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Network RTK and RTK
networks: Getting the best
out of your rover
The future is now!
To get the best from your GPS/GNSS
rover, you must have true Network RTK!
What are we talking about?
Some definitions
Productivity benefits of Network RTK
Current systems
Some definitions
RTK Network ≠ Network RTK
◦ RTK Network = A number of reference stations connected via
the Internet. Not necessarily VRS. No rover operational
advantage over traditional RTK
◦ Network RTK = Large amount of mathematical processing by
quality software required to produce a VRS network solution (or
MAC) and give you highest precision results at your rover and
fastest initializations
In the industry the distinctions are not clear!
Some definitions
RTK Network
Network RTK/VRS
Always clarify what
you are dealing with!
Some definitions
RTK Network = Traditional RTK,
no added value to your survey
(over using radios). Single base
solution. PPMs build up
Network RTK (esp. VRS) = PPM
values associated with rover
surveying are minimized. Rover
gets best possible initialization time
and precision that rover can
produce. Wide area network
solution
Some definitions
VRS◦ VRS = Virtual Reference Station AKA “non-physical or computed reference station
method”, RTCM v3.1 format definition
◦ Does that mean no connection to a physical station? NO! Survey Controller builds vectors from nearest physical base
◦ What does it mean? Modeling of the ionospheric and geometric (sat.orbs & tropo) corrections for your location. All based on your rover position in the network, not your base station location. This is VRS. PPM minimization
Some definitions
VRS
◦ Rover sends in it’s position to initiate communication with network
◦ Network connects you to nearest physical reference station and computes models based on your position in the network using up to 6 reference stations
◦ Rover operates with superior positioning precision. Physical reference station data is enhanced by VRS modeling
◦ “Fat server & thin client” model
Some definitions
VRS
◦ Network uses high speed Internet technology
to bring together reference station data and
operate a VRS
◦ Rover dials in using wireless mobile Internet
technology to access the Network RTK data.
Two way comms are a must
Permanent
Reference
Stations receive
GNSS signals
24/7
GNSS Data is
streamed via
LAN or Internet
links to central
processing
server
Central server
computes
correction
model for the
area
User in the field
makes
connection to
NTRIP server
via wireless
Internet
NTRIP server
provides list of
available data.
User selects
mountpoint
NTRIP Caster
communicates
with GPSNet.
GPSNet provides
custom solution
for users location
Field user
receives real-
time data
corrected for
local
atmospheric
conditions.
Rover operates
with optimized
precision,
efficiency and
quality control.
Some definitions
What else do we get?
◦ Wireless Internet in the field = greater
productivity
Email in jobs immediately
Stay in touch with office via email
Source information
Some definitions
Benefits of VRS
◦ Significantly reduces systematic errors
Atmospherics, SV orbit corrections
◦ Extended operating range with improved
initialization and precision
◦ Increased productivity
Single person surveying, purchase only a rover
◦ Eliminates need to establish reference station
Set-up, power, physical security become non-issues
Some definitions
MAC
Another NETWORK RTK method
◦ MAC = Master Auxiliary Concept
◦ Part of RTCM v3.1 format recently released
◦ Developed by many manufacturers, academics
etc as part of RTCM 10403.1 committee
◦ This method also known as “RTCM3.1Net”
Some definitions
What is MAC?◦ Networked RTK? YES
◦ Optimized PPM reduction based on rover location? NO Modeling is based on nearest reference station, not
rover location.
◦ “Thin server & Fat client” model i.e. rover does the processing work
◦ All network parameters are sent to the rover for it to solve Shifts all network processing to rover
Provides ability to do broadcast style network RTK
Some definitions
Concepts
◦ The RTCM3.1Net Standard
Network sends all available data to rover, and rover
must build the network solution
Some reduction of PPMs for rover
Some definitions
Concepts
◦ RTCM3.1Net Broadcast mode = one
way comms
◦ Requires many overlapping cells be
designed, and user selects cell
◦ Cell has Master and Auxiliary stations
Some definitions
Concepts
◦ RTCM3.1Net Auto-cell mode
◦ Two way communications
◦ Rover provides position
◦ System builds cell based on rover location
VRS v MAC (RTCM3.1Net)
VRS MAC (RTCM3.1Net) comments
Is this Network RTK? Yes Yes
Network<> Rover communications?
Bi-direction
required Uni- or bi-direction
EG: cell, wifi,
microwave,
900MHz
Majority of processing at? Network server Onboard Rover
Comms bandwidth required? Low Much higher
Focus point for modeling? Rover position
Nearest physical
reference
station
Offered in Trimble VRS networks? Standard feature Standard feature
Also standard
feature is
single station
RTK
Support for older/legacy rovers? Yes No
Support for GLONASS? Yes Yes
GPS+GLN=47SVs
@ Apr 08
Support for DGPS/GIS users? Yes Yes
Formats used
NMEA, RTCM,
CMR NMEA, RTCM
Data and communications optimized
method for PPM reduction? Yes No
Some definitions
Station spacing?
◦ 50-70km for quality network RTK (VRS)
solution?
◦ Can we go further? Only if you’re doing single
station RTK
Why 50-70km?
Some definitions
Why 50-70km?
◦ Troposphere and Ionosphere affect signals
Some definitions
Why 50-70km?
◦ Solar cycle is heading for predicted record
high
Some definitions
Why 50-70km?
◦ Global iono will be active, affecting GPS
Vertical Total Electron Content on a global map, as derived from GPS base
station observations
Some definitions
NTRIP
◦ Networked Transport of RTCM via IP
protocol
◦ Industry standard, manufacturer independent
◦ Developed by BKG: German government
body for cartography and geodesy
A global leader in Geodesy and GeoSciences
Some definitions
NTRIP
◦ A way to send GNSS/GPS observables from
base to rover via the Internet. Both wireless
and traditional Internet technology is used
◦ RTCM or CMR/CMR+/CMRx, you decide.
Some definitions
Why bring up NTRIP?
◦ Supports authentication
◦ Usage and billing
◦ Reduces cost
KYCORS
KYCORS Baselines
TNCORS
TNCORS Baselines
What VRS Can Provide
Put everyone on a common reference frame
Do jobs in half the time, eliminate base activities
Survey with maximum quality precision and initialization times
Using active GNSS control networks
VRS & Other Applications
Not limited to survey applications!
◦ Mapping
◦ Construction
◦ Asset tracking
◦ Any rover that supports RTCM/CMR input
for DGPS or carrier phase processing
Many opportunities
Thanks for listening
Appendixes:
◦ A Real World Project
A Real-World ProjectA test of four methods. Which would you like to use
in your area?
Project Location
Method Park, Wake Co. Raleigh
NC
Deliverables
Horizontal Control
Vertical Control
Site Topography
Plan For The Project
Visit the site to check conditions and set
site control
Survey Site Control
Use site control to do RTK topography
where possible
Use site control to do topography with
reflectorless instrument where RTK is
impossible
Plan
Develop a list of possible existing control
Field reconnaissance for existing control
Do static survey and data processing
Do a site calibration
Do OPUS solution to at least one point.
Do VRS solutions for project control
Do GPS RTK topography
Goal
Figure out which method will allow YOU to
get the job done under budget & ahead of
schedule.
Develop a list of Possible
Control
Get Existing Horizontal & Vertical Control from
NCGS Web Site
http://www.ncgs.state.nc.us/
Go To The Map Index Page
http://www.ncgs.state.nc.us/digitalmaps.html
Identify Possible Project Control
Control:
WADE
OAK
STATE COLLEGE
JAGUARS
ROYS
PULLEN
Recover Known Control
Navigate To Existing Control
Method 1
Plan fast static survey
Develop A Static Network
0
1
3
4
2
Perform Field Observations
Data processing
Network adjustment
&
Publish results for site control
Fast Static
Completed GPS Observation Logs
Samples 3 of 20
Adjusted Grid Coordinates
Errors are reported using 1.96s.
0.029sft465.307sft0.021sft2090799.039sft0.021sft743285.963sft1002
0.028sft461.054sft0.015sft2090393.341sft0.015sft743660.684sft1000
N E e 0.000sft394.973sft0.000sft2086362.315sft0.000sft734303.366sftJAGUARS
e 0.000sft314.845sft0.019sft2099765.993sft0.019sft738465.227sftPULLEN
e 0.000sft419.897sft0.024sft2090741.175sft0.024sft747766.605sftWADE
0.028sft460.806sft0.016sft2090441.409sft0.016sft743289.846sft1001
N E e 0.000sft437.299sft0.000sft2093839.024sft0.000sft740585.831sftSTATE COLLEGE
Fixe errorElevationE errorEastingN errorNorthingPoint Name
Fast Static Survey Network Results
Method 2
Perform field calibration to existing
control
Site Calibration To Station WADE
Field Calibration Map
Field Calibration
Method 3
Perform GPS Observations &
Transmit To NGS For OPUS
Solution
OPUS Solution For Point 1001
Method 4
Obtain VRS Solutions For
Project Control
Using A Cell Phone With A Bluetooth Connection To
Connect To The VRS Network
What If We Had Used
Conventional Control?Traverse Line Lengths:
Line #1-560’ Line #12-333’
Line #2-475’ Line #13-500’
Line #3-660’ Line #14-1000’
Line #4-760’ Line #15-740’
Line #5-686’ Line #16-700’
Line #6-517’ Line #17-616’
Line #7-632’ Line #18-678’
Line #8-494’ Line #19-710’
Line #9-714’ Line #20-707’
Line #10-510’ Line #21-775’
Line #11-376’ Line #22-837’
Total Length: 13,980’ = 2.65 Miles
Finish the deliverables with a
Complete Topographic Survey
For Site
Using GPS Where Open
Using Conventional Survey Methods Where Not
Open
Project ConclusionsAfter doing the project 4 times!
Plus Hypothetical Conventional
Time Comparisons For Control
Establishment Reconnaissance for existing control3 hours
Set Site Control3 People 2 People 1 Person 1 PersonStatic Site RTK Site 1 OPUS Pt VRSControl Calibration Solution Solution6 hours 2.5 hours 2.25 hours .75 hours
Topo Site 2 People4 hours
Allow time for learning to be
successful
Networks of CORS are growing rapidly.
Be aware of the infrastructure growth in
your area.
Single Station>VRS explainedLooking at the differences between singles station
RTK and the two network formats, MAC and VRS.
Survey Background
Services Real Time Kinematic (RTK)
Post Processing Surveying
Surveying with GNSS
Survey receivers use carrier phase processing to compute relative positioning for cm level results in real-time
◦ Single station concept was basis for surveying with GNSS
◦ Multistation and RTCM3.1Net offer improvements
◦ VRS is the ultimate means to survey with GNSS
Surveying with GNSS
Concepts
◦ Single station
Base and Rover required
PPMs increase with distance
Advantageous for legacy rovers and GIS use of RTK
Network
Surveying with GNSS
Concepts
◦ Multistation
Base station is automatically assigned based on your
location
Makes use of the RTK Network concept
No modeling or interpolation
Simplifies field procedures for single base
Surveying with GNSS
Concepts
◦ The RTCM3.1Net Standard
Based on Master Auxiliary Concept (MAC).
Very modern rovers (smart rover) required for
processing the data
Great but limits compatibility with network for legacy
rovers, GIS and other market rovers.
Surveying with GNSS
Concepts
◦ The RTCM3.1Net Standard
Network sends all available data to rover, and rover
must decipher and build solution
Some reduction of PPMs for rover
Surveying with GNSS
Concepts
◦ RTCM3.1Net Broadcast mode
◦ Broadcast = one way comms
◦ Requires many overlapping cells be
designed, and user selects cell
Surveying with GNSS
Concepts
◦ RTCM3.1Net Auto-cell mode
◦ Two way communications
◦ Rover provides position
◦ System builds cell and data
Surveying with GNSS
Concepts
◦ VRS
◦ Also an RTCM 3.1 standard known as “Non-
physical base” method
Surveying with GNSS
VRS modeling
◦ Iono single layer modeling
◦ Tropo model (Modified Hopfield)
◦ SV orbit corrections
◦ Reference station multipath
Surveying with GNSS
VRS modeling
◦ All based on rover position
◦ Processing workload at server, not rover
VRS established
Surveying with GNSS
VRS modeling
◦ Optimized reduction of PPMs
◦ Master station and 6 others contribute to
modeling
VRS established
