GPS BASICSGPS BASICSv.1.6v.1.6

LCdr. Ronaldo C. GatchalianLCdr. Ronaldo C. GatchalianChief GGD-MGD, NAMRIAChief GGD-MGD, NAMRIA

OUTLINEOUTLINE

WHAT IS GPSWHAT IS GPS METHODS OF OBTAINING POSITIONMETHODS OF OBTAINING POSITION COORDINATE SYSTEMSCOORDINATE SYSTEMS PRS 92PRS 92 SURVEYING WITH GPSSURVEYING WITH GPS

WHAT IS GPS?WHAT IS GPS?

WHAT DOES IT DO?WHAT DOES IT DO?

GPS --Shortened form of NAVSTAR GPS. GPS --Shortened form of NAVSTAR GPS. NAVNAVigation igation SSystem with ystem with TTime ime AAnd nd RRanginganging GGlobal lobal

PPositioning ositioning SSystem.ystem. --It is a solution for one of man’s oldest and --It is a solution for one of man’s oldest and

most troublesome problem most troublesome problem --Provides an answer to the question “where --Provides an answer to the question “where

on earth am I?”on earth am I?”

Where on earth am i?

After WWII it became apparent to U.S. DoD that a After WWII it became apparent to U.S. DoD that a solution had to be found to the problem of solution had to be found to the problem of accurate, accurate, absolute positioningabsolute positioning..

Several projects and experiments ran during the next Several projects and experiments ran during the next 25 years, including:25 years, including:

-- Transit, Loran, Decca etc. -- Transit, Loran, Decca etc. -- All of these projects -- All of these projects allowed positions to be allowed positions to be

determineddetermined but were limited in accuracy or but were limited in accuracy or functionality.functionality.

During the 70s, GPS project was proposedDuring the 70s, GPS project was proposed -- This concept promised to fulfill all the requirements of -- This concept promised to fulfill all the requirements of

the U.S. Govt. i.e. to be able to: the U.S. Govt. i.e. to be able to: -- Determine ones position accurately-- Determine ones position accurately -- at any point on the earth’s surface-- at any point on the earth’s surface -- at any time-- at any time -- in any weather. -- in any weather.

GPSGPS

GPS is a satellite-based system that uses a constellation GPS is a satellite-based system that uses a constellation of 24 satellites to give a user an of 24 satellites to give a user an accurate position.accurate position.

Accuracy is: hiker or soldier—15m; A ship in coastal Accuracy is: hiker or soldier—15m; A ship in coastal waters– 5m; land surveyor– 1cm or less.waters– 5m; land surveyor– 1cm or less.

GPS can be used to achieve these GPS can be used to achieve these accuraciesaccuracies in all of in all of these applications, the difference being:these applications, the difference being:

-- -- type of GPS receiver usedtype of GPS receiver used -- technique employed -- technique employed GPS was GPS was originally designed for military useoriginally designed for military use . Soon after . Soon after

the original proposals were made, it became clear that the original proposals were made, it became clear that civilians could also use GPS, not only for personal civilians could also use GPS, not only for personal positioning but for marine and surveying as well. positioning but for marine and surveying as well. Applications range from in-car navigation to scientific Applications range from in-car navigation to scientific research.research.

OOSA Training Course

Can be this: an instrumented sheep... Can be this: an instrumented sheep...

Specimen used for scientific applications: collection of grass samples in remote access areas.

OOSA Training Course

…… …… or a handy parking locator.or a handy parking locator.

you can parkhere

OOSA Training Course

Already an important realityAlready an important realityGPS on Cell PhoneGPS on Cell Phone

- 5 millions already in Japan -

OOSA Training Course

The World of Applications The World of Applications (GJU source(GJU source))

Safety of Life Mass Market Professional

Aviation Rail Maritime Inland waterways Ambulance Police / Fire Search and Rescue Personal Protection Traffic surveillance Dangerous goods trans. ADAS

Personal communication and navigation

Cars / motorcycles Trucks & buses Light Commercial

Vehicles Personal outdoor

recreation Others…

Oil and Gas Mining Timing Environment Fleet Management Asset Management Geodesy Meteorological

forecasting Land Survey Precision survey Precision Agriculture Fisheries Vehicle control and

robotics Construction / Civil

Engineering Space

Integrity (error-free),Standards,Regulation,Continuity,Availability,Accuracy

Low costs,Low power cons.,

Small size,Friendly use,Best perf. accordingly

High precision,High accuracy,High reliability

Types Of GPS ReceiverTypes Of GPS Receiver Handheld- small light weight (like cell phones), single Handheld- small light weight (like cell phones), single

frequency, used by a hiker or a soldier. Good for searching frequency, used by a hiker or a soldier. Good for searching people and places. Accuracy =+/-15m with S.A. offpeople and places. Accuracy =+/-15m with S.A. off

Marine – bigger than handhelds, usually single frequency, Marine – bigger than handhelds, usually single frequency, can be on natural or differential mode, used by ships in can be on natural or differential mode, used by ships in high seas and coastal waters. Good for positioning depths high seas and coastal waters. Good for positioning depths in hydrographic surveys. Accuracy = +/- 15m (Natural) or in hydrographic surveys. Accuracy = +/- 15m (Natural) or +/- 0.50m (Diff’l)+/- 0.50m (Diff’l)

Geodetic – can be as small as handhelds, single, dual or Geodetic – can be as small as handhelds, single, dual or multi- frequency (GNSS), used by land surveyors. Good for multi- frequency (GNSS), used by land surveyors. Good for positioning geodetic control points.positioning geodetic control points.

Accuracy = +/- 5 to 15m(autonomous)Accuracy = +/- 5 to 15m(autonomous) = +/-5 to50cm (PPK,RTK)= +/-5 to50cm (PPK,RTK) = millimeter (Post processed)= millimeter (Post processed)

Epoch 35GNSS

Epoch 25 – DUAL GPS

Epoch 10L1 only GPS

EPOCH

L1 GPS

GNSS

DUAL GPSSOKKIA

DUAL GPS

L1 only GPS

ASHTECH

GNSS DUAL GPS L1 only GPS

Magellan

LEICA system 1200 GNSS receivers

GX1210- L1GX1230-GNSS

L1 9600 L1 9200

L1 S60 L1 S66

SOUTH GPS

L1 S68 with Kinematic

DUAL S86S

DUAL S82

System OverviewSystem Overview

Space Segment

User SegmentMonitor Stations Diego Garcia Ascension Is. Kwajalein Hawaii

Colorado Springs

Control Segment

Colorado Springs

Designed for 24 Satellites Designed for 24 Satellites • Minimum 4 sats visible Minimum 4 sats visible

above 15deg cut-off above 15deg cut-off angle at any point of the angle at any point of the earth’s surface at any earth’s surface at any one time one time

• Orbits at 20,200 km Orbits at 20,200 km (12,600 mi) every 12 (12,600 mi) every 12 hourshours

• Equipped with Equipped with four(4)very accurate four(4)very accurate atomic clocks– 2 cesium atomic clocks– 2 cesium & 2 rubidium& 2 rubidium

• Life span- 7.5 to 12 yrsLife span- 7.5 to 12 yrs

Space Segment- satellites Space Segment- satellites orbiting the earthorbiting the earth

SatellitesSatellites

Broadcasts 2 carrier waves (L-band) constantly Broadcasts 2 carrier waves (L-band) constantly at the speed of light. at the speed of light.

L1 carrier – 2 codes (C/A & P) + Nav msg about L1 carrier – 2 codes (C/A & P) + Nav msg about sats orbit & clock corrections & sat healthsats orbit & clock corrections & sat health

L2 carrier – 1 code (P) L2 carrier – 1 code (P) Single frequency receiver– L1 onlySingle frequency receiver– L1 only Dual frequency receiver– L1&L2Dual frequency receiver– L1&L2 C/A – course acquisition for civilian useC/A – course acquisition for civilian use(1(1stst civil signal) civil signal) P – precise (military use)P – precise (military use)

Control SegmentControl Segment

The Ground Control Segment is comprised of six dedicated monitor stations and four ground antennas with uplink capabilities. Monitor stations track all satellites in view

Information from the monitor stations is processed at the Master Control Station (MCS) to determine satellite clock and orbit states and to update the navigation message of each satellite. This updated information is transmitted to the satellites via ground antennas

USER SEGMENT—anybody that receives and uses the GPS signal

GPS MODERNIZATIONGPS MODERNIZATION (2005) (2005)Goals:Goals: System-wide improvement in accuracy, availability, System-wide improvement in accuracy, availability,

integrity & reliabilityintegrity & reliability Robustness against interferenceRobustness against interference Improved indoor, mobile & urban useImproved indoor, mobile & urban use Interoperability with other GNSS constellationsInteroperability with other GNSS constellations Backward compatibility Backward compatibility

Block IIA IIR IIR-M,F Block III C/A, L1/L2 L2C, L5 L1C

Modernized GPS – Civil SignalsModernized GPS – Civil Signals

Second civil signal (L2C)Second civil signal (L2C) --designed to meet commercial needs for higher accuracy --designed to meet commercial needs for higher accuracy

through ionospheric correction, higher effective power & through ionospheric correction, higher effective power & improved data structure, reduced interference, speed up improved data structure, reduced interference, speed up signal acquisition, enable miniaturization of receivers, may signal acquisition, enable miniaturization of receivers, may enable indoor use (Began with GPS Block IIR-M in Sept. enable indoor use (Began with GPS Block IIR-M in Sept. 2005) 24sats in 20142005) 24sats in 2014

Third civil signal (L5)Third civil signal (L5) --designed to meet demanding requirements for --designed to meet demanding requirements for

transportation safety (safety-of-life); uses highly protected transportation safety (safety-of-life); uses highly protected Aeronautical Radio Navigation Service (ARNS) band; Begins Aeronautical Radio Navigation Service (ARNS) band; Begins with GPS Block IIF, first launch=2007 ; 24 sats= 2016with GPS Block IIF, first launch=2007 ; 24 sats= 2016

Fourth civil signal (L1C)Fourth civil signal (L1C) --designed with international partners to enable GNSS --designed with international partners to enable GNSS

interoperability ; Begins with GPS block III ; first interoperability ; Begins with GPS block III ; first launch=2013 ; 24 sats= 2021 launch=2013 ; 24 sats= 2021

How GPS Works– Position ComputationHow GPS Works– Position Computation

All All GPS positionsGPS positions are based on are based on measuring the measuring the distancedistance from the from the satellites to the GPS receiver. satellites to the GPS receiver.

The basic idea is that of The basic idea is that of resectionresection, if , if you know the distance to three you know the distance to three known points relative to your own known points relative to your own position, you can determine your position, you can determine your own position relative to those three own position relative to those three points.points.

Calculating DistanceCalculating Distance

By the formula By the formula D = VTD = VT VV= VELOCITY of radio = VELOCITY of radio

signal=299,792km/secsignal=299,792km/sec TT= TIME taken for the radio signal to = TIME taken for the radio signal to

travel from the satellite to receiver. travel from the satellite to receiver.

5 seconds4 seconds

Calculating TimeCalculating Time

you need to know when the signal left the satellite

This is a little harder to Calculate since ….

30

How Do We Know When the Signal Left the Satellite?

• The receiver and satellites use the same code

• They are synchronized to generate the code at the same exact time

• Then, the receiver looks at the incoming code from the satellite and determines how long ago the receiver generated that code

from satellite

from ground receiver

measure timedifference betweensame part of code

Methods Of Obtaining Methods Of Obtaining PositionPosition

Methods Of Obtaining PositionMethods Of Obtaining Position

11.. Autonomous, absolute Autonomous, absolute or simple navigationor simple navigation

--- This is the most simple --- This is the most simple technique employed by technique employed by GPS receivers to GPS receivers to instantaneously give a instantaneously give a position, height and position, height and accurate time. Used by accurate time. Used by hikers, ships that are far hikers, ships that are far out at sea & military. out at sea & military. Accuracy can only be Accuracy can only be better than 20m. better than 20m. This This method is subject to all method is subject to all error sources that error sources that degrades a GPS positiondegrades a GPS position. .

Sources Of Error That Degrade A GPS Sources Of Error That Degrade A GPS PositionPosition

Ionospheric & atmospheric delays– slows down satellite Ionospheric & atmospheric delays– slows down satellite signal while passing thru the ionosphere: solution=dual signal while passing thru the ionosphere: solution=dual frequency receiversfrequency receivers

Satellite & receiver clock errors—slight drift of satellite Satellite & receiver clock errors—slight drift of satellite clocks: solution= double differencing in post processingclocks: solution= double differencing in post processing

Multipath– occurs when GPS antenna is positioned close to a Multipath– occurs when GPS antenna is positioned close to a large reflecting surface such as building or lake. Signal does large reflecting surface such as building or lake. Signal does not travel directly to antenna but hits nearby object then not travel directly to antenna but hits nearby object then reflected into the antenna creating a false range: solution= reflected into the antenna creating a false range: solution= stay away from obstructions & use ground plane or choke stay away from obstructions & use ground plane or choke ring antenna and plan longer occupation times.ring antenna and plan longer occupation times.

Dilution of precision– measure of strength of satellite Dilution of precision– measure of strength of satellite geometry related to spacing & position of satellites in the geometry related to spacing & position of satellites in the sky: solution= observe as many satellites as possible, lower sky: solution= observe as many satellites as possible, lower values of DOP gives the most accurate position.values of DOP gives the most accurate position.

Selective availability– The control segment slightly alters the Selective availability– The control segment slightly alters the time of satellite clocks & broadcasts slightly different time of satellite clocks & broadcasts slightly different ephemeris: solution= use differential methodephemeris: solution= use differential method

Anti spoofing– encrypts the P-code into a signal called Y-Anti spoofing– encrypts the P-code into a signal called Y-code: solution= use decrypting device or differential methodcode: solution= use decrypting device or differential method

Methods Of Obtaining PositionMethods Of Obtaining Position

2. Differentially corrected position (DGPS).2. Differentially corrected position (DGPS). -- Errors affecting the measurement of satellite range -- Errors affecting the measurement of satellite range

can be completely eliminated or at least minimizedcan be completely eliminated or at least minimized --Principles –> a reference receiver is set up on a known --Principles –> a reference receiver is set up on a known

point and acts as base station. It calculates an point and acts as base station. It calculates an autonomous position and estimates very precisely the autonomous position and estimates very precisely the ranges to various satellites. It then works out the ranges to various satellites. It then works out the differencedifference betweenbetween thethe computed (from the input computed (from the input coordinates) and estimated range values. This coordinates) and estimated range values. This differences are known as differences are known as correctionscorrections. These corrections . These corrections were broadcast through a radio data link to the rover were broadcast through a radio data link to the rover receiver. The rover receiver also calculates ranges to receiver. The rover receiver also calculates ranges to satellites then applies the range corrections received satellites then applies the range corrections received from the base station. This lets it from the base station. This lets it calculate a much more calculate a much more accurate positionaccurate position. This method is used for inshore . This method is used for inshore hydrographic surveys, navigation & GIS data acquisition. hydrographic surveys, navigation & GIS data acquisition. Accuracy ranges from 1-2m 0r less.Accuracy ranges from 1-2m 0r less.

Methods Of Obtaining PositionMethods Of Obtaining Position

3. Differential Phase GPS3. Differential Phase GPS -- used mainly in control -- used mainly in control survey and related industries to achieve positioning survey and related industries to achieve positioning accuracies of 5-50mm. accuracies of 5-50mm.

--- it is a differential technique which means that a --- it is a differential technique which means that a minimum of two GPS receivers are always used minimum of two GPS receivers are always used simultaneously. simultaneously.

Post-Processing involves:Post-Processing involves: --- determining baseline vectors between pairs of --- determining baseline vectors between pairs of

receivers.receivers. --- computing the components of the baseline vectors --- computing the components of the baseline vectors

between observing stations (dX,dY,dZ). between observing stations (dX,dY,dZ). ---once the coordinates for one or more stations are ---once the coordinates for one or more stations are

known, new points can be determined with an accuracy known, new points can be determined with an accuracy relative to the relative to the known coordinatesknown coordinates..

GPS Coordinate SystemGPS Coordinate System

GPS uses WGS 84 ellipsoid GPS uses WGS 84 ellipsoid a= 6,378,137m; b=6,356,752.314ma= 6,378,137m; b=6,356,752.314m f= 1/298.25722f= 1/298.25722 Geocentric DatumGeocentric Datum Cartesian coordinate system is the Cartesian coordinate system is the

system used by GPS in defining the system used by GPS in defining the location of a point in space. It use location of a point in space. It use distances in the X,Y and Z axes from distances in the X,Y and Z axes from the origin (center of ellipsoid) the origin (center of ellipsoid)

The system of Cartesian coordinates is the most commonly used coordinate system. In two dimensions, this system consists of a pair of lines on a flat surface, or plane, that intersect at right angles. Each of the lines is called an axis and the point at which they intersect is called the origin. The axes are usually drawn horizontally and vertically and are usually referred to as the x and y axes, respectively. In Cartesian coordinates, a point on the plane whose coordinates are (2,3) is 2 units to the right of the y axis and 3 units up from the x axis. In three-dimensional Cartesian coordinates, the z axis is added so that there are three axes all perpendicular to each other.

© 1993-2003 Microsoft Corporation. All rights reserved.

Cartesian coordinates

Earth-Centered, Earth Earth-Centered, Earth Fixed System (ECEF)Fixed System (ECEF)

X axis = 0 lo

ngitude

X axis in plane o

f equator

Y axis = 90 E longitude

Y axis in plane of equator

center of mass of earth (0,0,0)Origin of datum

Z axis = Mean rotation axis (polar axis) fixed in time

Z

Cartesian & Geodetic CoordinatesCartesian & Geodetic Coordinates

P

Y

XY

X

Z

Cartesian Cartesian coordinates (X, Y, coordinates (X, Y, Z)Z)

Geodetic Geodetic coordinatescoordinates

(Lat, Long, Ht)(Lat, Long, Ht)

Local coordinate system-LUZON DATUM 1911All maps in Phil. were made using this datum

• Reference Ellipsoid is Clarke 1866 •a= 6,378,206.4m; b= 6,356,583.8m •f= 1/294.978

• Datum Origin at Balanacan marked on the ground

Latitude N 13° 33’ 41.00” Longitude E 121° 52’ 3.00” Geiod/Spheroid separation is zero Geodetic Surveys carried out by

• Astronomical observation• Triangulation and Traverse

The assumption GEOID/SPHEROID = zero

This assumption has generated a systematic error as the survey was extended away from the origin The two surfaces may intersect at the origin but these surfaces will never coincide because the ellipsoid is a regular surface while the geoid is not

OLD LUZON uses the MSL heights to compute Geographic Positions instead of Ellipsoidal hts.

The old luzon position is being computed at a point equal to the deflection of the vertical. These deflections are not equal in all

parts of the Geoid

OLD LUZON vs. PRS 92 GP OLD LUZON vs. PRS 92 GP computationscomputations

OLD LUZON uses the MSL heights to compute OLD LUZON uses the MSL heights to compute Geographic Positions instead of Ellipsoidal hts.Geographic Positions instead of Ellipsoidal hts.

PRS 92 uses the actual ellipsoidal height PRS 92 uses the actual ellipsoidal height transformed from GPS to compute the Geographic transformed from GPS to compute the Geographic Position of a pointPosition of a point

Triangulation of the PhilippinesTriangulation of the Philippines

USC&GS commenced fieldwork in January 1901 USC&GS commenced fieldwork in January 1901 until end of 1926. Triangulation survey was done until end of 1926. Triangulation survey was done simultaneously. Each party started survey by simultaneously. Each party started survey by astronomic observations – each on its own datumastronomic observations – each on its own datum

Insurrection was still in progress and this resulted Insurrection was still in progress and this resulted in bits of second and third order triangulation in bits of second and third order triangulation widely scattered throughout the islandswidely scattered throughout the islands

This accounts for the poor figures and This accounts for the poor figures and connectionsconnections

Triangulation of the PhilippinesTriangulation of the Philippines

So much datum had been established, to unify So much datum had been established, to unify Luzon , 13 datum’s were brought together into Luzon , 13 datum’s were brought together into Vigan Datum---this does not account for all the Vigan Datum---this does not account for all the other islands in Visayas and Mindanaoother islands in Visayas and Mindanao

To unite all datum’s, the Philippine datum was To unite all datum’s, the Philippine datum was established in 1911 to cover the whole country—established in 1911 to cover the whole country—which was later called Luzon datumwhich was later called Luzon datum

Principal Triangulation stations of The PhilippineIslands ---The starting points of all types of survey in the country (Topographic, Hydrographic and Cadastral)

These are 2nd order trig stations established from 1901 to 1926

NRMDP-- 1989NRMDP-- 1989 Natural Resources Management and Natural Resources Management and

Development ProjectDevelopment Project Australian assisted project of the DENR. Australian assisted project of the DENR. Geodetic survey component was Geodetic survey component was

undertaken by SAGRIC, Int’l (with Certeza undertaken by SAGRIC, Int’l (with Certeza as sub-contractor) in coordination with as sub-contractor) in coordination with NAMRIA through CGSDNAMRIA through CGSD

GEODETIC COMPONENTGEODETIC COMPONENT

Designed to provide support to other Designed to provide support to other components by establishing first order components by establishing first order control points. control points.

It also provided limited densification of It also provided limited densification of the network with second and third the network with second and third order stations. order stations.

It aims to determine the It aims to determine the transformation parameters relating transformation parameters relating WGS84 to LUZON Datum. WGS84 to LUZON Datum.

Analysis of the Triangulation and Analysis of the Triangulation and Birth of PRS 92Birth of PRS 92

Analysis of the old data set reveals large errors (includes punching Analysis of the old data set reveals large errors (includes punching and typographical) - up to 56m in lat and 80m in long. and typographical) - up to 56m in lat and 80m in long.

Old second order trig. Stations were recomputed and readjusted– Old second order trig. Stations were recomputed and readjusted– thus giving a modified G.P. and a new name– Philippine Reference thus giving a modified G.P. and a new name– Philippine Reference System 1992(PRS’92)System 1992(PRS’92)

PRS’92 PRS’92 datum quantitiesdatum quantities are the same as are the same as LUZON 1911 except for except for the Geoid-Ellipsoid separation (N=0.34m). the Geoid-Ellipsoid separation (N=0.34m).

PRS’92 is actually modified Luzon datum that has a more accurate PRS’92 is actually modified Luzon datum that has a more accurate and homogeneous set of coordinatesand homogeneous set of coordinates

A new network was established using GPS-- then called it the A new network was established using GPS-- then called it the Geodetic Network of the PhilippinesGeodetic Network of the Philippines

Error ellipses of triangulation stations

PRS’92PRS’92

A new network established using GPS under the Geodetic Survey Component of the Natural Resources Management and Development Project (NRMDP).

This new network has a more accurate and homogeneous set of coordinates, referred to the Clark 1866 spheroid and the modified Luzon Datum which is named Philippine Reference System 1992.

Seven parametersSeven parameters

PRS to WGS WGS to PRSPRS to WGS WGS to PRSTrans X = -127.622 +127.621531Trans X = -127.622 +127.621531Trans Y = -67.245 + 67.243395Trans Y = -67.245 + 67.243395Trans Z = -47.0433 + 47.047384 Trans Z = -47.0433 + 47.047384 Rot X = 3.068 - 3.06803751Rot X = 3.068 - 3.06803751Rot Y = -4.903 + 4.90297653Rot Y = -4.903 + 4.90297653Rot Z = -1.578 + 1.57807293Rot Z = -1.578 + 1.57807293Scale factor = -1.06002 + 1.06002112Scale factor = -1.06002 + 1.06002112

Heights & GEOIDSHeights & GEOIDS GPS heights are given in relation to the surface of GPS heights are given in relation to the surface of

the WGS84 Ellipsoid (Ellipsoidal Ht).the WGS84 Ellipsoid (Ellipsoidal Ht). Existing heights are Existing heights are orthometricorthometric heights heights

measured relative to measured relative to mean sea levelmean sea level. . Mean sea level corresponds to a surface known Mean sea level corresponds to a surface known

as as GEOIDGEOID. . The geoid can be defined as an equipotential The geoid can be defined as an equipotential

surface, i.e. the force of gravity is constant at any surface, i.e. the force of gravity is constant at any point on the geoid. point on the geoid.

The geoid is of The geoid is of irregular shape and does notirregular shape and does not correspond to any ellipsoid. correspond to any ellipsoid.

The density of the earth have an effect on the The density of the earth have an effect on the geoid-- causing it to rise in the more dense geoid-- causing it to rise in the more dense regions and fall in less dense regions.regions and fall in less dense regions.

Surveying with GPSSurveying with GPS

GPS measuring techniquesGPS measuring techniquesfor relative positioningfor relative positioning

Static – used for long lines, geodetic networks, Static – used for long lines, geodetic networks, tectonic plate studies etc. Offers high tectonic plate studies etc. Offers high accuracy over long distances but is accuracy over long distances but is comparatively slow. Minimum one(1) hour comparatively slow. Minimum one(1) hour observation for a 20km line with 5 satellites & observation for a 20km line with 5 satellites & GDOP of 8 or lower. Longer lines require GDOP of 8 or lower. Longer lines require longer observation times.longer observation times.

Fast Static or Rapid Static – used for Fast Static or Rapid Static – used for establishing local control networks, Network establishing local control networks, Network densification etc. Good for baselines up to densification etc. Good for baselines up to 20km and is much faster than Static 20km and is much faster than Static technique. Minimum eight(8)mins occupation technique. Minimum eight(8)mins occupation time using Dual freq. receivers & good time using Dual freq. receivers & good satellite constellation. satellite constellation.

Kinematic – used for topographic surveys, Kinematic – used for topographic surveys, (measuring many points in quick succession). (measuring many points in quick succession). Requires an initialization step to solve for Requires an initialization step to solve for the unknown integer ambiguity in the GPS the unknown integer ambiguity in the GPS signal. Needs reinitialization when passing on signal. Needs reinitialization when passing on obstructed areas. Minimum 15sec occupation obstructed areas. Minimum 15sec occupation time using Dual freq. receivers & good time using Dual freq. receivers & good satellite constellation. Longer lines require satellite constellation. Longer lines require longer observation time.longer observation time.RTK – uses a radio data link to transmit RTK – uses a radio data link to transmit satellite data from reference to rover. satellite data from reference to rover. Calculate & displays G.P. in real time. Subject Calculate & displays G.P. in real time. Subject to interference & line of sight blockage. to interference & line of sight blockage.

GPS measuring techniquesGPS measuring techniquesfor relative positioningfor relative positioning

GPS Precision and AccuracyGPS Precision and Accuracy

PrecisionPrecision GPS is a GPS is a very precisevery precise measurement method. measurement method. GPS gives consistent GPS gives consistent repeatability repeatability or precision– if or precision– if

the the same equipmentsame equipment and and careful measurement careful measurement techniquestechniques are used. are used.

AccuracyAccuracy GPS GPS accuracyaccuracy comes from: comes from: --Application of surveying methods such as --Application of surveying methods such as

network designnetwork design.. --Stability and accuracy of the --Stability and accuracy of the reference controlsreference controls.. ----RedundantRedundant measurements. measurements. --Application of --Application of precise set-up measurementsprecise set-up measurements..

Distances computed by GPS processing

GPS Field ProceduresGPS Field Procedures

GPS SURVEY WORKFLOW

PLANNING:Project Area, Reference Station Descriptions & Coordinates, Network Scheme with Proposed New Stations, Receivers & Accessories, Personnel, Field sheets, Description Forms

Mobilization & Courtesy Call

RECONNAISSANCE & MONUMENTATION

OBSERVATION & DOWNLOADING OF DATA TO COMPUTERSufficient Observation Time for the Project

IMPORT-CHECK & EDIT OBSERVATION INFOSuch As Antenna Heights, Where Measured, Station Names, Antenna Type, Receiver Serial No.

PROCESS GPS BASELINES

VIEW RAW DATA USING TIMELINE TO EDIT/REMOVE CYCLE SLIPS

PERFORM NETWORK ADJUSTMENTUsing WGS84 as Datum & Coordinate System

TRANSFORM TO PRS ‘92

DBASE

Planning a GPS surveyPlanning a GPS survey 1. The project purpose = Control survey or Topographic.

3. No. of GPS receivers to be used-- minimum= 2 Receivers Optimal = 4 receivers

2. Availability of Geodetic controls-- minimum =2 Ref. Stations

4. Appropriate number and length of observations –minimum = 2 sessions per station & minimum 1 hr per session (control)15 sec to 1 minute per point (kinematic)

5. Schedule of observations and station assignments—(date & time– use planning utilities)

6. No. of personnel and transport – Depending on number of Receivers

Network SketchNetwork Sketch

Make a sketch of the stationsMake a sketch of the stations- Old controls- Old controls- New points to be observed (approx. - New points to be observed (approx.

locations) locations)

Use sufficient existing controls in your networkUse sufficient existing controls in your network

- Three or four control stations - Three or four control stations distributed on the project area.distributed on the project area.

Network DesignNetwork Design

Design your network so that all stations have at Design your network so that all stations have at least three(3) independent baselines attached to least three(3) independent baselines attached to them. More baselines give more ways to compute them. More baselines give more ways to compute coordinates. coordinates.

Good network design– a GPS network design Good network design– a GPS network design consist of a set of consist of a set of baselinesbaselines between network between network points. The baselines connecting these points points. The baselines connecting these points should create should create closed figuresclosed figures with a minimum with a minimum number of sides such as number of sides such as trianglestriangles. Triangles will . Triangles will create a rigid network by adding more baselines, create a rigid network by adding more baselines, thus helping generate thus helping generate redundancyredundancy and multiple, and multiple, evenly distributed baselines to each point. evenly distributed baselines to each point.

NETWORK DESIGN

Each Station has at least three (3) Baselines attached Triangle figures were formed in each session/observation

The recommendation for connecting to existing controls are:

To AchieveTo Achieve First OrderFirst Order Second Second OrderOrder

Third OrderThird Order

MinimumMinimum 3 3 22 22

RecommenRecommendedded

4 or more4 or more 3 or more3 or more 22

Connection to Existing ControlsConnection to Existing Controls

Connections must be made to control of the same order or higher, because the coordinates of your new stations can only be as accurate as your reference stations.

ReconnaissanceReconnaissance

Ideally, all GPS stations should be free from Ideally, all GPS stations should be free from any obstructions above 15 degrees of the any obstructions above 15 degrees of the horizon, accessible and permanent. Away horizon, accessible and permanent. Away from radio station towers & transmission from radio station towers & transmission lines. But if there are no ideal sites, the lines. But if there are no ideal sites, the following can be accepted :following can be accepted :

Maximum obstruction of one(1) quadrant of Maximum obstruction of one(1) quadrant of the GPS station visibility plot with minimum the GPS station visibility plot with minimum distance of 10m.distance of 10m.

ReconnaissanceReconnaissance

Uniform maximum obstruction of Uniform maximum obstruction of 20 degrees above the horizon20 degrees above the horizon

Variable scattered horizon Variable scattered horizon obstruction of 25% of the GPS obstruction of 25% of the GPS station visibility plotstation visibility plot

MonumentsMonuments

Dimensions – 0.30m x 0.30m cement putty.Dimensions – 0.30m x 0.30m cement putty.

-- Concrete monument in the form of a -- Concrete monument in the form of a square base frustum with the following dimensions:square base frustum with the following dimensions:

STATIONSTATION TOP TOP BOTTOM BOTTOM DEPTHDEPTH HEIGHT HEIGHT First OrderFirst Order 0.30 m 0.40 m 0.30 m 0.40 m 1.00 m 1.00 m 0.20 m 0.20 m

Second Order 0.30 m 0.40 mSecond Order 0.30 m 0.40 m 1.00 m 1.00 m 0.20 m 0.20 m Third OrderThird Order 0.25 m 0.35 m 0.25 m 0.35 m 1.00 m 1.00 m 0.20 m 0.20 m Fourth Order 0.20 m 0.30 mFourth Order 0.20 m 0.30 m 0.80 m 0.80 m 0.20 m 0.20 m

Inscriptions – station name in capitals, year and Inscriptions – station name in capitals, year and agency name.agency name.

Station mark – any non- corrosive Station mark – any non- corrosive metal such as Copper nail or metal such as Copper nail or Brass rodBrass rod

Description – use standard NAMRIA Description – use standard NAMRIA form in describing a GPS station. form in describing a GPS station. Fill up all information including Fill up all information including sketches.sketches.

ObservationsObservations Field sheets – use Field sheets – use NAMRIA field sheets. Fill . Fill

up all information-- station name, antenna up all information-- station name, antenna ht., receiver serial no., measured to, ht., receiver serial no., measured to, antenna type, etc.antenna type, etc.

Antenna – indicate where measurements Antenna – indicate where measurements were taken.were taken.

-- Center antenna to station by -- Center antenna to station by plumb bob or optical plummet to the plumb bob or optical plummet to the nearest millimeter.nearest millimeter.

-- Measure heights before and after -- Measure heights before and after observation to nearest millimeter.observation to nearest millimeter.

Receiver settings – verify that settings for all Receiver settings – verify that settings for all receivers are compatible or the same, such receivers are compatible or the same, such as elevation mask, sync rates, SV enabled or as elevation mask, sync rates, SV enabled or disabled, data formats(no mixing of old & disabled, data formats(no mixing of old & new receivers)new receivers)

Data collection – avoid using electronic Data collection – avoid using electronic device within 10m, such as radio, cell phone, device within 10m, such as radio, cell phone, etc., while collecting data.etc., while collecting data.

-- for stations with obstructions, -- for stations with obstructions, longer observation times are advisable.longer observation times are advisable.

GPS OBSERVATIONGPS OBSERVATION Suggested minimum session lengths—Fast Static

6 satellites6 satellites 10 mins10 mins 20 mins20 mins

5 satellites5 satellites 15 mins15 mins 25 mins25 mins

4 satellites4 satellites 20 mins20 mins 35 mins35 mins

Up to 5 KmUp to 5 Km 5 Km to 10 5 Km to 10 KmKm

The times above are the minimum period of unbroken data, if in doubt record more data

If observations are being conducted in a remote area where the baselines cannot be processed and validated before the field teams leave the area consider longer observation times

PDOP should be less than 8 and preferably less than 5 particularly for shorter observation suchas Rapid Static. Try to avoid periods of high PDOP when planning observations.

Satellites should be above 20 degrees if possible.

GPS OBSERVATIONGPS OBSERVATION Suggested minimum session lengths-- Static

0-5Km0-5Km 5-10Km5-10Km

1 hour1 hour 2 hours2 hours

Single Frequency

Dual Frequency

10-20Km10-20Km 20-30Km20-30Km 30-50Km30-50Km 50-50-150Km150Km

Over 150 KmOver 150 Km

1 hour1 hour 2 hours2 hours 3 hours3 hours 4 hours4 hours 6 hours6 hours

GPS OBSERVATIONGPS OBSERVATION Suggested minimum session lengths– RTK, PPK

0-5Km0-5Km 5-10Km5-10Km

8 sec8 sec 15 sec15 sec

INITIALIZATION TECHNIQUES:

1. Known-Point Initialization

2. Static Initialization

3. Postprocessed On-The-Fly Initialization

4. Reoccupation Initialization

TIPS TO AVOID POOR PROCESSING RESULTS

Poor GPS processing results can occur for a variety of reasons, including:

•Field Blunders, such as:incorrect antenna height measurementincorrect naming of stationstripod centering error

•Inconsistencies in receiver setting such as:elevation maskssync rates (logging rate)SVs enabled or disabledData formats (if mixing older 4000 ST receivers with newer 4000 series receivers, such as 4000SSi, 4600LS, 4700 or 4800 receivers)

•Collecting data under marginal conditions, such as:observing too few satelliteshigh PDOPtoo many satellites at low elevation anglemany cycle slipsinsufficient observation time

STANDARDS OF ACCURACYSTANDARDS OF ACCURACY

1. First Order : 10 Parts per million (10 PPM)

(National Geodetic Network)

3. Third Order : 50 Parts per million (50 PPM)

2. Second Order : 20 Parts per million (20 PPM)

4. Fourth Order : 100 Parts per million (100 PPM)

1 cm/Km

2 cm/Km

5 cm/Km

10 cm/Km

1/100,000

1/50,000

1/10,000

1/20,000

Questions ?Questions ?