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The Iowa Real
Time Network
(IaRTN)
Steve Milligan, PLS
Statewide RTN Coordinator
Iowa Dept. of Transportation
Shallow Exploration Drillers Clinic
2014
April 9, 2014
• What is a real time network
• Single base RTK versus network RTK
• How network RTK works
• The Iowa Real Time Network (IaRTN)
- Components
- Design considerations
- Expectations
- Base station layout
• Using the IaRTN
• The Iowa Regional Coordinate System
• IaRTN Registration Process
• A network of GPS
base stations operating
in real time
• Can be used for more
than one application
– surveying/engineering
– construction
– agriculture
– structure monitoring
– navigation
– GIS
What Is A Real Time Network?
• Minimizes single base line errors - Models out the atmospheric errors to give you better accuracy, and allows you
to work significantly farther from a base
Single Base RTK vs Network RTK
Advantages of Network RTK
Single Base RTK vs Network RTK
Single Base RTK GPS
Single Base RTK vs Network RTK
Network RTK GPS
• Not tied to a single base station - Designed to allow use with the closest base station down and still get the
desirable accuracy/precision
• More productivity & cost savings - Eliminates setting up a base station
- Spend less time looking for control
- Only ½ of the GPS equipment is needed to do the work or twice the work can
be done with same amount of GPS equipment
Single Base RTK vs Network RTK
Advantages of Network RTK
• A Cellular Based Network - Relies on the private sector cellular providers
- Requires reliable cellular data service
- Cellular data coverage is not equal across Iowa
- A monthly cellular service cost
• Additional Communication Networks Required - Dependent on private & public communication networks
- No control over outside communication problems
Single Base RTK vs Network RTK
Disadvantages of Network RTK
Base stations - Collect GPS info from the satellites & send the info to the Central Server
Central Server - Processes the data & sends the GPS corrections to the internet for the end-
users
End-users - Access the internet for post processing or to use RTK
How Does Network RTK GPS Work?
Base Stations
• Continually operating
reference stations (CORS)
• Collect the GPS data
• Consist of 3 parts
- GPS Antenna
- GPS Receiver
- Network Connection
How Does Network RTK GPS Work?
GPS Antenna
Leica geodetic antenna on a 3” spun aluminum mast
Iowa Real Time Network (IaRTN)
Building Mounts
Iowa Real Time Network (IaRTN)
Ground Mount (1 in IaRTN)
Iowa Real Time Network (IaRTN)
• concrete structure:
8’ to 12’ below grade & 5’ to 6 ‘above grade
• aluminum mast: 8’ to 16’ tall
Disadvantages:
• height of GPS antenna
building mounts - 36’ typical
ground mount - 22’ maximum
• additional costs - ± $20,000 per site
concrete structure
aluminum mast
receiver enclosure
electric to mount
communications
GPS Receiver Leica GNSS receiver
Iowa Real Time Network (IaRTN)
(Located in IT/Communications area of maintenance building)
Communications network equipment
Base Station Network Connection
Iowa Real Time Network (IaRTN)
Data Processing
Iowa Real Time Network (IaRTN)
• RTK Solutions Leica Geosystem’s SpiderNet processing
software provides both single baseline
& network RTK solutions
• Post Processing - Hourly RINEX files are posted on the
IaRTN ftp site
- Leica Geosystem’s SpiderWeb provides
access multiple hour RINEX files
End Users
Iowa Real Time Network (IaRTN)
• Access is through the
internet for both RTK & post
processing
• An internet based RTK
network
• Firewall between IDOT
servers and the internet
access
• 75 km base lines (maximum)
• Stable structures for GPS antennas
- No wood or metal buildings
• Clear sky view
• Use of the IDOT’s existing communications network
- most critical consideration
• Designed to the Nation Geodectic Survey’s (NGS) Continually
Operating Reference Station standards
- 24 IaRTN sites are also NGS CORS sites
IaRTN Design Considerations
• Accuracy & Precision - Horizontal – 1 cm
- Vertical – 2 cm
• Provide Statewide Coverage - With IDOT GPS base stations
- Supplement border areas with other states base stations
• Open Architecture - Make network usable by any current vender’s GPS equipment
- Ability to incorporate any GPS vender’s base stations into the network
IaRTN Expectations
82 base stations providing statewide coverage
IaRTN Base Station Layout
IaRTN Base Station Layout
Augmented by 10 Minnesota, 7 Missouri & 3 Wisconsin DOT GPS base stations
• Using the IaRTN is very easy! - Turn on your GPS rover
- Connect to the internet
- Connect to the IaRTN’s IP address (172.206.203.10 - Port 10000)
- Log-in
- Select RTK mount point
- Check 1 to 2 control points
- Ready to go!
Using the IaRTN
• The IaRTN is on NAD83 (2011) - National Geodetic Survey’s (NGS) current realization of NAD83
• Horizontal calibration/localization - necessary for projects on assumed or project specific coordinates
- not needed for projects on state plane coordinates
• Vertical calibration/localization - necessary for projects on assumed elevations or tied to NGS monumentation
- not needed for project elevations based on OPUS or the IaRTN
Iowa Regional Coordinate System
- Classical measurements (tapes or total stations) match GPS measurements without a scale
factor
- No more horizontal site calibration required using the Iowa Real Time Network
- Iowa DOT will be using on their projects once internal documentation is completed
- A horizontal coordinate system
- A low distortion projection
- Designed by a nationally renown LDP
expert with input from the Iowa DOT,
the Iowa Land Surveyors and the Iowa
County Engineers
- Designed to minimize distortions due
to the horizontal component and
vertical relief (goal ±20 ppm max.
distortion)
- 14 zones with some overlap between
zones
- Register via the IaRTN web site
- Submit application
- Receive username & password within 2 working days
- No cost for account
IaRTN Registration Process
http://www.iowadot.gov/rtn/index.aspx
Thank-you!
Steve Milligan
(515) 290-2831 cell
(515) 239-1982 office
http://www.iowadot.gov/rtn/
Iowa Real Time Network (IaRTN)
