CDOT CORS/OPUS Team P. Fromhertz Colorado State Geodetic Advisor National Geodetic Survey (NGS) January 13, 2011

Gotomeeting Call in number: participant passcode:

Topics CDOT CORS/OPUS Team formed Review Goals/Purpose of Team What is CORS and OPUS Review Articles Examine Pilot data Set Next Steps

Goals Determine if CORS/OPUS can fulfill CDOT needs Update Manual Understand whether CDOT needs more CORS across the State and if so where and at what density.

Topics 1.Use CORS/OPUS to bring in horizontal control to a project area to serve as a starting position instead of tieing into a HARN. 2.Use CORS/OPUS to get coordinates on all your survey control project horizontal coordinates (instead of running RTK). 3.Use CORS/OPUS to establish a vertical starting height for a project area. 4.Use CORS/OPUS on project control vertically.

CORS Annual Benefits

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2010 May 11Federal Geospatial Summit8

time zone date start time # hours select CORS epoch rate coords, met, datasheet, orbits, zip? RINEX: 1 30-second epoch = 125KB User Friendly CORS

OPUSOPUS

Why do we need OPUS? Recognize most positioning done with GPS Want to provide fast, accurate, consistent, reliable access to NSRS CORS data alone does not ensure consistency OPUS –NGS computers –NGS software –Standard parameterization –Standard coordinates/velocities –Your machine talks to our machine

What is OPUS? OPUS is an acronym for: – Online Positioning User Service (OPUS) It started as a service for Static GPS users and has grown from there to serve other users. Designed to work with minimal data input from user and be as fully automated as possible. Only a Web Browser and needed to use. Fast, easy, consistent access to NSRS.

Many Flavors of OPUS Planned OPUS-S (static) » $$$ receiver, hours of data OPUS-RS (rapid static) minutes » $$$ receiver, minutes of data OPUS-DB (database) share results » $$$ receiver, hours of data, share results OPUS-Projects – Beta » Multiple » Multiple $$$ receivers, share results OPUS-GIS – not released ?? » ¢¢ receiver » ¢¢ receiver, minutes of data OPUS-Leveling – LOCUS

OPUS has been popular

L1/L2 GPS data >>> Processed automatically on NGS computers OPUS-S (2-48 hrs): ties to 3 CORS or OPUS-RS (15 min–2 hrs): ties to 9 CORS Solution via - in minutes Fast, easy, consistent access to NSRS Online Positioning User Service (OPUS)

How does OPUS work? Each OPUS ‘flavor’ is a bit different Let’s start with OPUS-S Then, we’ll highlight the differences in – OPUS-RS – OPUS-DB – OPUS-Projects

OPUS-S OPUS-Static, (formerly just called OPUS and sometimes now called OPUS-CLASSIC) Basic Steps – Submit GPS data to OPUS Web site – Processed automatically on NGS computers Ties to 3 CORS stations – Solution via - in minutes – Fast, easy, consistent access to NSRS

How Does OPUS Compute Position? NGS-PAGES software used L3-fixed solution w/ tropo adjusted 3 “best” CORS selected 3 separate baselines computed 3 separate positions averaged Position differences also include any errors in CORS coordinates

How Does OPUS select CORS 1.Estimate remote station position 2.Compute distance to every available CORS 3.Selected CORS assigned 0.0 distance 4.Sort CORS by increasing distance 5.Select the 5 closest CORS 6.Look at 1 st 3 CORS with TEQC program ● covers remote data span ● > 80% data available ● low multipath ● replace with 4 th (then 5 th ) 7.Start single baseline solutions on 1 st 3 CORS ● check solution quality ● if bad solution, replace CORS with 4 th (then 5 th )

OPUS Guidelines address for results Data file with 2 hrs to 48 hrs of GPS L1/L2 data – Static GPS observations only – 30-second epochs processed – not approved for less than 2 hrs of data, but you can try Antenna type/phase model Antenna height from mark-to-ARP vertical

OPUS Website (all flavors)

OPUS Inputs – GPS file -.dat or Rinex (.obs) – you may zip several files together – IF they all have same antenna type and antenna height. – Antennas need not be same serial numbers

Allowable Data Formats RINEX Receiver Independent Exchange—uncompressed Manufacturer’s native / raw (binary) — Uncompressed--as long as UNAVCO’s TEQC program can process it Compressed archive of multiple files. Archive must contain RINEX “site123h.04o” or Hatanaka “site123h.04d” Compressed individual files. “ Site123h.zip”must contain “site123h.06o” or “site123h.06d”

OPUS Inputs – GPS file -.dat or Rinex (.obs) – you may zip several files together – IF they all have same antenna type and antenna height. – Antennas need not be same serial numbers Antenna Type – TRM (choose from list) Antenna Ht – vertical measure from mark to ARP

ARP MARK Antenna Height True vertical distance measured in meters

Why Do I Need the Antenna Type? L1/L2 phase centers are around here Antenna Reference Point (ARP) antenna offsets relate ARP w/ phase centers & are passed to processing software if no antenna type selected, offsets are set to 0 & phase center becomes the reference incorrect or missing antenna type  large vertical errors

Antenna Phase Center Variation SV 14 SV 20 Antenna Type A Antenna Type B Different Phase Patterns SV elevation and varying phase patterns affect signal interpretation differently

OPUS Inputs – GPS file -.dat or Rinex (.obs) – you may zip several files together – IF they all have same antenna type and antenna height. – Antennas need not be same serial numbers Antenna Type – TRM (choose from list) Antenna Ht – vertical measure from mark to ARP Options – Next 3 slides

OPUS Inputs (OPTIONS 1 & 2) specify SPCS specify CORS

OPUS Inputs (OPTIONS 3, 4, & 5) Specify GEOID model: Auto GEOID09 GEOID03 Choose OUTPUT type Choose XML or not

OPUS Inputs (OPTIONS 6, 7, & 8) OPUS-Projects Keyword Set USER Profile Choose PUBLISH and Submit

OPUS Positions NGS PAGES processing software Ionospheric-free solution Tropospheric scale height adjusted Fixed ambiguities Average of 3 unique CORS ties ITRF & NAD83 coordinates/errors + CORS A CORS B CORS C Average

OPUS Report

OPUS Report – check results > 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

How Does OPUS Compute Errors? EW S N 1 σ standard deviation peak-to-peak error more conservative ~ 2 σ peak-to-peak distances

WHAT IS A GOOD SOLUTION? No hard rules - only guidelines Make sure antenna type and antenna height are correct Review statistics should use 90% or more of your observations at least 50% of the ambiguities should be fixed overall RMS should seldom exceed 3.0 cm peak to peak should seldom exceed 5.0 cm

Precise (Final) 14 days latency 1 cm accuracy updated weekly Rapid 1 day latency 2 cm accuracy updated daily UltraRapid 24 hrs observed / 24 hrs predicted 5 cm / 10 cm accuracy updated 4 times/day NGS/IGS PRECISE ORBITS

OPUS Extended Output HTDP-transform CORS ITRF coordinates from published epoch to session midpoint Remote station ITRF solution from each CORS G-files – vector components, standard deviations, & correlations for each vector post-fit RMS & # observations per satellite/vector solution covariance matrix-relates errors in each coordinate to every other coordinate network accuracies - H & V summary of NAD83 derivation SPC feet values, if available for user’s state

Articles Accuracy of OPUS solutions for 1- to 4-h observing sessionsobserving sessions, NGS et. al., 2005 Geodetic Connections – OPUS Rapid State, D. Martin, The American Surveyor, 2007 Geodetic Connections – OPUS Rapid State Accuracy assessment of the National Geodetic Survey’s OPUS-RS utility, NGS et al., 2009 Accuracy assessment of the National Geodetic Survey’s OPUS-RS utility Rover Station Positional Accuracies from OPUS as a Function of Reference Station Spacing and Rover Station Occupation Time, NGS et al, Rover Station Positional Accuracies from OPUS as a Function of Reference Station Spacing and Rover Station Occupation Time 40

R5 Pilot Data 41

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R5 Pilot Data Static Data – S 422 – U 422 – X 423 RTK data, CDOT control – MP – MP – MP – MP – MP

44 How much does it matter if you use the correct antenna? Station X 423LatW LongEllipsoidal HT NGS DataSheet TRM TRM_R8_GNSS Differences DataSheet - TRM E DatasSheet - TRM_R8_GNSS OBS Used# Fixed AMBOverall RMS TRM %89%0.15 TRM_R8_GNSS 98% 0.13 Units all in meters

45 How much does it matter if you use the correct antenna? Station X 423LatW LongEllipsoidal HT NGS DataSheet TRM TRM_R8_GNSS TRM_R8_GNSS Day Differences DataSheet - TRM E DatasSheet - TRM_R8_GNSS DataSheet - TRM_R8_GNSS Day E OBS Used# Fixed AMBOverall RMS TRM %89%0.15 TRM_R8_GNSS 98% 0.13 Day %95%0.12 Units all in meters

46 How much does it matter if you use the correct antenna?or which CORS? Station X 423LatW LongEllipsoidal HT NGS DataSheet TRM TRM_R8_GNSS TRM_R8_GNSS Day TRM_R8_GNSS 3 Different CORS P037, AZCN, CNC1 P037, MC02, P POB5, MYT2, ZAB Differences DataSheet - TRM E DatasSheet - TRM_R8_GNSS DatasSheet - TRM_R8_GNSS Day E TRM_R8_GNSS 3 Different CORS P037, MC02, P E POB5, MYT2, ZAB23E OBS Used# Fixed AMBOverall RMS TRM %89%0.15 TRM_R8_GNSS98% 0.13 Day 10198%95%0.12 TRM_R8_GNSS 3 Different CORS98%92%0.16 P037, MC02, P02898%93%0.16 POB5, MYT2, ZAB298%94%0.17 Units all in meters

Demo 47

OPUS-RS (Rapid Static) 15-minute sessions minimum, 4 hr maximum 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-RS geographical coverage (15 minute session) Don’t use OPUS-RS outside areas Where Insufficient CORS exist.

OPUS-RS geographical coverage (60 minute session) Don’t use OPUS-RS outside areas Where Insufficient CORS exist.

OPUS-RS Output “#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: 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:0.307 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 “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 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:0.307 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 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 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:0.307 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 Station Selection

OPUS-RS Interpolative Dilution of Precision (IDOP) OPUS-RS accuracy is dictated by CORS geometry and distances IDOP = local CORS geometry relative to rover location [min = 1/sqrt(#CORS)] RMSD – CORS distances * Forthcoming paper in “GPS Solutions” – Accuracy Assessment of the NGS’s OPUS-RS Utility By C. Schwarz, R. Snay, & T. Soler

Expected OPUS-RS Standard Error Values in E or N Dimension:

OPUS-RS Usage

Estimated Vertical Standard Errors – f(IDOP & RMSD) 15-Minute OPUS-RS Sessions Estimated Horizontal Standard Errors – divide by 3.6

OPUS - RS FILE: x _60.10o OPUS-RS will not attempt a solution because the submitted data was collected at a location that is more than 50 km outside of the area spanned by the set of CORS sites whose GPS data OPUS-RS would use in processing the submitted data. These CORS sites are: r301 mc10 se01 mc05 gsc1 mc08 p031 mc07 mc02 Your station is 59.5 KM outside the polygon enclosing the reference stations 59

Keys to Processing OPUS data Record Model Number and serial numbers of antenna Use Fixed HT tripods Use original file where you can (*.dat file) Check solution 60

OPUS-DataBase (DB) Datasheet OPUS-DB Uses: GPS on BMs PLSS / GCDB Data archive Data sharing

Next Steps Schedule Monthly Meetings Continue looking at and comparing data Target date to Update manuals 62

Thank You! 63