Best RTN RTK Practices OGUG 11 Jan 2012 Bays

Best Practices for using a Real-time GPS Network

Ken Bays, PLS Lead Geodetic Surveyor

Oregon Department of Transportation

BB

Best GPS Practices Panel GPS Nuts & Bolts Workshop Oregon GPS Users Group

Albany, OR 11 January 2012

http://www.ogug.net/Presentations/Best_RTN_RTK_Practices_OGUG_11_Jan_2012_Bays.pdf

Overview Advantages of Using a Real-time GPS Network What you should know about your RTN Best Practices for Using an RTN Other information sources on RTK best practices


Advantages of Using a Real-time Network

Less equipment to purchase Less time searching for passive marks No base set-up time Less crew time GPS baby sitting Stable base stations Automatic tie to the NSRS & a defined coordinate system Better accuracy than single base RTK


Advantages of Using a Real-time Network Operator sets up on wrong station Wrong coordinates for base are entered into data recorder Wrong height of antenna measurement Wrong antenna type picked Antenna not plumb over point Subject to tripod movement or disturbance (wind, bumped, etc.) • Subject to interference with GPS signal (trucks

passing, etc.)


Single Baseline RTK Solution

Single base RTK Accuracy = 10mm + 1ppm 30km: 10mm + 30mm = 40mm


Network RTK Solution

A “Network” RTK corrector is based on several base stations


Network RTK Solution

Distance Dependent Errors can be modeled with reasonable success, almost negating the ppm component. 30km: may achieve near 10mm accuracy


Comparison of Ephemerides Broadcast (predicted) Ephemeris • Sent from GPS satellites as part of the

navigation message when you are collecting data.

Precises Emphemerides • Ultra-rapid Ephemeris

ORGN Spider software grabs then predicted half of the Ultra Rapid Emphemeris every six hours and applies to RT correctors transmitted by the ORGN.

• Rapid Ephemeris • Final Precise Ephemeris


Precise Orbits: prior to late 2009


Know Your Real-time GPS Network

How are positions of the RTN CORS sites computed? • What datum realization? • Is it tied to the NSRS?

What percent of the RTN’s stations are NGS CORS stations? Site installations • Pre-installation QC Data Sets performed? • Antenna Mount Stability? • Sky Visibility? • Photos available? • Site Logs Current?


Know Your Real-time GPS Network

Monitoring & support Costs to use the RTN What constellations used by the RTN? Can any brand of rover be used? • RTCM format correctors

What antenna calibration type used by RTN software? What types of products are available • Post processing • RT Correctors

Single base Network (multi-base)


Best Practices for Using an RTN Check out the RTN you intend to use Check cell coverage in project area • Visit the site • Vendor data coverage maps are unreliable Planning • Mission planning software • Check NANU’s • Check space weather: 2013 Max • Check RTN operational status Consider and test OCRS zone for project • OCRS web tool


Best Practices for Using an RTN Check equipment before and after job • Tribrachs, level bubbles, rod tips, antenna adapters

If not fixed height rod or tripod, measure HI in ft and meters Check rover configuration • Send GGA • NTRIP user ID and password • Set reference station sensor as: unknown • Set reference antenna to: Null or ARP (NGS diagram ARP vs PC)

Check into fiducial points on project Observe redundant measurements • Independent occupations • NGS: “RT positioning of important data points cannot be done reliably

without some form of redundancy. “ NGS User Guidelines for Real Time GNSS Positioning

Perform site calibration/localization as needed to match passive control


NGS single base guidelines

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


NGS Guidelines for RTNs

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


Getting Started w ORGN

ftp://ftp.odot.state.or.us/ORGN/Documents/Getting%20Started%20With%20The%20ORGN.pdf


2012 OSU Survey Workshops http://cce.oregonstate.edu/workshops/surveying/workshops.html

Basic GPS • Thursday, February 2 • Mark Armstrong, NGS OR Advisor &

Michael Olsen, Professor of Geomatics Oregon Real-time GPS Network • Friday, February 4 • ODOT Geometronics Staff


Contact ORGN

www.TheORGN.net E-mail: [email protected] Ron Singh, PLS 503-986-3033 Business Manager

Ken Bays, PLS 503-986-3543 Technical Manager

Randy Oberg, PLS 503-986-3041 Ops & Tech Support



Oregon Coordinate Reference System


Frequently seen problems

Area Data Outages No GGA stream sent Station Outages (try to keep alerts current)

Too Many Concurrent users Rover Configuration Errors We do/will go out on the ground and work with users
