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 • disseminating a variety of result.

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

History of Surveying 1.

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1.

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Germination About 1400 B.C. The Earth’s Size and Shape 200 B.C. Development of Science of Geometry 120 B.C. Roman Engineer and Surveyor The first century New technologies 18th and 19th century

Importance of Surveying • Map the earth above and below sea level • • •

Prepare navigation charts Establish property boundaries Develop data banks of land-use and natural resource information • Determine facts on the size, shape, gravity, and magnetic fields • Prepare charts of our moon and planets

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 station along the survey route.

Uses for plane surveys 

Land survey



Engineering or Construction Surveys

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Field Mapping

Geodetic Surveys

- Covers distances large enough that

curvature of Earth is significant - Establishes network of precisely located control points

National Geodetic Survey Functions:

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Defines & manages the National Spatial Reference System



Sets standards for geodetic surveys



Maintains a database of U.S. geodetic markers

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 Ground, Aerial, and Satellite surveys

New Technologies for Surveying and Mapping Electronic Total Station Instruments Global Positioning System (GPS) Digital Photogrammetric Systems Land and Geographic Information system (LIS/GIS)

Theodolites •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.

What is Total Station Integrates the functions of a theodolite for measuring angles, and Electronic Distance Meter for measuring distances, digital data and information recording.

USES

Monitoring & Control

Topography Construction Layout

Functions of Total Station 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. Three basic components  Electronic

distance measuring  Electronic angle measuring  Microprocessor

Characteristics of Total Station Instruments 2. Functions Angle:

Horizontal, Vertical, Slope distance

Distance:

Horizontal, vertical, elevation, and coordinates of point Display

the results on a LCD

Functions Performed by TSI  Human-Computer Interactive Design •

Assisting an operator to operate the instrument

•

Prompting by display on LCD

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 11.Communication port

GPS Receivers

Sources of Error in Total Station Work Instrument

Errors

Human

Errors

Natural

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 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

Global Positioning System •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

GPS Global Positioning System (NAVSTAR - DOD)

A network of satellites that continuously transmits coded information, helps to identify precise locations on earth by measuring distance from the satellites

Used for military initially

now heavily used in civilian world

(satellites) Space

User (receivers)

Control (tracking stations)

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 coded radio signal

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 4 satellites at once

Each satellite transmits low power radio signals on several frequencies (L1, L2) Civilian GPS receivers listen on L1 frequency Signal will pass through clouds or glass, but not solid objects (line of sight) no signals in buildings, underwater, caves

Each satellite transmits a unique code Use these coded signals to calculate travel time from the satellite to the GPS receiver Time of Arrival

Ground based Control Stations track the GPS satellites and provide them with corrected orbital and clock (time) information Four unmanned and one master control station

Space Segment Ground stations monitor and update satellite locations

Updated data is transmitted to users

Unmanned stations receive info and send to master Master corrects satellite data and sends uplinks to GPS satellites

How GPS Works… 3

2

1

Accurate (Atomic) Clocks are required

Distance from satellites needs to be known

Need to know Satellite position

4

Correct for atmospheric and ionosphere errors

5

Selective Availability

Ground stations send orbital info to master station Master sends corrected info to satellites

GPS receiver knows location of satellites at all times

When satellite is generating code so is receiver

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 ionosphere

troposphere

Use model to correct

2. Multipath Errors 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.

3. Clock Limitations 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) Inaccuracies in reported position of satellite

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 Scrambling of signal by military

Differential GPS 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

Known base station location

Data corrected in office

Unknown field locations

GPS Error Budget Typical Error in Meters (per satellite)

Satellite clocks Orbital errors Ionosphere Troposhpere Receiver noise Multipath Selective availability*

Standard GPS 1.5 2.5 5.0 0.5 0.3 0.6 30

Differential GPS 0.0 0.0 0.4 0.2 0.3 0.6 0.0

Typical Position Accuracy Horizontal Vertical 3-D

50 78 93 * No longer used

1.3 2.0 2.8

Defining a Location Latitude and Longitude Units of measurement are Degrees Degree is divided into 60 Minutes Minute is divided into 60 Seconds Prime Meridian

equator

Latitude 42° 23’ 50.4” N Longitude 71° 7’ 32.8” W To convert coordinates from degrees, minutes, seconds format to decimal format, use this easy formula: degrees + (minutes/60) + (seconds/3600)

Latitude 42.39733 N Longitude 71.12578 W

THE USE OF GPS RECEIVER FOR THE GEOGRAPHICAL DATA GATHERING

Global Positioning System

Parts of GPS

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 “locked in.”

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 (height).

Important elements of the “Position Page” are: • Elevation (Height) • Lat/Lon • Time (UT)

The “Page” key is used to move from “Status” to “Position” page.

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

CONNECTING GPS TO GIS ENVIRONMENT

Department of Natural Resource (DNR) Garmin Extension in ArcView: Set up

Collect Data

DNR Garmin

ArcView

Getting Connected - Check Turn on Garmin GPS •

• 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.

Getting Connected - Check • Simulator Mode to On

TIP Garmin GPS returns to Simulator Off during power up

Getting Connected - Check • Close VB Program if Open (DNRGarmin operating outside of ArcView)

Getting Connected - Step 1 • Start ArcView – Start Button| Programs | ESRI | ArcView3 | ArcView

• Open an ArcView – New View Or... – “with a new View” when dialog box inquires

Getting Connected - Step 1 • Set View | Properties – Map Units: meters – Distance Units: feet

• Load DNR Garmin Extension – Select File | Extensions... – Scroll to Select “DNR Garmin - ArcView”

– Press OK

Getting Connected - Step 2 • Set Projection – Since some of you may already have loaded DNR Garmin, we need to ensure the Projection is set – Select DNR Garmin | Set Projection

– This may not be the correct projection and datum, Press NO Instructions – Set parameters to the Class

Projections - What’s the big deal anyway! • • • •

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

Projections - What’s the big deal anyway! • 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 in an unprojected View.

projected and is being displayed

Getting Connected - Step 3 • Open DNR Garmin - Select DNR Garmin | Open Garmin GPS

• If GPS is turned on you will see this • Congratulations!

Overview DNR Garmin Menu • • • •

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

DNR Garmin Help • Open DNR Help • Select Help | DNR Help File Index • Select “Downloading Data” from the Contents Tab • Close Help

AUTOMATIC VEHICLE LOCATION

INSAT MSS Reporting Network & Features Suitable where other means of communication are not available easily. Communication from remote field units to pre-assigned destinations.

CBand

Reliable message transfer. Terminals – portable, fixed, mobile

SBand HUB STATION

VMS

Types of Messages • Short message, thin traffic – Position location via GPS – Emergency, SOS type message – Pre-formatted message – Telemetry at large intervals

Message Delivery •From field units to pre-assigned destination – One way messaging – Closed user group service – Meant for agencies, not individuals

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

End to end 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 NMS.

ISD/SITAA/SAC

WEBSERVER www.mss.sac.gov.in/mss.html

DATA

DATA

INSAT - 3C

A DAT

FLEET MANAGEMENT PORTAL

DA TA

HUB STATION

CLIENT

MSS-TERMINAL MOUNTED ON SHIP MSS-TERMINAL MOUNTED ON TRUCK

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 – Mobile satellite phone, VSAT, etc

INSAT MSS Reporting System Features

Wide coverage: Indian Exclusive Economic Zone and beyond Message transmission from anywhere in India EEZ and adjacent seas Monitoring stations located anywhere in India

Vehicle Tracking

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

GPS Positioning Areas

Position of control points (corner of the unit)

Position of control points (centre of the unit)

Creating DEM using digital automatic photogrammetry

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

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

IKNOS Image of Bhat Village

GPS Location of Prominent Places

Nal Sarovar Lake GPS Location Integrated in Arc GIS Environment