Michigan GPS CORS and The Rapid OPUS Service

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Michigan GPS CORS and The Rapid OPUS Service

• Presentation by
• Brian Soderman
• Senior Student, FSU

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Origins of Michigan GPS CORS

• Established in Fall 2000 by MDOT
• This system was the answer to the question, how
  to complete the multitude of highway survey
  projects in Michigan with less field employees
• Fall of 2004 the Network, became active,
  providing statewide RTK corrections
• This meant that any surveyor with a GPS receiver
  and a suitable connection could now gain access
  to the network and obtain RTK corrections without
  setting up a local base station.

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Design

• All stations in the MSRN are of the Earlconic
  design , for weather reasons.
• Monuments are 12 feet in the ground, 24" in
  diameter with a re-rod reinforced cage. It
  extends 5 feet out of the ground and is
  surmounted with a spun aluminum pole either 8'
  ,16' ,or 18' in height
• The monument is surmounted with a Leica AT504
  choke ring antenna and weather-resisting dome

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Rigid Design
Leica GRX1200 Pro, UPS, Surge Arrestor Connected
to Internet
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The Michigan Spatial Reference Network

• 85 MSRN Stations

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Monument Composition

• All stations rigorously adhere to a 5 degree site
  clearance and have been positioned in locations
  free of excess multipath
• Once the monument is in the ground and
  connectivity to the server is verified, then 30
  days of data is collected and sent to the NGS for
  processing
• The densification of this network and the
  implementation of its real-time capabilities have
  changed forever how GPS and Surveyors perform
  their tasks in the State of Michigan

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WWW.MDOTCORS.ORG
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What is OPUS?

• Online Positioning User Service
• Free service by NGS for GPS users
• Fast and easy to use
• Requires minimum of 2 hours of data
• Useful for checking

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What it Provides

• Provides location of receiver based on raw GPS
  data
• Geographic Coordinates (Latitude/Longitude)
• State Plane Coordinates
• UTM Coordinates
• ITRF and NAD83 Coordinates
• Ellipsoidal and Orthometric Elevation

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What is OPUS-Rapid Static?

• Same purpose as OPUS provides location solution
  to GPS data sets
• Key Advantage Requires only 15 minutes of data
• Accurate 2 cm horizontal, 4 cm vertical
• Brand New January 31, 2007

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What is OPUS-Rapid Static?

• Uses new solution program Rapid Static GPS
  (RSGPS)
• RSGPS uses both P code and carrier phase (L1
  L2) range observations
• LAMBDA (Least Squares Ambiguity Decorrelation
  Adjustment) algorithm to find ambiguity (N)
• Ambiguity difference in number of wavelengths
  between self-generated receiver phase and
  received GPS phase
• D c ?T ?N where c speed of light, ?T time
  difference and N ambiguity in wavelength (?)

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What is OPUS-Rapid Static?

• - Opus computes solution in reference to 3 CORS
  locations
• - CORS sites selected by increasing distance from
  user's station and site stability. Search will
  stop if distance greater than 200 km.
• - If search fails to locate 3 stations, program
  will refuse to attempt a solution
• - Reference stations can be selected manually

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How to use OPUS-Rapid Static

• Service located at http//www.ngs.noaa.gov/OPUS/
• Click OPUS Rapid Static link
• Required Data
• Email address for solution to be sent to
• The GPS data file in RINEX format
• Antenna Type, e.g. Leica ATX1230
• Antenna Height

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How to use OPUS-Rapid Static

• RINEX standard GPS data set file format
• Receiver Independent Exchange format
• RINEX format converter at http//facility.unavco.
  org/software/teqc/teqc.html
• Or use Leica Geo-office

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OPUS-Rapid Static- User Interface
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Results
Wait 30 min. and NGS will send an email with the
solution report.
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Experimental Results

• OPUS RS results similar to standard OPUS
  results
• Greatest horizontal difference only lt 2 cm
  vertical difference significant for point Miller
• Comparison not entirely valid

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Conclusion

• Michigan CORS is a revolutionary system that
  allows for high accuracy positional measurements
• OPUS Rapid Static provide a free and convenient
  means of calculating GPS locations anywhere with
  one system.
• It also provides easy and fast redundancy in GPS
  static measurements

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Any Questions?