIRONMENT

Department of Natural Resource (DNR) Garmin

Extension in ArcView: Set up

Collect Data

ArcView DNR Garmin

Getting Connected - Check

• For best results, the Garmin GPS should be connected to the computer via a serial cable and turned on before loading the DNR Garmin extension.

•

Turn on

• Simulator Mode to On

Getting Connected - Check

Getting Connected - Check

• Close VB Program if Open (DNRGarmin operating

outside of ArcView)

Getting Connected - Step 1

• Open an ArcView

– New View Or...

– “with a new View” when dialog box inquires

• Start ArcView

Getting Connected - Step 1

• Set View | Properties

– Map Units: meters

– Distance Units: feet

• Load DNR Garmin

Extension

– Select File | Extensions...

– Scroll to Select

Getting Connected - Step 2

– This may notnot be the correct projection and datum, Press NO – Set parameters to the Class Instructions

• Set Projection

– Since some of you may already have loaded DNR

Garmin, we need to ensure the Projection is set

• To GIS personnel - this is a big deal

• Intimately linked to the data collection from the field • Ask how the GIS personnel prefers the data

• All raw GPS data is expressed in Lat/Long Decimal Degrees - WGS84 Datum

– Setting Garmin to Garmin Protocol ensures data arriving in downloaded as DD WGS84

• When GPS data is downloaded to ArcView the data is projected “on the fly” using the projection you define using:

– DNRGarmin | Set Projection Dialog box

– Information is stored in a file and can be reset at any time

• This assumes the base data is projected and is being displayed in an unprojected View.

Getting Connected - Step 3

• If GPS is turned on you will see this

• Congratulations!

• Open DNR Garmin - Select DNR Garmin | Open

Garmin GPS

• OPEN Garmin GPS

:

Starts the DNR Garmin Program

• Set Projection

:

Sets the Projection for Incoming Data

• Convert Points

:

Convert Point shapefile to line or polygon

• Calculate Shape Attributes

:

Calculates attributes of

shapefile (GIS units) and adds them to the attribute table.

• Add Documentation

• Calculate CEP

:

Calculates Circular Error Probability for

the Selected Point Theme

• Open DNR Help

• Select Help | DNR Help File

Index

• Select “Downloading Data”

from the Contents Tab

• Close Help

HUB STATION C- Band VMS

INSAT MSS Reporting

INSAT MSS Reporting

Network & Features

Network & Features

S- Band

Suitable where other means of

communication are not available easily.

Communication from remote field units to pre-assigned destinations.

Reliable message transfer.

Types of

Messages

• Short message, thin traffic

– Position location via GPS

– Emergency, SOS type message

– Pre-formatted message

– Telemetry at large intervals

Message Delivery

– One way messaging

– Closed user group service

– Meant for agencies, not individuals

•From field units to pre-assigned destination

Messaging Reliability

Reliable message transfer

Multiple transmission of same message on satellite link Messages stored at hub

Delivery from hub to customer through internet Message archival facility at hub

Message

Security

encryption. Terminal authentication checked by NMS

for authorisation.

Delivery over VPN.

NMS software is fully protected from unauthorised access. Messages cannot be tapped at the

WEBSERVER www.mss.sac.gov.in/mss.html HUB STATION INSAT - 3C MSS-TERMINAL MOUNTED ON SHIP CLIENT ISD/SITAA/SAC MSS-TERMINAL MOUNTED ON TRUCK DA TA D A T A DATA DATA

System - USP

• No other means of communications

exist:

– Deserts, seas, mountains, remote

areas

• Existing means unsatisfactory:

– Unreliable telecom links

– Unacceptable delays

• Existing means costly and difficult

INSAT MSS Reporting System

Features

Wide coverage:

Indian Exclusive Economic Zone and beyond

Message transmission from anywhere in India EEZ and adjacent seas

View exceptions based on speed, zone entry/exit, idle time, excessive stop time, auxiliary activation, etc.

Disaster Management

Proven technology in many disaster situations such as

Hurricane Andrew, USA Kobe Earthquake, Japan

San Francisco Earthquake, USA US Forest Service Wildland Fires 1994 Mississippi Floods, USA

Government

•Local/Regional Governments •Public Works/Utilities

•Planning/Development •Public Safety

•Land Information Systems •Environmental Quality

City model without texture based on RS, GPS height readings and GIS

City modeling (texture) Based on RS, GPS height reading and GIS

Nal Sarovar Lake GPS Location Integrated in Arc GIS Environment