WHAT WILL GNSS BE LIKE IN TEN YEARS?

Transcription

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 1

2 POSITIONING TECHNOLOGY- A CARTOON GRAPH 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 STICKS AND STRINGS THE CHANGE FROM LABOR INTENSIVE TO TECHNOLOGY! COMPASS THEODOLITE GNSS- GLONASS, GALILEO, COMPASS/BEIDOU, INDOOR POSITIONING, CM PPP GIS RTN GPS RTK TOTAL STATION RTX 0.5' SAT IMAGERY, MOBILE TERR. LASER SCANNING, 0.10' AERIAL MAPPING, INTERNATIONAL NETWORKS, 24/7/365 SAT. COVERAGE TECHNOLOGY WHAT WILL GNSS BE LIKE IN TEN YEARS? YEAR 2

3 GNSS GPS GLONASS GALILEO COMPASS (BEIDOU-2) 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, 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. 3

4 GPS AND GLN GNSS CONSTELLATIONS DUAL CONSTELLATION RT POSSIBILITIES: GPS 5, GLN = 0 BEST SCENARIO = 7 OR MORE GPS GPS = 4, GLN = 2 GLN K SATS WILL HAVE A CDMA (L3) GPS = 3, GLN = 3 FORMAT SIGNAL GPS = 2, GLN = 4 (Can't initialize with only GLN Sats.) 4

5 GPS LAUNCH HISTORY GLONASS STATUS 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. 5

6 GALILEO- OFF THE GROUND OCTOBER 21, IOV SATELLITES, EUROPEAN SPACEPORT, FRENCH GUIANA, RUSSIAN SOYEZ ROCKET (SPUTNIK, YURI GREGARIN) THE NATIVE CONDITION OF THE GNSS SIGNAL EVERY EPOCH OF OBSERVATION MUST COMPUTE CHANGE IN POSITION DUE TO EARTH ROTATION, SATELLITE ORBIT CHANGE AND RELATIVITY! AT LEAST 22 SATELLITES UNDER CONTRACT (27 PLUS 3 SPARES PLANNED) AT C, 1 NANOSECOND = 30 CM! CORRECTIONS TO SVN S clocks before launch: S.R.= +7 μ sec., G.R = μ sec. = -38 μ sec./ day! 6

7 THE INTEGER AMBIGUITY Resolving the integer ambiguity allows phase measurements to be related to distances Dl = First Partial Wavelength Nl = Integer Ambiguity WGS 84 X,Y,Z THE AMBIGUITY SEARCH. 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) Distance = Nl + Dl RESOLUTION TO ROUGHLY 2 mm λ1 = cm 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. λ2 = cm λ5 = cm 7

8 SUNSPOT CYCLE EFFECTS IN THE IONOSPHERE IONO & TROPO LAYERS AND THEIR EFFECT ON THE GNSS SIGNAL 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

9 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 troposphere ORBITAL ERRORS CONTRIBUTING TO PPM ERRORS 1 cm! POST PROCESSED 2-5 m USED IN RTK (SOME RTN CAN USE ULTRA-RAPID ORBITS) AFFECTS VERTICAL MORE TRHAN HORIZONTAL (See user guidelines references for Graphic: Ahn, 2005) 9

10 THE CYCLE COUNT COOKBOOK- USING DIFFERENCING TO ELIMINATE OR REDUCE COMMON ERRORS IN THE RECEIVER AND SATELLITE 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 RECEIVER HARDWARE DELAYS SATELLITE HARDWARE DELAYS RECEIVER CLOCK BIAS SATELLITE CLOCK BIAS IONO DELAY TROPO DELAY MEASUREMENT NOISE (HIGHER GRADE RECEIVERS = LESS NOISE) MULTIPATH ELIMINATED WITH DIFFERENCING SAME AS BASE WITH SINGLE BASE INTERPOLATED WITH RTN NOT ELIMINATED WITH DIFFERENCING 10

11 SINGLE DIFFERENCE OR MODELED BY RTN 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 11

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. 12

13 DOUBLE DIFFERENCE TRIPLE DIFFERENCING = difference between two single differences of two receivers and TWO satellites at the same epoch Triple difference difference of two double differences at two epochs for two satellites and two receivers. Detects cycle slips 13

14 TRIPLE DIFFERENCE SOME INTEGER FIXING TECHNIQUES (FOR RTK, DUAL FREQUENCY ALSO ENABLES OTF INITIALIZATION) Wide Laning (L1 L2) = c (speed of light) ( MHz MHz) or 299, Km/sec MHz = m wave length. Narrow Laning (L1 + L2) = c (speed of light) ( MHz MHz) or 299, Km/sec MHz = m wave length Iono Free f(l 1 )ion-free = a 1.f(L 1 ) + a 2.f(L 2 ) with a 1 = f 1 2/ (f f 2 2 ) and a 2 = - f 1. f 2 /(f f 2 2 ) Cancels Double Difference integer cycles Triple Differencing Kalman Filtering Double Differencing 14

15 INTEGER SEARCH TO GET TO THE BOTTOM LINE.. SURVEYORS GEODESISTS 15

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 16

17 200 RTN WORLDWIDE 80 RTN USA 37 DOT MAJOR RTN IN THE USA (JAN 2013) ACADEMIC/SCIENTIFIC SPATIAL REFERENCE CENTERS VARIOUS DOTS + MACHINE GUIDANCE COUNTY CITY GEODETICSURVEYS(NC,SC) MANUFACTURERS VENDOR NETWORKS AGRICULTURE MA & PA NETWORKS 17

18 STAND ALONE POSITIONING IN CENTIMETERS: RTX KNOWING DATUMS AND PROJECTIONS CAN HELP WITH ANALYZING ERRORS GPS IS MAINTAINED BY THE DoD IN WGS 84 GLONASS IS MAINTAINED IN PZ 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 18

19 DATUM DEFINITIONS IN THE USA SILVER SPRING, MD HORIZONTAL/ GEOMETRIC: NAD 83- USA VERTICAL/GEOPOTENTIAL: NGVD 29 ITRF 2000 ITRS- OLD CORS/WORLD WGS 84- GPS (DoD) NAVD 88 NAVD 22 (?) NAD 83 IGS 08 NEW CORS PROJECTIONS FROM DATUMS: SPC NRS 22 (?) NEW GEOCENTRIC UTM LDP 19

20 NAD 83 VELOCITIES (GOLD) SANTA CRUZ, CA ITRF 2000 VELOCITIES (BLUE) 20

21 MOVE GEOCENTER TO SOME EPOCH OF IGS FIXED ON NORTH AMERICAN PLATE? ASSIGN VELOCITIES TO THE STATIONS ACCESSED THROUGH THE CORS NETWORK NEW NATIONAL VERTICAL DATUM:2022(?) WHY ISN T NAVD 88 GOOD ENOUGH ANYMORE? 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) RE-LEVELING WOULD COST 200 MILLION TO 2 BILLION $$ 21

22 WHAT ABOUT THE PASSIVE MARKS? SECONDARY ACCESS (USE AT YOUR OWN RISK) 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) 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 22

23 WHAT ABOUT CONVERTING TO/FROM NAVD 88? NAVD 88 CONVERSION TO NEW DATUM Importance of Vertical Datums and Water Levels to Shoreline Property AL, AK, CA, CT, FL, GA, LA, MD, MS, NJ, NY, NC, OR, RI, SC, WA Privately Owned Uplands State Owned Tidelands Territorial Seas Contiguous Zone A CONVERSION WILL BE PROVIDED BETWEEN NAVD 88 AND THE NEW DATUM State Submerged Lands Exclusive Economic Zone Federal Submerged Lands 3 n. mi. High Seas ONLY WHERE RECENT GNSS ELLIPSOID HEIGHTS EXIST TO PROVIDE MODERN HEIGHTS IN THE NEW DATUM MHHW MHW MLLW 12 n. mi. 200 n. mi. Chart Datum IN MARYLAND NAVD 88 TO NVD 22 ~ 1.1 Privately Owned TX State Owned Privately Owned State Owned DE, MA, ME, NH, PA, VA 46 23

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, $$ TERRESTRIAL LASER SCANNING PROJECT SITES ONLY, H, 0.02 V, $$ MOBILE MAPPING SYSTEMS (MMS) H, 0.04 V, $$$ 24

25 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 HEIGHT MODERNIZATION- BACKGROUND EXPECTED HEIGHT MOD ACCURACIES GPS-Derived Ellipsoid Heights 1.5 centimeters (following NOS NGS-58 Guidelines) NOAA Technical Memorandum NOS NGS-58 Height Modernization -faster -cheaper -Nearly as good 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 differential leveling CHA CHING $$$$$$$ GNSS Leveling-Derived Heights Less than 1 cm in 10 km for third-order leveling = FIXED 25

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 26

27 GNSS TO A LOCAL DATUM TO A PROJECTION 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 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. 27

28 THREE SURFACES COLORADO DOT AND MODIFIED STATE PLANE Normal to ellipsoid 28

29 FOUR SURFACES SPC GRID NORTH MODIFIED SPC- DOES NOT REDUCE CONVERGENCE ANGLE OR MINIMIZE DISTORTION COMBINED FACTOR 29

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

31 DEFINING LDP 1.Define the project area and choose a representative ellipsoid height (h o ). 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 h o. Use the formula: k o = 1 + (h o / R E ), where k o = scale at projection axis, R E = 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 k o 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 k o 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: MICHAEL.DENNIS@NOAA.GOV OR altimeuserguidelines.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) 31

32 PROJECT PLANNING THOUGHTS 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 32

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? REAL TIME? BEST POSITIONING FASTEST INTEGRATED ADJUSTMENT ADEQUATE POSITIONING FOR MULTPLE STATONS USER MUST BE AWARE OF EASY CONTROL DATA FIELD PROCEDURES CAPTURE USE RT IF THE SITE IS TO CAN PROVIDE 2 CM BE CALIBRATED ORTHO HEIGHTS RTN CAN GIVE NATIVELY TAKES LONGER INADEQUATE NEED TO PROCESS DATA ORTHOMERIC HEIGHTS IF DONE IN HOUSE (BUT USUALLY OPUS-S & OPUS-RS GIVE HORIZONTAL POSITIONS POINT POSITIONS, NOT ARE GOOD) INTEGRATED ADJUSTMENT LESS METADATA 33

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 NEW PROJECT CONTROL ACCESS TO NSRS RTN ALIGNED TO CORS AT 1 CM IN EACH COMPONENT (X,Y,Z) & 2 CM ORTHOMETRIC NEW PROJECT CONTROL EXISTING PASSIVE BENCH MARKS EXISTING PASSIVE MARKS- HORIZONTAL WITH OR WITHOUT VERTICAL NATIONAL CORS = GEOMETRIC & GEOPOTENTIAL TRUTH 34

35 EXPECTED PRECISIONS FROM VARIOUS GNSS POSITIONING METHODS 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 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 35

36 USING NAD 83 ELLIPSOID HEIGHTS WITH THE HYBRID GEOID FOR ORTHO HEIGHTS H 88 = h 83 N 12a 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 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: USGG CONVERSION SURFACE = GEOID12a 72 36

37 4 HYBRID GEOID MODELS ACROSS BALTIMORE COUNTY, MD 37

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. 38

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. 39

40 PRECISION vs. ACCURACY LARGE PROJECTS USING STATIC GNSS ACCURATE NOT PRECISE NOTE: SPREAD OF SOLUTION REFLECTED IN THE RMS. HIGH RMS DOES NOT NECESSARILY MEAN A BAD RESULT PRECISE NOT ACCURATE 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 CM & 5 CM STANDARDS KEY TRUTH ACCURATE AND PRECISE U.S. DEPARTMENT OF National Oceanic and National Ocean National Geodetic COMMERCE Atmospheric Administration Service Survey 40

41 Network / Local Accuracy GPS ELLIPSOID HEIGHT HIERARCHY CORS HARN/Control Stations (75 km) Primary Base (40 km) NSRS Secondary Base (15 km) Local Network Stations (7 to 10 km) 41

42 A LOOK AT STATIC GNSS POSITIONING EXAMPLE: FAIRFAX COUNTY, VA: HTMOD PROJECT & NEW NAVD 88 ORTHOMETRIC HEIGHTS: PLANNING OBSERVATION PROCESSING ADJSTMENT 42

43 SATELLITES/ DOP WITH OBSTRUCTIONS SATELLITES/ DOP WITH OBSTRUCTIONS 43

44 SWPC WARNING 44

45 OBSERVATION PLANNING: HTMOD SESSIONS TO CONNECT CLOSEST NEIGHBORS ESTABLISH A STABLE ECCENTRIC POINT AND TRANSFER THE ORTHOMETRIC HEIGHT USING PROPER LEVELING TECHNIQUES Bench Mark G

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 46

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 47

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 48

49 INDEPENDENT BASELINES IN GPS 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 # of Baselines = N(N-1) 2 # of Independent Baselines =(N-1) N = Number of receivers observing simultaneously 49

50 SOME PROCESSING VIEWS SOME PROCESSING VIEWS 50

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 51

52 BASELINE ADJUSTMENT SUMMARY FAIRFAX COUNTY VERTICALS USED ADD VERIFIED VERTICAL CONTROL ONE STATION AT A TIME TO MAKE SURE EACH BM DOES NOT DISTORT THE ADJUSTMENT 40 KM 52

53 GPS-DERIVED HEIGHTS FROM GEOID03 SEPARATION D Constrained Vertical Adjustment Ellipsoid Height Adjusted to Fit Constrained Orthometric Heights GPS-Derived Orthometric Heights D A H h-n h N B h H h-n N C h H h-n N H h-n h N E Topography F H h-n h H h-n h Ellipsoid N N C B A h h H H h h H H GPS h adj h adj h adj h adj N N N N H GPS E h adj N h Topography F Ellipsoid Adjusted Ellipsoid H h h a dj N GEOID03 GEOID12a GEOID12a = Published NAVD88 Orthometric Height = New Control Geoid based on Ortho Heights = Published NAVD88 Orthometric Height = New Control 53

54 ADJUSTMENT TO PASSIVE CONTROL Identified as Height Mod survey station Elevation published to centimeters Orthometric height determined by GPS 54

55 NGS Data Sheet GEOID12a Published NAVD88 to GPS Derived NGS Data Sheet GEOID12a Published NAVD88 to GPS Derived H = h - N = (-33.95) H = h - N = (-31.88)

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! 56

57 POSSIBLE FAIRFAX COUNTY RTN USE POST FLIGHT PHOTO POINTS FOR GROUND TRUTHING 57

58 Online Positioning User Service (OPUS) Submit GPS data to 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 - in minutes Fast, easy, consistent access to NSRS 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) 58

59 NGS WILL PROVIDE A POSITION FOR YOUR GPS DATA VIA OPUS Is Your OPUS-S Solution Good? check ephemeris type > 90% observations used > 50% ambiguities fixed < 3 cm overall RMS check antenna info ONLINE EXAMPLE? < 5 cm peak-to-peak errors and which CORS were used? resubmit later for better CORS scenario & ephemeris 59

60 OPUS-Rapid Static (OPUS-RS) 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 60

61 OPUS-RS REFERENCE STATION SEARCH ALGORITHM THE 28 NERRS, BEING ALONG COASTAL REGIONS, MIGHT HAVE PROBLEMS USING OPUS-RS! 61

62 OPUS-RS Output NGS OPUS-RS SOLUTION REPORT USER: DATE: October 29, 2007 RINEX FILE: x.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: brdc n OBS USED: 1962 / 2082 : 94% ANT NAME: ASH A QUALITY IND / ARP HEIGHT: 0.0 NORMALIZED RMS: * REF FRAME: NAD_83(CORS96)(EPOCH: ) ITRF00 (EPOCH: ) LAT: (m) (m) E LON: (m) (m) W LON: (m) (m) EL HGT: (m) 0.005(m) (m) 0.005(m) ORTHO HGT: (m) 0.026(m) [Geoid03 NAVD88] OPUS-RS Output NGS OPUS-RS SOLUTION REPORT USER: william.stone@noaa.gov DATE: October 29, 2007 RINEX FILE: x.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: brdc n OBS USED: 1962 / 2082 : 94% ANT NAME: ASH A QUALITY IND / ARP HEIGHT: 0.0 NORMALIZED RMS: REF FRAME: NAD_83(CORS96)(EPOCH: ) ITRF00 (EPOCH: ) LAT: (m) (m) E LON: (m) (m) W LON: (m) (m) EL HGT: (m) 0.005(m) (m) 0.005(m) ORTHO HGT: (m) 0.026(m) [Geoid03 NAVD88] * #Fixed Ambiguities replaced by Quality Indicator average of W-ratio (separation between candidate of last 3 epochs reported as network mode / rover mode look for values > 3 for confidence in solution sets of ambiguities) 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 62

63 OPUS-RS Output NGS OPUS-RS SOLUTION REPORT USER: DATE: October 29, 2007 RINEX FILE: x.07o TIME: 14:39:04 UTC OPUS-RS- COMPARING DIFFERENT TIME ON POINT SOLUTIONS 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: brdc n OBS USED: 1962 / 2082 : 94% ANT NAME: ASH A QUALITY IND / ARP HEIGHT: 0.0 NORMALIZED RMS: REF FRAME: NAD_83(CORS96)(EPOCH: ) ITRF00 (EPOCH: ) LAT: (m) (m) E LON: (m) (m) W LON: (m) (m) EL HGT: (m) 0.005(m) (m) 0.005(m) ORTHO HGT: (m) 0.026(m) [Geoid03 NAVD88] * * 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 63

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. 1st4 H 4/1/12. 2nd4 H 4/1/12. 2last RS 4/1/12. 2last S 4/1/12.1last RS 4/1/12. 1first RS N E h H CORB: PUBLISHED (OLD) "CORB" REFLECTS A PERFECT SCENARIO FOR A CORB: 8 HOURS AS "TRUTH" POINT POSITION SOLUTION D N D E D h NOTES DAY 92 OPUS-S: 1ST 4 THESE ARE NOT INDEPENDENT HOURS OBSERVATIONS OPUS-S: 2ND 4 HOURS THEY SHOW DIFFERENCES WITH SLICING A PIECE OF OPUS-S: 1ST 2 HOURS THE PIE, AND PROCESSING WITH THE TWO PROGRAMS OPUS-RS: 1ST 2 HOURS " OPUS -S: LAST 2 HOURS " OPUS-RS: LAST 2 HOURS " OPUS-RS: 1ST 1 HOUR " OPUS-RS: LAST 1 HOUR " OPUS-RS: 15 MINUTES " SOME OPUS COMPARISONS WITH A PERFECT SITE 64

65 COMPARISON WITH 3/9/12 & 12/1/11 ASHTECH E ANTENNA AT CORB DAY 69 OPUS-S: 9 HOURS THESE ARE NOT INDEPENDENT OBSERVATIONS OPUS-S:MID 2 HOURS THEY SHOW DIFFERENCES WITH SLICING A PIECE OF OPUS-RS: MID 2 HOURS THE PIE, AND PROCESSING WITH THE TWO PROGRAMS OPUS-S: 2 HOURS " OPUS-RS: 2 HOURS " OPUS-RS: 1 HOUR " 2011 DAY 335 OPUS-RS: 15 MINUTES THESE ARE NOT INDEPENDENT OBSERVATIONS OPUS-RS: 1 HOUR THEY SHOW DIFFERENCES WITH SLICING A PIECE OF THE PIE, AND PROCESSING WITH THE TWO PROGRAMS 65

66 66

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 67

68 OPUS PROJECTS: PROJECT SESSION PROCESSING VARYING LEVELS OF ACCESS NETWORK PROCESSING (REQUIRES NGS SANCTIONED TRAINING) 68

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 - DB OBS USED 70% # FIXED AMB 70% OVERALL RMS 3 cm PEAK TO PEAK 4 cm, 8 cm ellipsoid DESCRIPTION PICTURES 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 BLUEBOOKING USING OPUS-S OR OPUS RS WITH REAL TIME POSITIONING FOR SMALL PROJECTS- PERFORMED ORIGINALLY BY NCGS 69

70 70

71 HORIZONAL ERROR ELLIPSE FROM COOVARIANCE ± 1.15 CM ± 1.05 CM 1. INTER STATION DISTANCE FROM SOFTWARE COMPUTATION HORIZONAL ERROR ELLIPSE FROM COOVARIANCE ± 1.15 CM ± 1.05 CM HORIZONAL ERROR ELLIPSE FROM COOVARIANCE ± 1.15 CM ± 1.05 CM 1. INTER STATION DISTANCE & DIRECTION FROM SOFTWARE COMPUTATION HORIZONAL ERROR ELLIPSE FROM COOVARIANCE ± 1.15 CM ± 1.05 CM 2. INTER STATION DISTANCE POSSIBLE TRUE DISTANCE 2. EXAMPLE: SAY DISTANCE 1. = SAY DISTANCE 2. = 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 ±). EXAMPLE: SAY DISTANCE 1. = SAY DISTANCE 2. = ERROR = 1 IN ± 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. 71

72 INTER STATION ELEVATION DIFFERENCE FROM SOFTWARE COMPUTATION VERTICAL 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. RECOMMENDATIONS FOR GNSS POINT PAIRS AS SITE CONTROL SET POINT PAIR AS FAR APART AS POSSIBLE, WITH OPEN SKY EVEN IF A P.O.L. IS NECESSARY FOR THE SITE WORK. HOLD THE STATION WITH THE SUNNIEST SOLUTION STATISTICS AS TRUTH FOR HORIZONTAL. DITTO FOR THE VERTICAL (MAY NOT BE THE SAME POINT). 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. 72

73 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 INTERNET DATA VIA CELL TECHNOLOGY SOFTWARE/FIRMWARE ALGORITHMS GNSS HARDWARE SATELLITE CONSTELLATIONS SATELLITE CODES/FREQUENCIES - 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! 73

74 THE THREE BASE STATION OPTIONS FOR RT REAL TIME GNSS GUIDELINES 1.pdf f 74

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 75

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 76

77 θ MULTIPATH θ = EXTRA DISTANCE 77

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 RTK VS. RTN Cell technology 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 Plus: Easy alignment to the NSRS No ppm (1 ST ORDER) ERROR Extended range Homogeneous Data Easy datum updates RTN -Half the equipment or double the production -No monument reconnaissance/ recovery - No set/break down time -No base baby sitting 78

79 USERS CONCERNS WITH RTN 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? 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. 79

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. 80

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! 81

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? B 4 H & V, KNOWN & TRUSTED POINTS? B LOCALIZATION RESIDUALS-OUTLIERS? FYI: GNSS B DO ANY CAN PASSIVE PROVIDE MARKS GOOD NEED RELATIVE TO BE POSITIONS HELD? IN A PROJECT WHILE STILL NOT CHECKING RT BASE WITHIN TO KNOWNS CALIBRATION IN AN (QUALITY ABSOLUTE TIE TO SENSE NEAREST CALIBRATION POINT)? B SAME OFFICE & FIELD CALIBRATION USED? 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 82

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. 83

84 B CHECK KNOWN BEFORE, DURING, AFTER SESSION. COMPARE POSITIONS WITH/WITHOUT GLONASS. B NECESSARY REDUNDANCY? (U. of CAN T Newcastle) INITIALIZE? BAD CHECKS? PLENTY OF SATS? TRY: B WHAT ACCURACY IS NEEDED? TURN OFF GLONASS IF YOU HAVE 6 RT REMEMBER PPM COMMON GPS SATS RT BASE PRECISION TO NEAREST REININTIALIZE CALIBRATION POINT CHECK FOR NOISY SATS IN DATA B AVERAGE REDUNDANT SHOTS COLLECTOR PRECISION DIFFERENCE WITHIN NEEDS OF LOOK SURVEY FOR MULTIPATH NEARBY ALSO-COMPARE B BE AWARE GNSS OF POTENTIAL POSITION INTERFERENCE TO GPS ONLY (E.G., POSITION HIGH TENSION TOWER LINES) Comparison of 30 Minute Solutions - Precise Orbit; Hopfield (0); IONOFREE (30 Minute solutions computed on the hour and the half hour) MOLA to RV Km Day 264 dh (m) Hours Diff. Day 265 THE IMPORTANCE OF REDUNDANCY dh (m) Day 264 * minus diff Day 265 >2 (cm) cm Mean dh (m) Mean dh minus "Truth" (cm) 14:00-14: hrs 17:00-17: :30-15: hrs 17:30-18: :00-15: hrs 18:00-18: :30-16: hrs 18:30-19: :00-16: hrs 19:00-19: :30-17: hrs 19:30-20: :00-17: hrs 20:00-20: :30-18: hrs 20:30-21: :00-18: hrs 15:00-15: :30-19: hrs 15:30-16: :00-19: hrs 16:00-16: :30-20: hrs 16:30-17: :00-20: hrs 14:00-14: :30-21: hrs 14:30-15: * "Truth" 14:00-21: :00-21: * diff >2 cm Two Days/Same Time > Difference = 0.3 cm Truth = Difference = 2.3 cm Two Days/ Different Times > Difference = 4.1 cm Truth = Difference = 0.1 cm 84

85 FURTHER WORK IN THE OFFICE VECTOR & EQUIPMENT REVIEW 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 85

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 86

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 87