Bill Henning, PLS. · 2018-04-04 · • remote sensing and mobile mapping . 2...

1

Bill Henning, PLS.

• Static GNSS vs. RTK GNSS

• RTN vs. RTK

• RTX © vs. RTN

• PPP vs. differential processing

• OPUS-S vs. OPUS-RS vs. OPUS-P

• Passive vs. Active control

• Grid vs. Ground

• Precision vs. Accuracy

• RMS and other data collector/processing output

• Δ h vs. Δ H

• SPC vs. LDP

• Datum Issues and Legacy Control

• Remote Sensing and Mobile Mapping

2

-27

00

-25

00

-15

00

-10

00

-50

0

0

50

0

75

0

10

00

12

50

15

00

17

00

17

50

18

50

19

00

19

77

19

89

20

00

20

10

20

17

20

30

POSITIONING TECHNOLOGY-

A CARTOON GRAPH

TECHNOLOGY

YEAR

0.5' SAT IMAGERY, MOBILE TERR. LASER SCANNING, 0.10' AERIAL MAPPING, INTERNATIONAL NETWORKS, 24/7/365 SAT. COVERAGE

GNSS- GLONASS, GALILEO,

COMPASS/BEIDOU, INDOOR POSITIONING,

CM PPP

GPS

RTK

RTN

TOTAL STATION COMPASS THEODOLITE

STICKS AND STRINGS

GIS

RTX©

THE CHANGE FROM LABOR INTENSIVE TO TECHNOLOGY!

“Human knowledge is doubling every 10 years. The scientific knowledge produced between 1987 and 1997 is greater than that produced in all mankind’s history”.

Michio Kaku- renowned theoretical physicist

WHAT WILL GNSS BE LIKE IN TEN YEARS?

3

“GNSS”

GLONASS

GPS

GALILEO

COMPASS (BEIDOU-2)

http://www.navipedia.net/index.php/GLONASS_Space_Segment

Orbital planes of the Compass-Beidou (CNSS) constellation: • The 27 MEO satellites will be deployed into 3 orbital planes with an inclination of 55.5º. The nominal orbital altitude is 21,500 -24100 km. • Five GEO satellites at the equatorial longitudes of: 58.75ºE, 80ºE, 110.5ºE, 140ºE and 160ºE (regional system). • Three IGSO (Inclined Geosynchronous Orbit) satellites.

4

GNSS CONSTELLATIONS

DUAL CONSTELLATION RT POSSIBILITIES: GPS ≥ 5, GLN = 0 GPS = 4, GLN = 2 GPS = 3, GLN = 3 GPS = 2, GLN = 4 (Can't initialize with only GLN Sats.)

GPS AND GLN

BEST SCENARIO = 7 OR MORE GPS

GLN “K” SATS WILL HAVE A CDMA (L3) FORMAT SIGNAL

5

GPS LAUNCH HISTORY

GPS SATELLITES MAINTAIN TIME TO 1 SECOND PRECISION IN A MILLION YEARS! NEW SVNS KEEP PRECISION TO 8 NANOSECONDS – POSSIBLY EVEN BETTER IF HYDROGEN MASER CLOCKS ARE IMPLEMENTED.

GLONASS STATUS

6

GALILEO- OFF THE GROUND OCTOBER 21, 2011

2 IOV SATELLITES, EUROPEAN SPACEPORT, FRENCH GUIANA, RUSSIAN SOYEZ ROCKET (SPUTNIK, YURI GREGARIN)

AT LEAST 22 SATELLITES UNDER CONTRACT (27 PLUS 3 SPARES PLANNED)

EVERY EPOCH OF OBSERVATION MUST COMPUTE CHANGE IN POSITION DUE TO EARTH ROTATION, SATELLITE ORBIT CHANGE AND RELATIVITY!

AT “C”, 1 NANOSECOND = 30 CM!

CORRECTIONS TO SVN’S clocks before launch: S.R.= +7 μ sec., G.R = -45.9 μ sec. = -38 μ sec./ day!

THE NATIVE CONDITION OF THE GNSS SIGNAL

7

THE INTEGER AMBIGUITY

Dl = First Partial Wavelength

Nl = Integer Ambiguity

Resolving the integer ambiguity allows phase

measurements to be related to distances

Distance = Nl + Dl

WGS 84

X,Y,Z

RESOLUTION TO ROUGHLY 2 mm

λ1 = 19.03 cm λ2 = 24.42 cm λ5 = 25.48 cm

The ambiguity is an integer number (a multiple of the carrier wavelength).

The integer is different for the L1 and L2 phase observations.

The integer ambiguity is different for each satellite-receiver pair.

The integer ambiguity is a constant for a particular satellite-receiver pair for all

epochs of continuous tracking (that is, as long as no cycle slips occur)

The carrier phase measurement from one observation epoch to another is a

measure of the change in satellite-receiver range.

The determination of the cycle ambiguity integer is known as ambiguity

resolution, and is generally not an easy task because of the presence of

other biases and errors in the carrier phase measurement.

THE AMBIGUITY SEARCH….

8

IONO & TROPO LAYERS AND THEIR EFFECT ON THE GNSS SIGNAL

SUNSPOT CYCLE – EFFECTS IN THE IONOSPHERE

• Sunspots follow a regular 11 year cycle

• We are just past the low point of the current cycle

• Sunspots increase the radiation hitting the earth's upper atmosphere and produce an active and unstable ionosphere

2013

http://www.swpc.noaa.gov/

9

troposphere

TROPOSPHERE DELAY The more air molecules, the slower the signal (dry delay)

High pressure, Low temperature

90% of total delay

relatively constant and EASY TO CORRECT FOR

The more water vapor in the atmosphere the slower the signal (wet delay)

High humidity

10% of total delay

Highly variable and HARD TO CORRECT FOR

ORBITAL ERRORS CONTRIBUTING TO PPM ERRORS

(See user guidelines references for Graphic: Ahn, 2005)

2-5 m USED IN RTK (SOME RTN CAN USE

ULTRA-RAPID ORBITS)

1 cm! POST PROCESSED

AFFECTS VERTICAL MORE TRHAN HORIZONTAL

10

• CYCLES PER METER FOR RANGE • RECEIVER CLOCK ERROR/BIAS • SATELLITE CLOCK ERROR • INITIAL/CARRIED CYCLE ESTIMATE • IONOSPHERIC ADVANCE/ GROUP DELAY • TROPOSPHERIC SIGNAL REFRACTION/DELAY • RECEIVER HARDWARE DELAYS • SATELLITE HARDWARE DELAYS • RECEIVER WHITE NOISE • MULTIPATH

THE CYCLE COUNT COOKBOOK- USING DIFFERENCING TO ELIMINATE OR

REDUCE COMMON ERRORS IN THE RECEIVER AND SATELLITE

• RECEIVER HARDWARE DELAYS •SATELLITE HARDWARE DELAYS • RECEIVER CLOCK BIAS • SATELLITE CLOCK BIAS

ELIMINATED WITH DIFFERENCING

• IONO DELAY •TROPO DELAY SAME AS BASE WITH SINGLE BASE

INTERPOLATED WITH RTN

• MEASUREMENT NOISE (HIGHER GRADE RECEIVERS = LESS NOISE) • MULTIPATH

NOT ELIMINATED WITH DIFFERENCING

11

OR MODELED BY RTN

SINGLE DIFFERENCE

Two receivers, one satellite,

same epoch.

Eliminates satellite clock error,

satellite hardware error

OR

Two satellites, one receiver

same epoch,

eliminates receiver clock error,

receiver hardware error

12

SINGLE DIFFERENCE DOUBLE DIFFERENCE

Double differencing: two receivers, two satellites, same epoch (two Single

Differences). Eliminates receiver clock error, receiver hardware error, reduces other

errors.

13

DOUBLE DIFFERENCE

= difference between two single differences of two receivers and

TWO satellites at the same epoch

TRIPLE DIFFERENCING

Triple difference – difference of two double differences at two epochs for two

satellites and two receivers. Detects cycle slips

14

TRIPLE DIFFERENCE

Cancels Double Difference integer cycles

SOME INTEGER FIXING TECHNIQUES (FOR RTK, DUAL FREQUENCY ALSO ENABLES OTF

INITIALIZATION) • Wide Laning (L1 – L2) = c (speed of light) ÷

(1575.42 MHz – 1227.60 MHz) or 299,792.458 Km/sec ÷ 347.82 MHz = 0.862 m wave length.

• Narrow Laning (L1 + L2) = c (speed of light) ÷ (1575.42 MHz +

1227.60 MHz) or 299,792.458 Km/sec ÷ 2803.02 MHz = 0.107 m wave length

• Iono Free f(L1)ion-free = a1.f(L1) + a2.f(L2)

with a1 = f12/(f1

2 - f22 ) and a2 = - f1 . f2 /(f1

2 - f22 )

• Triple Differencing

• Kalman Filtering

• Double Differencing

15

INTEGER SEARCH TO GET TO THE BOTTOM LINE……..

SURVEYORS

GEODESISTS

16

DATUM/ADJUSTMENT/EPOCH DIFFERENCES BETWEEN RTN, LEGACY CONTROL, PASSIVE MARKS AND THE NSRS CAN CREATESITE CONTROL PROBLEMS.

• 2 HUBS AND A PK

• LOCAL CONTROL

• SPC MONUMENTS

• CORS- REMOTE POSITIONING

• RTN GNSS

• IGS GNSS

• UBIQUITOUS RTX ©, PPP, STAND ALONE POSITIONING

17

≥200 RTN WORLDWIDE ≥80 RTN USA ≥37 DOT

ACADEMIC/SCIENTIFIC

SPATIAL REFERENCE CENTERS

VARIOUS DOTS + MACHINE GUIDANCE

COUNTY

CITY

GEODETICSURVEYS(NC,SC)

MANUFACTURERS

VENDOR NETWORKS

AGRICULTURE

MA & PA NETWORKS

MAJOR RTN IN THE USA (JAN 2013)

18

STAND ALONE POSITIONING IN CENTIMETERS: RTX ©

GPS IS MAINTAINED BY THE DoD IN WGS 84 GLONASS IS MAINTAINED IN PZ 90.02 GALILEO IS MAINTAINED IN ITRS OUR NATIONAL GEOMETRIC DATUM IS NAD 83 – BASED ON CORS ANTENNAS IN THE AIR OUR NATIONAL VERTICAL DATUM (ORTHOMETRIC HEIGHTS) IS NAVD 88 - BASED ON NAVD 88 BENCH MARKS IN THE GROUND WE WORK IN MAP PROJECTIONS: UTM, SPC, LDP

KNOWING DATUMS AND PROJECTIONS CAN HELP WITH ANALYZING ERRORS

19

DATUM DEFINITIONS IN THE USA

• NAD 83- USA

• ITRS- “OLD”CORS/WORLD

• WGS 84- GPS (DoD)

• IGS 08 – “NEW” CORS

• NRS 22 (?) – NEW GEOCENTRIC

• NGVD 29

• NAVD 88

• NAVD 22 (?)

HORIZONTAL/ GEOMETRIC: VERTICAL/GEOPOTENTIAL:

PROJECTIONS FROM DATUMS:

• SPC

• UTM

• LDP

NAD 83

ITRF 2000

SILVER SPRING, MD

20

NAD 83 VELOCITIES (GOLD)

ITRF 2000 VELOCITIES (BLUE)

SANTA CRUZ, CA

21

• MOVE GEOCENTER TO SOME EPOCH OF IGS

• FIXED ON NORTH AMERICAN PLATE?

• ASSIGN VELOCITIES TO THE STATIONS

• ACCESSED THROUGH THE CORS NETWORK

NAVD 88 suffers from use of bench marks that: Are almost never re-checked for movement •Disappear by the thousands every year •Are not funded for replacement •Are not necessarily in convenient places •Don’t exist in most of Alaska •Weren’t adopted in Canada •Were determined by leveling from a single point, allowing cross-country error build up (Has been proven to be ~ 1 meter tilted across CONUS (again, based on the independently computed geoid from the GRACE satellites)

NEW NATIONAL VERTICAL DATUM:2022(?) WHY ISN’T NAVD 88 GOOD ENOUGH ANYMORE?

RE-LEVELING WOULD COST 200 MILLION TO 2 BILLION $$

22

• BASED ON PURE GRAVIMETRIC GEOID, ACCURATE TO 1 CM VIA GRAV-D PROJECT

• VERTICAL DATUM BROUGHT TO SITE AT 2 CM ACCURACY

• ACCESSABILITY: BROUGHT TO A PROJECT SITE VIA ACTIVE REFERENCE STATIONS (NATIONAL CORS), DENSIFIED TO PROJECT ACCURACY NEEDS AT SITE. (ALTERNATIVE: LOCALIZE TO BMs PREVIOUSLY TIED TO THE DATUM-CAVEAT EMPTOR)

• SECONDARY ACCESS (USE AT YOUR OWN RISK)

– PASSIVE MARKS THAT HAVE BEEN TIED TO THE NEW VERTICAL DATUM

– NGS WILL PROVIDE A “DATA SHARING” SERVICE FOR THESE POINTS, BUT THEIR ACCURACY (DUE TO EITHER THE QUALITY OF THE SURVEY OR THE AGE OF THE DATA) WILL NOT BE A RESPONSIBILITY OF NGS

WHAT ABOUT THE PASSIVE MARKS?

23

• NAVD 88 CONVERSION TO NEW DATUM

– A CONVERSION WILL BE PROVIDED BETWEEN NAVD 88 AND THE NEW DATUM

• ONLY WHERE RECENT GNSS ELLIPSOID HEIGHTS EXIST TO PROVIDE MODERN HEIGHTS IN THE NEW DATUM

WHAT ABOUT CONVERTING TO/FROM NAVD 88?

IN MARYLAND NAVD 88 TO “NVD 22” ~ 1.1’

46

AL, AK, CA, CT, FL, GA, LA, MD,

MS, NJ, NY, NC, OR, RI, SC, WA

Privately Owned

Uplands

State Owned

Tidelands

Territorial Seas

State Submerged Lands

Contiguous Zone

Exclusive Economic Zone

Federal Submerged Lands

High Seas

Privately

Owned

State

Owned

TX

3 n. mi.

12 n. mi.

200 n. mi.

Privately

Owned

State

Owned

DE, MA, ME, NH, PA, VA

MHHW

MHW

MLLW Chart Datum

Importance of Vertical Datums and Water Levels to Shoreline Property

24

ACCOMPLISHING ACCURATE DATA COLLECTION 95% CONFIDENCE

• SBAS- 3 M H, 6 M V

• COMMERCIAL DGPS – FEW DM, $$

• USCG BEACON – METER+

• CLASSICAL SURVEYING – 2-4 CM, LABOR/TIME INTENSIVE, $$$

• USER BASE RTK – 2-4 CM H, 3-5 CM V

• RTN – 2-4 CM H, 4-7 CM V

• RTX ©, PPP - CENTIMETERS POSSIBLE

• AERIAL MAPPING - .15 M H, .25 M V, $$$

• SATELLITE IMAGERY – 0.5 METER H RESOLUTION, 3 M LOCATION, $$$

• LOW ALTITUDE AERIAL IMAGERY – 2-4 CM H, 3-5 CM V, $$

• TERRESTRIAL LASER SCANNING – PROJECT SITES ONLY, 0.015 H, 0.02 V, $$

• MOBILE MAPPING SYSTEMS (MMS) – 0.025 H, 0.04 V, $$$

25

Height

Modernization

-faster

-cheaper

-Nearly as good

differential leveling

GNSS

HEIGHT MODERNIZATION- BACKGROUND

CHA – CHING $$$$$$$ ♪♪♪

EXPECTED HEIGHT MOD ACCURACIES

• GPS-Derived Ellipsoid Heights

– 1.5 centimeters (following NOS NGS-58 Guidelines)

• Geoid Heights (GEOID12A)

– Relative differences typically less than 1 cm in 10 km

– 1.6 cm RMS about the mean nationally

– 0.5 cm error in 10 Km

• Leveling-Derived Heights

– Less than 1 cm in 10 km for third-order leveling = FIXED

NOAA Technical Memorandum NOS NGS-58

GUIDELINES FOR ESTABLISHING GPS-DERIVED ELLIPSOID HEIGHTS (STANDARDS: 2 CM AND 5 CM) VERSION 4.3 David B. Zilkoski Joseph D. D'Onofrio Stephen J. Frakes Silver Spring, MD November 1997

U.S. DEPARTMENT OF National Oceanic and National Ocean National Geodetic COMMERCE Atmospheric Administration Service Survey

26

RECAP OF HEIGHTS WE USE:

•LMSL – From local tide guages •ORTHOMETRIC – From leveling, GNSS derived •DYNAMIC – From leveling or computed from ortho •ELLIPSOID – From GNSS (WGS 84, NAD 83, ITRS datums)

•GEOID – A gravimetric or hybrid model •ASSUMED “ELEVATIONS” – Leveled differences with no gravity

27

• GNSS ECEF X,Y,Z (WGS 84 & PZ90.02)

NAD 83 (,l,h) SPC N,E,h

+ GEOID XX = SPC N,E,H

OR

CALIBRATE TO 4-5 SITE POINTS IN THE DESIRED DATUM. THIS IS USED TO LOCK TO PASSIVE

MONUMENTATION IN THE PROJECT AREA AND CREATES A BEST FIT PLANE. ADD A GEOID MODEL

FOR ALL BUT SMALL PROJETS

GNSS TO A LOCAL DATUM TO A PROJECTION

TYPES OF PROJECTIONS TYPICALLY USED IN OUR WORK

• State Plane projections (SPC) Lambert conformal secant Transverse mercator Oblique mercator

• Universal Transverse Mercator (worldwide) • Tangent plane – one point in project center • Transverse Mercator – typical GNSS manufacturers’

calibration • Low Distortion – user defined at project ellipsoid

height

All projections introduce distortion in one or all of: shapes, distances, azimuths, or areas. CONFORMAL PROJECTIONS MAINTAIN SHAPES AND ANGLES. THEREFORE, THEY DO NOT MAINTAIN DISTANCES OR AREAS.

28

Normal to ellipsoid

THREE SURFACES COLORADO DOT AND MODIFIED STATE PLANE

29

SPC GRID

NORTH

FOUR SURFACES

COMBINED FACTOR

MODIFIED SPC- DOES NOT REDUCE CONVERGENCE ANGLE OR MINIMIZE DISTORTION

30

LDP ELLIPSOID HEIGHT FACTOR Ron Singh ODOT/OGUG Low Distortion Projections Workshop 4 November, 2008

31

DEFINING LDP

1.Define the project area and choose a representative ellipsoid height (ho). 2.Place the projection axis (central meridian for TM, standard parallel for LCC) near the center of the project. 3.Compute the scale at the project axis using ho. Use the formula: ko = 1 + (ho / RE) , where ko = scale at projection axis, RE = radius of earth (ellipsoid) at the project latitude (a geometric mean radius of curvature of 6,372,000 m or 20,906,000 ft works reasonably well for the coterminous US). Round ko to five or six decimal places (use at most seven for small areas). 4.Define false northing and easting for an origin so that all project coordinates are positive. Make the coordinates at the central meridian and a parallel of origin (south of project) using the smallest integer values that give positive coordinates everywhere in the area of interest. Also define the latitude and longitude of grid origin (including central meridian and standard parallel, as applicable) to no more than the nearest arc-minute. The purpose of this step (and rounding ko to six decimal places) is to provide a clean coordinate system definition. 5. Check passive control (or points of known topographic height) at the project extremes for distortion (both in extremes of area and height). If the computed distortion based on these ellipsoid height check points is too high, the projection axis scale factor can be adjusted to reduce distortion.

MORE LDP INFORMATION

MICHAEL DENNIS: [email protected] OR http://www.ngs.noaa.gov/PUBS_LIB/NGSRealTimeUserGuidelines.v2.1.pdf (APPENDIX E IN NGS REAL TIME GNSS SINGLE BASE GUIDELINES) SHAWN BILLINGS, PLS.: AMERICAN SURVEYOR MAGAZINE ARTICLES, AUGUST 2013 (VOL. 10 NO. 9), SEPTEMBER 2013 (VOL. 10 NO. 10)

mailto:[email protected]

http://www.ngs.noaa.gov/PUBS_LIB/NGSRealTimeUserGuidelines.v2.1.pdf


32

• LARGE PROJECTS OR CORRIDOR SURVEYS SHOULD START WITH STATIC GNSS

• LARGE PROJECTS CAN USE THE NGS GPS DERIVED HEIGHT GUIDELINES FOR HORIZONTAL AS WELL AS VERTICAL CONTROL

• IN NEW JERSEY, SMALL PROJECTS CAN USE RT POSITIONING AND ELIPSOID HEIGHT DIFFERENCES FOR ORTHOMETRIC HEIGHTS.

• BEWARE OPUS DERIED VERSUS LEGACY PASSIVE CONTROL DIFFERENCES.

• KNOW WHAT DATUM/ADJUSTMENT/EPOCH ARE TO BE USED FOR YOUR PROJECT

• LOCALIZATION IS GOOD FOR ANALYZING THE AVAILABLE CONTROL

PROJECT PLANNING THOUGHTS

33

PLAN YOUR GNSS CAMPAIGNS TO AVOID

DOWN TIME

• SPACE WEATHER • DOP • SATS • GNSS OR GPS?

WHAT GNSS METHOD SHOULD I USE FOR MY PROJECT?

STATIC? • BEST POSITIONING

• INTEGRATED ADJUSTMENT FOR MULTPLE STATONS

• EASY CONTROL DATA CAPTURE

• CAN PROVIDE 2 CM ORTHO HEIGHTS

• TAKES LONGER

• NEED TO PROCESS DATA IF DONE IN HOUSE

• OPUS-S & OPUS-RS GIVE POINT POSITIONS, NOT INTEGRATED ADJUSTMENT

REAL TIME? • FASTEST

• ADEQUATE POSITIONING

• USER MUST BE AWARE OF FIELD PROCEDURES

• USE RT IF THE SITE IS TO BE CALIBRATED

• RTN CAN GIVE NATIVELY INADEQUATE ORTHOMERIC HEIGHTS (BUT USUALLY HORIZONTAL POSITIONS ARE GOOD)

• LESS METADATA

34

GNSS POSITIONING CHOICES- SUMMARY

STATIC – BEST POSSIBLE GNSS POSITION. Sub-centimeter horizontal and 1-2 centimeters vertical precisions. “Network session” style. Campaign static requires planning for conditions and logistics. 30+ minute set ups. L1 possible, but dual+ frequency recommended. Requires your post processing or NGS OPUS processing with certain requirements. Rapid or final orbits available. OPUS-PROJECTS will enable network solutions, while OPUS-S, OPUS-RS & OPUS-DB are point positions only. NEAR REAL-TIME – FASTEST METHOD FOR SURVEY GRADE POSITIONS. Typically 1 centimeter horizontal and 2 centimeters vertical relative to the base OR “coupla” centimeters horizontal & “many” centimeters vertical to RTN. Few seconds to 3 minutes point positions. Dependent on many variables, e.G. - Accuracy of base/RTN, distance to base/RTN, relative weather, multipath, robust communication, broadcast orbit data, shot comparisons, knowledge & techniques of the user. Processing done in the rover in the field. AUTONOMOUS - FASTEST METHOD FOR A BALLPARK POSITION. 3-5 meters. No phase differential processing is performed- uses code or smoothed code point positions. Few seconds per position. Good for raw navigation for point recovery. Note: future GNSS constellations & signals may yield near decimeter accuracy.

RTN ALIGNED TO CORS AT 1 CM IN EACH COMPONENT (X,Y,Z) & 2 CM ORTHOMETRIC

2022 NEW PROJECT CONTROL – ACCESS TO NSRS

NATIONAL CORS = GEOMETRIC &

GEOPOTENTIAL TRUTH

EXISTING PASSIVE MARKS- HORIZONTAL WITH OR WITHOUT VERTICAL

EXISTING PASSIVE BENCH

MARKS

NEW PROJECT CONTROL

35

GNSS METHOD 95% PRECISION: HORIZONTAL 95% PRECISION: VERTICAL TIME ON POINT NOTES

STATIC: CORS 2 CM 3 CM HOURS

1.5 CM 2 CM 4 HOURS

STATIC: OPUS-S 2 CM 3 CM HOURS

1.5 CM 2 CM 4 HOURS

STATIC: OPUS-RS 2 CM 5 CM MINUTES SEE OPUS RS MAP

OPUS-RS AVG. OF 2 OR MORE 1.5 CM 2.5 CM

STATIC: MULTI RECEIVER ≤ 1 CM ≤ 1.5 CM 30 MINUTES USING HTMOD GUIDELINES

CONNECTED SESSIONS

RTK 1.5 CM 2.5 CM 1 SECOND-5 MINUTES TO LOCAL BASE

USING NGS GUIDELINES

RTN 2 CM 3-5 CM

GEODETIC LEVELING N/A 3 MM N/A 3RD ORDER

EXPECTED PRECISIONS FROM VARIOUS GNSS POSITIONING

METHODS

PRECISE ORTHOMETRIC HEIGHTS FROM GNSS ARE MUCH HARDER TO ACHIEVE THAN

HORIZONTAL POSITIONS

SOME REASONS:

• ±120˚ COVERAGE RATHER THAN ±300˚

• ATMOSPHERIC EFFECTS ON THE GNSS SIGNAL CAUSE GREATER UNCERTAINTY IN THE VERTICAL

• ANTENNA PHASE CENTER VARIATION AFFECTS THE VERTICAL MORE

• BROADCAST/ ULTRA-RAPID ORBITS

• ERRORS IN EACH COMPONENT

OF THE: H = h – N ACCUMULATE

36

USING NAD 83 ELLIPSOID HEIGHTS WITH THE HYBRID GEOID FOR ORTHO HEIGHTS

NAD 83 (HARN) USE GEOID O3 NAD 83 (CORS 96) USE GEOID

09 NAD 83 (2007) USE GEOID 09 ITRF USE SCIENTIFIC GEOID

(USGG) NAD 83 (2011) USE GEOID 12

H88 = h83 – N12a

CONVERSION SURFACE: GRAVIMETRIC GEOID TO HYBRID GEOID

• EGM08 + NGSDEM99 +KMS98 (Andersen and Knudsen 1998) offshore Free-air gravity anomaly (FAGA) field with the GSFC00.1 model (Wang 2001)

• ITRF96/NAD83 TRANSFORMATION

• NAVD 88 BIAS (-52 CM)

• TILT (0.15 PPM, 327 AZIMUTH)

• LOCAL GPS/LEVELING/GEOID MISFIT THEREFORE: USGG2012 - CONVERSION SURFACE = GEOID12a

72

37

4 HYBRID GEOID MODELS ACROSS BALTIMORE COUNTY, MD

38

COMMENTS ON GPS LOCALIZATION

• A GPS LOCALIZATION CAN PERFORM THE FOLLOWING:

– TRANSLATION

– ROTATION

– SCALE IF DESIRED (OR NOT)

• A GPS LOCALIZATION DOES A BEST FIT OF THE GPS OBSERVATIONS TO THE NORTHINGS, EASTINGS AND/OR ELEVATIONS.

• A GPS LOCALIZATION CAN ALSO DO:

– A SINGLE POINT HEIGHT ADJUSTMENT

– AN INCLINED PLANE ONLY TO MULTIPLE POINTS

– AN INCLINED PLANE WITH A GEOID MODEL TO MULTIPLE POINTS

COMMENTS ON GPS LOCALIZATION

• A LOCALIZATION IN A PROJECT WITH A DEFINED PROJECTION CREATES AND HORIZONTAL AND VERTICAL ADJUSTMENT TO THAT PROJECTION.

• A LOCALIZATION IN A PROJECT USING STATE PLANE COORDINATES CREATES AN ADJUSTMENT WITH LARGE GRID/GROUND DIFFERENCES THAT CAN BE A PROBLEM

• A LOCALIZATION IN A PROJECT USING “NO PROJECTION / NO DATUM USUALLY CREATES A TRANSVERSE MERCATOR PROJECTION AT THE FIRST POINT OF THE PROJECT.

39

LOCALIZING TO PROJECT CONTROL WITH GNSS

• ≥ 4 H & V, KNOWN & TRUSTED POINTS FORMING A RECTANGLE

• EVALUATE LOCALIZATION RESIDUALS-OUTLIERS

• DO ANY PASSIVE MARKS NEED TO BE HELD?

•ARE LEGACY PLANS BASED ON PASSIVE CONTROL ON SITE?

• RT BASE WITHIN A CALIBRATION SHOULD OBTAIN AQUALITY

TIE TO NEAREST CALIBRATION POINT

• SAME OFFICE & FIELD CALIBRATION USED

• 2 POINT VERTICAL CALIBRATION IS POSSIBLE-IF YOU TRUST

THE ELEVATIONS

POSITIONING PRECISION VS.

POSITIONING ACCURACY

PRECISION IS THE STATISTICAL REPEATABILITY OF MEASUREMENTS. AS AN EXAMPLE, THIS CAN BE A REMEASURED SURVEY LINE OR A REDUNDANT GNSS OCCUPATION. E.G. “RMS” OR “RESIDUALS”

ACCURACY IS THE ALIGNMENT OF THE POSITION OR MEASUREMENT TO THE “TRUTH”. TRUTH CAN BE A DATUM REPRESENTED BY THE CORS SYSTEM, LEGACY PASSIVE MONUMENTS , OR A RAILROAD SPIKE DRIVEN INTO A TREE.

40

PRECISION vs. ACCURACY

PRECISE – NOT ACCURATE

ACCURATE AND PRECISE

ACCURATE – NOT PRECISE

NOTE: SPREAD OF SOLUTION REFLECTED IN THE “RMS”. HIGH RMS DOES NOT NECESSARILY MEAN A BAD RESULT

KEY

“TRUTH”

LARGE PROJECTS USING STATIC GNSS

NOAA Technical Memorandum NOS NGS-58

GUIDELINES FOR ESTABLISHING GPS-DERIVED ELLIPSOID HEIGHTS(STANDARDS: 2 CM AND 5 CM)VERSION 4.3

David B. ZilkoskiJoseph D. D'OnofrioStephen J. Frakes

Silver Spring, MD

November 1997

U.S. DEPARTMENT OF National Oceanic and National Ocean National GeodeticCOMMERCE Atmospheric Administration Service Survey

2 CM &

5 CM STANDARDS

41

Network / Local Accuracy

NSRS

HARN/Control Stations (75 km)

Primary Base (40 km)

Secondary Base (15 km)

Local Network Stations (7 to 10 km)

GPS ELLIPSOID HEIGHT HIERARCHY

CORS

42

EXAMPLE: FAIRFAX COUNTY, VA:

HTMOD PROJECT & NEW NAVD 88 ORTHOMETRIC HEIGHTS:

PLANNING

OBSERVATION PROCESSING ADJSTMENT

A LOOK AT STATIC GNSS POSITIONING

43

SATELLITES/ DOP WITH OBSTRUCTIONS SATELLITES/ DOP WITH OBSTRUCTIONS

44

WWW.SWPC.NOAA.GOV SWPC WARNING

45

OBSERVATION PLANNING:

HTMOD SESSIONS TO

CONNECT CLOSEST

NEIGHBORS

Bench Mark G 506

ESTABLISH A STABLE ECCENTRIC POINT AND TRANSFER THE ORTHOMETRIC HEIGHT USING PROPER LEVELING TECHNIQUES

46

FIELD REQUIREMENTS SUMMARY- FOR HTMOD & ALL STATIC GNSS

• DUAL FREQUENCY RECEIVERS

• GEODETIC ANTENNAS

• FIXED HEIGHT TRIPODS, VERIFY HEIGHT

• 5 HOUR PRIMARY CONTROL OCCUPATIONS WITH MET DATA

• REDUNDANT 30 MINUTE NETWORK CONTROL OCCUPATIONS

• OCCUPY CLOSEST NEIGHBORS

• OCCUPY BENCH MARKS ≤ 20 KM SPACING

• SET ECCENTRICS AS NEEDED

• BASELINES ≤ 10 KM, AVG. 7 KM

• PDOP ≤ 4.0

• PICTURES AND TIES TO MONUMENTS

• COMPLETE LOG FOR EACH OCCUPATION

47

ADJUSTMENT OF PRIMARY NETWORK STATIONS

FROM CONTROL

Horizontal Adjustment (Latitude, Longitude, Ellipsoid Heights)

• Minimum Constrained [One fixed station] – Fix latitude, longitude and ellipsoid height at one station

– Resolve all blunders and large residuals – Determine which Control and known Primary Base

Station coordinates should be fixed

• Constrained [All suitable stations fixed] – Fix latitude, longitude, and ellipsoid heights at Control

and known Primary Base Stations

– Make sure the constraints did not distort the project

NOTE - Geoid model NOT applied at this time

FAIRFAX COUNTY

CONTROL & PRIMARY STATIONS

48

ADJUSTMENT OF LOCAL NETWORK STATIONS

Horizontal Adjustment (Latitude, Longitude, Ellipsoid Heights)

• Minimum Constrained [One fixed station] – Fix latitude, longitude and ellipsoid height at one station

– Resolve all blunders and large residuals – Evaluate coordinates at Control and Primary Base

Station • should not be greatly affected by Local Station

baselines

• Constrained [All suitable stations fixed] – Fix latitude, longitude, and ellipsoid heights at Control

and Primary Base Stations

– Make sure the constraints did not distort the project

NOTE - Geoid model NOT applied at this time

BASELINE PROCESSING

• “MULTI-STATION” PROCESSING MODE

• DOUBLE DIFFERENCING (ELIMINATES SAT/RECEIVER CLOCK, HARDWARE BIASES, REDUCES NOISE PARAMETERS)

• PRECISE EPHEMERIS

• 15° CUT OFF (BUT COLLECT AT 10°)

• FIX ALL INTEGERS FOR BASELINES LESS THAN 40 KM

• USE A TROPO MODEL RATHER THAN FIELD MET DATA UNLESS PROVEN

BETTER

• USE RELATIVE TROPO SCALE PARAMETER FOR STATIONS OVER 15 KM

AND FOR LARGE INTERSTATION RELIEF

• BASELINE RMS ≤ 1.5 CM

• REDUNDANT BASELINES DIFFER BY ≤ 2.0 CM

49

http://www.ngs.noaa.gov/orbits/orbit_data.shtml

The SP3-c format was developed to allow one to put GPS, GLONASS, and Galileo satellites all in the same file, and also to give standard deviations for the satellite XYZ coordinates and clock offset at each epoch

INDEPENDENT BASELINES IN GPS

# of Baselines =

N(N-1)

2

# of Independent

Baselines =(N-1)

N = Number of receivers observing simultaneously

50

SOME PROCESSING VIEWS SOME PROCESSING VIEWS

51

STATIC PROCESSING VARIABLES TO IMPROVE SESSION POST PROCESSING

• USE OTHER REDUNDANT BASELINES •INDEPENDENT BASELINES ( N-1)- DON’T USE BAD BASELINES •PRECISE EPHEMERIS- ESPECIALLY FOR VERTICALS •CUT OFF ANGLE- DON’T CUT OUT TOO MUCH DATA •EDIT SATELLITE DATA- DISABLE NOISY SATS, DATA •REOBSERVE WITH BETTER PLANNING, HIGHER ANTENNA

52

BASELINE ADJUSTMENT SUMMARY

ADD VERIFIED VERTICAL CONTROL ONE STATION

AT A TIME TO MAKE SURE EACH BM DOES NOT

DISTORT THE ADJUSTMENT

FAIRFAX COUNTY VERTICALS USED

40 KM

53

Topography

A B

C

D

E

F

GPS-DERIVED HEIGHTS FROM GEOID03 SEPARATION

= Published NAVD88 Orthometric Height = New Control

Ellipsoid

h h

h

h

h

h

GEOID03

N N

N N N

N

Hh-N

Hh-N

Hh-N

Hh-N

Hh-N

Hh-N

Constrained Vertical Adjustment

Topography

A B

C

D

E

F

hadj

hadj hadj

hadj

ha

dj

hadj

Adjusted Ellipsoid

Ellipsoid Height Adjusted to Fit Constrained Orthometric Heights

GPS-Derived Orthometric Heights

= Published NAVD88 Orthometric Height = New Control

H

H H

H

Geoid based on Ortho Heights

GEOID12a

Ellipsoid

h h

h

h

h

h HGPS

HGPS

N N

N N N

N

GEOID12a

54

ADJUSTMENT TO PASSIVE CONTROL

Elevation published

to centimeters

Orthometric height

determined by GPS

Identified as Height Mod

survey station

55

NGS Data Sheet – GEOID12a Published NAVD88 to GPS Derived

H

- N h = 1.913 -32.024 (-33.95)

≠

-

1.913 1.931

=

NGS Data Sheet – GEOID12a Published NAVD88 to GPS Derived

H

- N h = 97.03 65.146 (-31.88)

≠

-

97.03 97.034

=

56

PROCESSING & ADJUSTMENT REQUIREMENTS SUMMARY

• RMS ELLIPSOID HEIGHTS ≤ 1.5 CM

• REPEAT BASELINES ≤ 2.0 CM

• USE TROPO MODEL (CHOSEN IN MANUFACTURER’S SOFTWARE)

• EVALUATE VERTICAL CONTROL

• USE IONO-FREE (L3) SOLUTION FOR BASELINES ≥ 5 KM

• USE L1 SOLUTION FOR ALL OTHERS

• MINIMALLY CONSTRAINED ADJUSTMENT – VERIFIES FIELD DATA CONSISTENCY

• FULLY CONSTRAINED ADJUSTMENT – PLACES PROJECT ON NAVD 88/NAD 83 PASSIVE MARKS

• GOAL IS 2 CM NAVD 88 HEIGHTS BETWEEN NETWORK MONUMENTS

POSSIBLE ALTERNATIVE = RTN APPROACH • EVALUATE GEOID MODEL ACROSS THE COUNTY

• REFINE AS NECESSARY (GEODETIC LEVELING)

• CONSTRUCT ACTIVE STREAMING STATIONS CONFORMING TO NGS GUIDELINES SPACED AT A MAXIMUM OF 50 KM

• SEED COORDINATES ON THE STATIONS WITH 10 DAYS OF OPUS-DB OR OPUS-PROJECTS SOLUTIONS

• PERFORM A LEAST SQUARES ADJUSTMENT WEIGHTING (NGS) CORS TO 1 CM IN EACH HORIZONTAL COMPONENT AND 2 CM IN THE ELLIPSOID HEIGHT

• EVALUATE RESULTS – THEY SHOULD ALL BE VERY CLOSE TO THE OPUS POSITIONS. IF THE RTN HAS A MAXIMUM DELTA BELOW 2 CM HORIZONTALLY AND 4 CM ELLIPSOID HEIGHT, THE RTN IS SUCESSFULLY ALIGNED TO THE NSRS.

• BEGIN WORK!

57

POSSIBLE FAIRFAX COUNTY RTN

USE POST FLIGHT PHOTO POINTS FOR GROUND TRUTHING

58

•Submit GPS data to OPUS – www.ngs.noaa.gov/OPUS •Processed automatically on NGS computers

•OPUS-S (2-48 hours): ties to 3 CORS or •OPUS-RS (15 minutes–2 hours): ties to <= 9 CORS

•Solution via email - in minutes •Fast, easy, consistent access to NSRS

Online Positioning User Service

(OPUS)

THE VALUE OF OPUS SAVED THIS SURVEYOR’S LICENSE AND BUSINESS! OPUS ON BENCH MARKS IS ALSO VALUABLE TO PLACE ACCURATE POSITIONS ON LOCATIONS THAT COULD BE JUST SCALED FROM TOPO MAPS. THIS AIDS IN THE MONUMENT’S RECOVERY (AND LOCATES THE BENCH MARK ACCURATELY FOR INPUT INTO THE GEOID MODELING DONE BY NGS)

59

NGS WILL PROVIDE A POSITION FOR YOUR GPS DATA VIA “OPUS”

ONLINE EXAMPLE?

Is Your OPUS-S Solution Good?

• > 90% observations used

• > 50% ambiguities fixed

• < 3 cm overall RMS

• < 5 cm peak-to-peak errors

• check antenna info

• check ephemeris type

…and which CORS were used? … resubmit later for better CORS scenario & ephemeris

60

1641.577

• 15-minute to 2-hour sessions

• ties to 3 – 9 CORS (< 250km)

• uses RSGPS vs. PAGES software

• P1/P2 code & L1/L2 phase observations

• resolves all ambiguities with LAMBDA

• similar to Real-Time Network computations

• RSGPS solution modes:

–network: solves ambiguities, tropo, iono

– rover: tropo and ion interpolated to rover

• ~10,000 lines of code

OPUS-Rapid Static (OPUS-RS)

61

OPUS-RS REFERENCE STATION SEARCH ALGORITHM

THE 28 NERRS, BEING ALONG COASTAL REGIONS, MIGHT HAVE PROBLEMS USING OPUS-RS!

62

“#Fixed Ambiguities” replaced by “Quality Indicator” •average of W-ratio (separation between candidate sets of ambiguities) of last 3 epochs •reported as network mode / rover mode •look for values > 3 for confidence in solution

NGS OPUS-RS SOLUTION REPORT USER: [email protected] DATE: October 29, 2007

RINEX FILE: 1207287x.07o TIME: 14:39:04 UTC

SOFTWARE: rsgps 1.09 RS11.prl 1.12 START: 2007/10/14 23:27:15

EPHEMERIS: igr14490.eph [rapid] STOP: 2007/10/15 00:00:15

NAV FILE: brdc2870.07n OBS USED: 1962 / 2082 : 94%

ANT NAME: ASH701975.01A QUALITY IND. 34.21/ 37.91

ARP HEIGHT: 0.0 NORMALIZED RMS: 0.307

REF FRAME: NAD_83(CORS96)(EPOCH:2002.0000) ITRF00 (EPOCH:2007.78627)

LAT: 36 2 52.79767 0.008(m) 36 2 52.81498 0.008(m)

E LON: 252 2 18.45532 0.013(m) 252 2 18.41156 0.013(m)

W LON: 107 57 41.54468 0.013(m) 107 57 41.58844 0.013(m)

EL HGT: 1974.304(m) 0.005(m) 1973.396(m) 0.005(m)

ORTHO HGT: 1995.280(m) 0.026(m) [Geoid03 NAVD88]

OPUS-RS Output

*

“Overall RMS” replaced by “Normalized RMS” •unitless quantity, “expected” = 1 •aka standard deviation of unit weight •if > 1, noisy data somewhere •typically <1, meaning noise less than expected









LAT: 36 2 52.79767 0.008(m) 36 2 52.81498 0.008(m)

E LON: 252 2 18.45532 0.013(m) 252 2 18.41156 0.013(m)

W LON: 107 57 41.54468 0.013(m) 107 57 41.58844 0.013(m)

EL HGT: 1974.304(m) 0.005(m) 1973.396(m) 0.005(m)


OPUS-RS Output

*

63

Peak-to-Peak replaced by Est. Standard Deviations •approximately 95% confidence •derived from scatter of single baseline solutions •formal standard deviations (optimistic) available in Extended Output









LAT: 36 2 52.79767 0.008(m) 36 2 52.81498 0.008(m)

E LON: 252 2 18.45532 0.013(m) 252 2 18.41156 0.013(m)

W LON: 107 57 41.54468 0.013(m) 107 57 41.58844 0.013(m)

EL HGT: 1974.304(m) 0.005(m) 1973.396(m) 0.005(m)


OPUS-RS Output

* *

OPUS-RS- COMPARING DIFFERENT TIME ON POINT SOLUTIONS

64

VARIOUS OPUS SOLUTIONS USING “CORB”

4/1/12.15M 12/1/11.15M 12/1/11.1 H 3/09/12. 1 H

4/1/12.1last RS 4/1/12. 1st4 H

4/1/12. 2nd4 H

4/1/12. 2last RS

4/1/12. 2last S

4/1/12. 1first RS

N E h H

CORB: PUBLISHED (OLD) 2060045.533 3598666.726 37.252

"CORB" REFLECTS A PERFECT SCENARIO FOR A

CORB: 8 HOURS AS "TRUTH" 2060045.532 3598666.740 37.239 POINT POSITION

SOLUTION D N D E D h NOTES

DAY 92

OPUS-S: 1ST 4 HOURS 0.000 -0.002 0.005

THESE ARE NOT INDEPENDENT OBSERVATIONS

OPUS-S: 2ND 4 HOURS 0.001 -0.002 -0.011

THEY SHOW DIFFERENCES WITH SLICING A PIECE OF

OPUS-S: 1ST 2 HOURS -0.005 -0.003 -0.005

THE PIE, AND PROCESSING WITH THE TWO PROGRAMS

OPUS-RS: 1ST 2 HOURS 0.006 -0.007 0.002 "

OPUS -S: LAST 2 HOURS -0.004 0.003 0.015 "

OPUS-RS: LAST 2 HOURS 0.004 -0.005 0.011 "

OPUS-RS: 1ST 1 HOUR 0.009 -0.008 0.008 "

OPUS-RS: LAST 1 HOUR 0.006 -0.007 -0.009 "

OPUS-RS: 15 MINUTES 0.009 -0.006 -0.005 "

SOME OPUS COMPARISONS WITH A “PERFECT” SITE

65

DAY 69

OPUS-S: 9 HOURS -0.001 -0.004 0.000 THESE ARE NOT INDEPENDENT OBSERVATIONS

OPUS-S:MID 2 HOURS 0.012 -0.010 -0.021 THEY SHOW DIFFERENCES WITH SLICING A PIECE OF

OPUS-RS: MID 2 HOURS 0.008 -0.008 0.000 THE PIE, AND PROCESSING WITH THE TWO PROGRAMS

OPUS-S: 2 HOURS -0.014 0.013 -0.003 "

OPUS-RS: 2 HOURS 0.010 -0.009 0.022 "

OPUS-RS: 1 HOUR 0.010 -0.010 0.002 "

2011 DAY 335

OPUS-RS: 15 MINUTES 0.009 -0.008 -0.005 THESE ARE NOT INDEPENDENT OBSERVATIONS

OPUS-RS: 1 HOUR 0.006 -0.008 -0.017 THEY SHOW DIFFERENCES WITH SLICING A PIECE OF

THE PIE, AND PROCESSING WITH THE TWO PROGRAMS

COMPARISON WITH 3/9/12 & 12/1/11 ASHTECH 700936E ANTENNA AT CORB

66

http://www.ngs.noaa.gov/OPUSI/Plots/Gmap/OPUSRS_sigmap.shtml

67

OPUS –DB: CREATE A POINT IN THE NGS OPUS DATABASE

• OBS USED ≥ 70%

• # FIXED AMB ≥ 70%

• OVERALL RMS ≤ 3 cm

• PEAK TO PEAK ≤ 4 cm, 8 cm ellipsoid

• DESCRIPTION

• PICTURES

http://testwww.ngs.noaa.gov/web/GoogleMaps/RTN/RTN.shtml

http://testwww.ngs.noaa.gov/web/GoogleMaps/RTN/RTN.shtml

68

OPUS – PROJECTS: PROJECT SESSION PROCESSING

VARYING LEVELS OF ACCESS NETWORK PROCESSING (REQUIRES NGS SANCTIONED

TRAINING)

69

OPUS - S • DUAL FREQUENCY DATA

• ≥ 2, ≤48 HOURS DATA

• PAGES ENGINE

• OBS USED > 90%

• # FIXED AMB > 50%

• OVERALL RMS < 3 cm

• PEAK TO PEAK < 5 cm

OPUS - RS • DUAL FREQUENCY DATA

• ≥ 15 MINUTES, ≤2 HOURS DATA

• RSGPS ENGINE

• ≥ 3, ≤ 9 CORS, 250 KM

• OBS USED > 50%

• QUALITY INDICATOR ≥ 3

• NORMALIZED RESIDUAL ≈ 1

• OBS USED ≥ 70%

• # FIXED AMB ≥ 70%

• OVERALL RMS ≤ 3 cm

• PEAK TO PEAK ≤ 4 cm, 8 cm ellipsoid

• DESCRIPTION

• PICTURES

OPUS - DB

BLUEBOOKING

USING OPUS-S OR OPUS –RS WITH REAL TIME POSITIONING FOR SMALL PROJECTS-

PERFORMED ORIGINALLY BY NCGS

71

INTER STATION DISTANCE

FROM SOFTWARE COMPUTATION

INTER STATION DISTANCE

POSSIBLE “TRUE” DISTANCE

HORIZONAL ERROR ELLIPSE FROM COOVARIANCE

± 1.15 CM ± 1.05 CM

1.

2.

EXAMPLE: SAY DISTANCE 1. = 110.000’ SAY DISTANCE 2. = 110.065’ ERROR = 1 IN 1692 ± IMPORTANCE: EVEN HOLDING JUST 0NE COORDINATE AS TRUTH, AND NOTING THERE WOULD BE NO ANGULAR ERROR, TRAVERSE LOOPS AND/OR LOCATIONS RUN FROM THIS COORDINATE PAIR START WITH A GROSS ERROR. IF INTER STATION DISTANCE WAS 1100’, THE ERROR IS REDUCED BY AN ORDER OF MAGNITUDE (1 IN 17000 ±).


± 1.15 CM ± 1.05 CM

INTER STATION DISTANCE & DIRECTION



± 1.15 CM ± 1.05 CM

1.

2.


± 1.15 CM ± 1.05 CM

EXAMPLE: SAY DISTANCE 1. = 110.000’ SAY DISTANCE 2. = 110.004’ ERROR = 1 IN 27500 ± IMPORTANCE: EVEN THOUGH THE INTER STATION DISTANCE IS ACCEPTABLE HERE, THE ANGULAR ERROR WOULD BE OVER 2 MINUTES. TRAVERSE LOOPS OR OPTICAL LOCATIONS, STARTING FROM THS POINT PAIR, START WITH A GROSS ERROR. IF INTER STATION DISTANCE WAS 1100’, THE ERROR IS REDUCED TO 12 SECONDS.

72

VERTICAL PRECISION @ 1.5 CM (0.047’) AT ONE SIGMA = 3.0 CM (0.093’) AT 2 SIGMA OR 95% CONFIDENCE. THESE ERRORS ARE NOT DISTANT DEPENDENT EXCEPT TO AFFECT THE VERTICAL ANGLE BETWEEN STATIONS AND ADD SOME ERROR TO THE INTERSTATION DISTANCE.

INTER STATION ELEVATION DIFFERENCE


RECOMMENDATIONS FOR GNSS POINT PAIRS AS SITE CONTROL

• HOLD THE STATION WITH THE SUNNIEST SOLUTION STATISTICS AS “TRUTH” FOR HORIZONTAL . DITTO FOR THE VERTICAL (MAY NOT BE THE SAME POINT).

• SET POINT PAIR AS FAR APART AS POSSIBLE, WITH OPEN SKY – EVEN IF A P.O.L. IS NECESSARY FOR THE SITE WORK.

• USE THE INVERSE BETWEEN THE STATIONS FOR AN AZIMUTH, BUT OCCUPY THE STAION WITH THE HELD COORDINATES.

• REDUNDANT OPUS SOLUTIONS AND USING BOTH OPUS-S AND OPUS-RS WILL ADD TO CONFIDENCE AND ENABLE TWEAKING THE COORDINATES.

73

•INTERNET DATA VIA CELL TECHNOLOGY •SOFTWARE/FIRMWARE ALGORITHMS •GNSS HARDWARE •SATELLITE CONSTELLATIONS •SATELLITE CODES/FREQUENCIES

THE USE OF RTK IN SITE CONTROL - A CONFLUENCE OF TECHNOLOGY THE IMPORTANCE OF INTELLIGENT RT FIELD WORK

- Multipath - Position Dilution of Precision (PDOP) - Baseline Root Mean Square (RMS) - Number of satellites - Elevation mask (or cut-off angle) - Base accuracy- datum level, local level - Base security - Redundancy, redundancy, redundancy - Part(s) Per Million Error (ppm) – iono, tropo models, orbit errors - Space weather- sunspot numbers, solar maximum - Geoid quality - Site calibrations (a.k.a. Localizations) - Bubble adjustment - Latency, update rate - Fixed and float solutions - Accuracy versus Precision - Signal to Noise Ratio (S/N or C/N0) - Carrier phase solution - Code phase solution - VHF/UHF radio communication - CDMA/SIM/Cellular TCP/IP communication -WGS 84/ITRF00/IGS08/NAD 83, & Local datums - GPS, GLONASS, Galileo, Compass Constellations

THE CONTROL IS AT THE POLE!

74

THE THREE BASE STATION OPTIONS FOR RT REAL TIME GNSS GUIDELINES

http://www.ngs.noaa.gov/PUBS_LIB/NGS.RTN.Public.v2.0.pdf




75

NGS SINGLE BASE GUIDELINES


• 4 CLASSES OF PRECISION (ACCURACY TO BASE) • BEST METHODS FOR FIELD DATA COLLECTION • BACKGROUND INFO. FOR RTK • RTK GLOSSARY • SUMMARY CHAPTER • APPENDICES (INCLUDING LDP INFO.)

RTN GUIDELINES FOR GNSS POSITIONING–

WILL NOT SPECIFY OR DEFINE A STANDARD, BUT

WILL HELP ADMINISTRATORS AND

USERS TO BE AWARE OF ALL THE ISSUES INVOLVED WITH

THIS NEW TECHNOLOGY

60+ CONTRIBUTORS:

•NGS ADVISORS •DOT

•STATE GEODETIC SURVEYS

•GNSS MANUFACTURERS •SRCs

•BLM, NPS

http://www.ngs.noaa.gov/PUBS_LIB/NGS.RTN.Public.v2.0.pdf

76

“CONFIDENCE” IN YOUR

POSITION INCREASES

WITH:

• MORE SATELLITES

• SHORTER BASELINES

• LOWER ‘DOP’

• MORE OPEN SKY

• LOWER RMS

• CONTINUOUS COMMUNICATION

• REDUNDANCY, REDUNDANCY, REDUNDANCY

The best of all single base worlds: 8 GPS satellites, GDOP 1.5, 2 km baseline, RMS ≤ 0.01 m, open sky, no weather elements, solid communication, no multipath

FOR RTN LOOK FOR: GDOP ≤ 3 (or PDOP ≤ 2.5) Number of GPS satellites ≥7 Time on point = 5 second record intervals for 1 minute Position RMS ≤ 0.02 m horizontal, 0.04 vertical (ellipsoidal). Redundancy ≥ 2 locations staggered by 4 hours. Redundant locations must differ no more than the desired point accuracy from the average of the coordinates as located.

RT USER GUIDELINES

77

MULTIPATH

θ

θ

= EXTRA DISTANCE

78

RT FOR SITE CONTROL ADVANTAGES: • LESS TIME- SECONDS ON POINT • LESS LABOR- NO POST PROCESSING, MINIMAL PERSONNEL • LESS EQUIPMENT – ONLY ONE RT UNIT NECESSARY WITH RTN • = LESS $$$ • USER KNOWS POSITION HAS BEEN CAPTURED AT REQUIRED PRECISION • “GOOD” RELATIVE PRECISION IN HOMOGENEOUS TERRAIN AND USING THE SAME INITIALIZATION • NEW GEOPOTENTIAL DATUM WILL BE ACCESSED THROUGH ACTIVE STATIONS DISADVANTAGES: • LESS ACCURACY THAN LEVELING OR STATIC GNSS • REQUIRES ADEQUATE USER KNOWLEDGE OF ALL EFFECTS ON RT GNSS POSITIONING

RTK VS. RTN

RTK

RTN Plus:

Easy alignment to the NSRS No ppm (1ST ORDER) ERROR

Extended range Homogeneous Data Easy datum updates

Cell technology

-Half the equipment or double the production -No monument reconnaissance/ recovery - No set/break down time -No base baby sitting

79

•WHAT DATUM IS THE RTN USING? •WHAT ADJUSTMENT OF THE DATUM IS THE RTN USING? •WHAT EPOCH OF THE DATUM ADJUSTMENT IS THE RTN USING? •HOW DOES THE RTN ALIGN TO THE NSRS? •CAN USERS USE ANY MANUFACTURERS’ EQUIPMENT IN THE RTN? •DO OVERLAPPING NETWORKS GIVE THE SAME COORDINATES? •WHAT ARE THE FIELD ACCURACIES?

USERS CONCERNS WITH RTN SO – WHAT CAN I EXPECT FROM AN RTN?

MOST RTN PRODUCE “GOOD” HORIZONTAL VALUES – TO A FEW CM. OUR HORIZONTAL SYSTEM IS BASED ON ACTIVE REFERENCE STATIONS (NGS CORS), AS ARE THE RTN STATIONS. BECAUSE ORTHOMETRIC HEIGHTS (‘ELEVATIONS’) ARE BASED ON PASSIVE MONUMENTS WITH NAVD 88, THE RTN USER SHOULD, FOR THE MOST PART, CONSTRAIN THE PASSIVE MARK VALUES IN A LOCALIZATION. CHOOSE THE RTN WITH A BUSINESS MODEL THAT BEST FITS YOUR NEEDS. RTK FROM A BASE ON SITE HELD AS “TRUTH” IS USUALLY SUPERIOR TO AN RTN.

80

REAL-TIME CHOICES - BIG PICTURE ISSUES

• PASSIVE / ACTIVE – WHAT IS ‘TRUTH’?

• GEOID + ELLIPSOID / LOCALIZE – QUALITY OF GEOID MODELS LOCALLY. ORTHOMETRIC HEIGHTS ON CORS?

• GRID / GROUND – LOW DISTORTION PROJECTIONS- SHOULD NGS PLAY?

• ACCURACY / PRECISION- IMPORTANCE OF METADATA

• SINGLE SHOT / REDUNDANCY

• RTK / RTN

• NATIONAL DATUMS / LOCAL DATUMS / ADJUSTMENTS- DIFFERENT WAYS RTN GET THEIR COORDINATES-VARIOUS OPUS, OPUS-DB, CORS ADJUSTED, PASSIVE MARKS. VELOCITIES - NEW DATUMS, “4 -D” POSITIONS

• GNSS / GPS

“CONFIDENCE” IN YOUR

POSITION INCREASES

WITH:

• MORE SATELLITES

• SHORTER BASELINES

• LOWER ‘DOP’

• MORE OPEN SKY

• LOWER RMS

• CONTINUOUS COMMUNICATION

• REDUNDANCY, REDUNDANCY, REDUNDANCY

The best of all single base worlds: 8 GPS satellites, GDOP 1.5, 2 km baseline, RMS ≤ 0.01 m, open sky, no weather elements, solid communication, no multipath

FOR RTN LOOK FOR: GDOP ≤ 3 (or PDOP ≤ 2.5) Number of GPS satellites ≥7 Time on point = 5 second record intervals for 1 minute Position RMS ≤ 0.02 m horizontal, 0.04 vertical (ellipsoidal). Redundancy ≥ 2 locations staggered by 4 hours. Redundant locations must differ no more than the desired point accuracy from the average of the coordinates as located.

81

• B BUBBLE- ADJUSTED?

• RT BATTERY- BASE FULLY CHARGED 12V?

• B BATTERY – ROVER SPARES?

• RT USE PROPER RADIO CABLE (REDUCE SIGNAL LOSS)

• RT RADIO MAST HIGH AS POSSIBLE? (5’ = 5 MILES, 20’ = 11 MILES, DOUBLE HEIGHT=40% RANGE INCREASE). LOW LOSS CABLE FOR >25’.

• RT DIPOLE (DIRECTIONAL) ANTENNA NEEDED?

• RT REPEATER?

• RT CABLE CONNECTIONS SEATED AND TIGHT?

• B“FIXED HEIGHT” CHECKED?

• RT BASE SECURE?

• RT UHF FREQUENCY CLEAR?

• B CDMA/CELL - STATIC IP FOR COMMS?

• B CONSTANT COMMS WHILE LOCATING

• RT BATTERY STRENGTH OK?

• B CELL COVERAGE?

• B KEEP FIRMWARE UPDATED!

82

• RT WEATHER CONSISTENT?

• B CHECK SPACE WEATHER?

• B CHECK PDOP/SATS FOR THE DAY?

• RT OPEN SKY AT BASE?

• RT MULTIPATH AT BASE?

• B MULTIPATH AT ROVER?

• B USE BIPOD?

DUAL CONSTELLATION RT POSSIBILITIES: GPS ≥ 5, GLN = 0 GPS = 4, GLN = 2 GPS = 3, GLN = 3 GPS = 2, GLN = 4 (Can't initialize with only GLN Sats.)

3

• B ≥ 4 H & V, KNOWN & TRUSTED POINTS?

• B LOCALIZATION RESIDUALS-OUTLIERS?

• B DO ANY PASSIVE MARKS NEED TO BE

HELD?

• RT BASE WITHIN CALIBRATION (QUALITY

TIE TO NEAREST CALIBRATION POINT)?

• B SAME OFFICE & FIELD CALIBRATION

USED?

FYI: GNSS CAN PROVIDE GOOD RELATIVE POSITIONS IN A PROJECT WHILE STILL NOT CHECKING TO KNOWNS IN AN ABSOLUTE SENSE

83

• B TRUSTED SOURCE?

• B WHAT DATUM/EPOCH ARE NEEDED?

• RT GIGO

• B ALWAYS CHECK KNOWN POINTS.

• B PRECISION VS. ACCURACY

• B GROUND/PROJECT VS. GRID/GEODETIC

• B GEOID MODEL QUALITY

• B LOG METADATA

AUTONOMOUS LOCAL BASE STATION POSITION ARE

OK IF CORRECT COORDINATES ARE INTRODUCED IN THE PROJECT FIRMWARE/SOFTWARE LATER

• B CHECK ON KNOWN POINTS AT START OF SESSION!

• B SET ELEVATION MASK

• B ANTENNA TYPES ENTERED OK?

• B SET COVARIANCE MATRICES ON (IF NECESSARY).

• B RMS SHOWN IS TYPICALLY 68% CONFIDENCE (BRAND DEPENDENT)

• B H & V PRECISION SHOWN IS TYPICALLY 68% CONFIDENCE

• B TIME ON POINT? QA/QC OF INTEGER FIX

• B MULTIPATH? DISCRETE/DIFFUSE

• B BUBBLE LEVELED?

• B PDOP?

• B FIXED SOLUTION?

• B USE BIPOD?

• B COMMS CONTINUOUS DURING LOCATION?

• B BLUNDER CHECK LOCATION ON IMPORTANT POINTS.

84

• B CHECK KNOWN BEFORE, DURING, AFTER SESSION. COMPARE POSITIONS WITH/WITHOUT GLONASS.

• B NECESSARY REDUNDANCY? (U. of Newcastle)

• B WHAT ACCURACY IS NEEDED?

• RT REMEMBER PPM

• RT BASE PRECISION TO NEAREST CALIBRATION POINT

• B AVERAGE REDUNDANT SHOTS – PRECISION DIFFERENCE WITHIN NEEDS OF SURVEY

• B BE AWARE OF POTENTIAL INTERFERENCE (E.G., HIGH TENSION TOWER LINES)

CAN’T INITIALIZE? BAD CHECKS? PLENTY OF SATS? TRY: TURN OFF GLONASS IF YOU HAVE ≥6 COMMON GPS SATS REININTIALIZE CHECK FOR “NOISY” SATS IN DATA COLLECTOR LOOK FOR MULTIPATH NEARBY ALSO-COMPARE GNSS POSITION TO GPS ONLY POSITION

Comparison of 30 Minute Solutions - Precise Orbit; Hopfield (0); IONOFREE

(30 Minute solutions computed on the hour and the half hour)

MOLA to RV22 10.8 Km

Day 264dh

(m)

Hours

Diff.Day 265

dh

(m)

Day 264

minus

Day 265

(cm)

*

diff

>2

cm

Mean dh

(m)

Mean dh

minus

"Truth"

(cm)

*

diff

>2

cm

14:00-14:30 -10.281 27hrs 17:00-17:30 -10.279 -0.2 -10.280 -0.5

14:30-15:00 -10.278 27hrs 17:30-18:00 -10.270 -0.8 -10.274 0.2

15:00-15:30 -10.281 27hrs 18:00-18:30 -10.278 -0.3 -10.280 -0.4

15:30-16:00 -10.291 27hrs 18:30-19:00 -10.274 -1.7 -10.283 -0.7

16:00-16:30 -10.274 27hrs 19:00-19:30 -10.274 0.0 -10.274 0.2

16:30-17:00 -10.287 27hrs 19:30-20:00 -10.276 -1.1 -10.282 -0.6

17:00-17:30 -10.279 27hrs 20:00-20:30 -10.261 -1.8 -10.270 0.6

17:30-18:00 -10.270 27hrs 20:30-21:00 -10.251 -1.9 -10.261 1.5

18:00-18:30 -10.277 21hrs 15:00-15:30 -10.270 -0.7 -10.274 0.2

18:30-19:00 -10.271 21hrs 15:30-16:00 -10.276 0.5 -10.274 0.2

19:00-19:30 -10.277 21hrs 16:00-16:30 -10.278 0.1 -10.278 -0.2

19:30-20:00 -10.271 21hrs 16:30-17:00 -10.286 1.5 -10.279 -0.3

20:00-20:30 -10.259 18hrs 14:00-14:30 -10.278 1.9 -10.269 0.7

20:30-21:00 -10.254 18hrs 14:30-15:00 -10.295 4.1 * -10.275 0.1

"Truth"

14:00-21:00 -10.275 14:00-21:00 -10.276 0.1 -10.276

Two Days/Same Time

-10.254

-10.251 > -10.253

Difference = 0.3 cm

“Truth” = -10.276

Difference = 2.3 cm

Two Days/

Different Times

-10.254 -10.295 > -10.275

Difference = 4.1 cm

“Truth” = -10.276

Difference = 0.1 cm

THE IMPORTANCE OF REDUNDANCY

85

FURTHER WORK IN THE OFFICE

•Antenna heights (height blunders are unacceptable and can even produce horizontal error - Meyer, et.al, 2005). •Antenna types •RMS values •Redundant observations •Horizontal & vertical precision •PDOP •Base station coordinates •Number of satellites •Calibration (if any) residuals

VECTOR & EQUIPMENT REVIEW

86

BESIDES ATTRIBUTE FIELDS, THE RT PRACTICIONER MUST KEEP RECORDS OF ITEMS NOT RECORDED IN THE FIELD, FOR INSTANCE: WHAT IS THE SOURCE OF THE DATA? WHAT WAS THE DATUM/ADJUSTMENT/EPOCH? WHAT WERE THE FIELD CONDITIONS? WHAT EQUIPMENT WAS USED, ESPECIALLY- WHAT

ANTENNA? WAS COMMUNICATION SOLID? WHAT FIRMWARE WAS IN THE RECEIVER &

COLLECTOR? WERE ANY GUIDELINES USED FOR COLLECTION? WHAT REDUNDANCY, IF ANY, WAS USED? WERE ANY PASSIVE MARKS CONSTRAINED?

(GOOD IDEA TO CREATE A TABLULAR CHECK LIST FORM)

QUICK FIELD SUMMARY:

•Set the base at a wide open site

•Set rover elevation mask between 12° & 15° •The more satellites the better •The lower the PDOP the better •The more redundancy the better •Beware multipath •Beware long initialization times •Beware antenna height blunders •Survey with “fixed” solutions only •Always check known points before, during and after new location sessions •Keep equipment adjusted for highest accuracy •Communication should be continuous while locating a point •Precision displayed in the data collector can be at the 68 percent level (or 1σ), which is only about half the error spread to get 95 percent confidence •Have back up batteries & cables •RT doesn’t like tree canopy or tall buildings

87

THE QUICK SUMMARY BOILED DOWN: FOUR CARDINAL RULES FOR USING RT FOR

PROJECT CONTROL

PROJECT CONTROL SUMMARY

• KNOW WHAT IS “TRUTH” FOR YOUR PROJECT (E.G., LEGACY CONTROL, OLD PLANS VS. OPUS SOLUTIONS, RTN DERIVED DATA). REMEMBER OPUS USES NAD 83 (2011).

• RECOMMEND SURVEYORS USE STATIC GNSS FOR LARGE PROJECTS, CORRIDOR SURVEYS, PROJECTS WITH FUTURE EXPANSION AREAS.

• LOCALIZING TO THE EXISTING CONTROL AROUND A PROJECT CAN SHOW THE PRECISION OF HOW THE CONTROL INTERRELATES.

• KEEP GOOD METADATA RECORDS – ESPECIALLY FOR RT WORK

• REDUNDANCY INCREASES CONFIDENCE WITH YOUR DATA AND HIGHLIGHTS OUTLIERS.

• BE CONSCIOUS OF GRID/GROUND ISSUES

• SET NEW PROJECT CONTROL FOR OPTICAL SURVEY WORK AS FAR APART AS PRACTICAL

Bill Henning, PLS. · 2018-04-04 · • remote sensing and mobile mapping . 2...

Documents

Transcript of Bill Henning, PLS. · 2018-04-04 · • remote sensing and mobile mapping . 2...