network rtk and rtk networks: getting the best out of...

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