Improving the Accuracy of Improving the Accuracy of field data cost-effectivelyfield data cost-effectively

, Trimble Navigation Limited

AgendaAgenda

• Welcome and Introduction• Accuracy Considerations• Solution considerations• Cost considerations• Summary

How often do you find that existing records are not mapped correctly or accurately enough?

IntroductionIntroduction

• Which asset is it?• How can I find it accurately if its buried?• Why is the map wrong?

Which asset is it?

IntroductionIntroduction

10cm 60cm 3m

1m >5m

How do I find it accurately if its buried?......

Why is the map wrong?Why is the map wrong?Historically, Ordnance Survey maps were produced at different scales using different surveying methods resulting in varying degrees of accuracy.

There are four accuracy categories.•1:1250 scale•1:2500 scale resurvey/reformed•1:2500 scale overhaul. Maps originally recompiled from pre-1946 County Series mapping•1:10 000 scale.

Ordnance Survey describes accuracy in two ways.•Absolute or positional accuracy.•Relative accuracy Source – www.gov.uk

Accuracy ConsiderationsAccuracy Considerations

Absolute accuracy – A measure which indicates how closely the coordinates of a point on a map eg. Ordnance Survey, agrees with the true National Grid coordinates of the same point on the ground eg. captured with GNSS. Relative accuracy – Relative accuracy compares the precise distance between features measured in the real world to the distance between the equivalent features in the data.

Accuracy ConsiderationsAccuracy Considerations

Source – Ordnance Survey

Source – www.gov.uk

Absolute accuracy

     

Scale RMSE* 95% confidence level

99% confidence level

1:1250 (urban) <±0.5m <±0.8m <±0.9m1:2500 (rural) (resurvey or reformed)

<±1.1m <±1.9m <±2.4m

1:2500 (rural) <±2.8m <±4.7m <±5.8m1:10 000 (mountain and moorland)

<±4.1m <±7.1m <±8.8m

Source – www.gov.uk

Relative accuracy

       

Scale Relative error 95% confidence limit

99% confidence limit

Maximum measured distance

1:1250 (urban)

<±0.5m <±0.9m <±1.1m 60.0m

1:2500 resurvey or reformed (urban and rural)

<±1.0m <±1.9m <±2.5m 100.0m

1:2500 overhaul (urban and rural)

<±1.8m <±3.6m <±4.7m 200.0m

1:10 000 (mountain and moorland)

<±4.0m <±7.7m <±10.1m 500.0m

What is relative and absolute position?What is relative and absolute position?

Source – Ordnance Survey

Working with Map ErrorsWorking with Map Errors• Always work to a minimum of map accuracy• Network assets are predominantly mapped

• Relatively in urban areas• Absolutely in rural areas• Always need to be correctly shown on

the map• High-accuracy GNSS for new data capture

• Store absolute coordinates and capture method. Important for:• Modelling • Relocation• Quality

Achieving Map AccuracyAchieving Map Accuracy

• Choose the right tool for the job• Ensure Mobile GIS software is fit for

purpose• Use up to date OS transformations

OSTN02/OSGM02• Simple “plug and play” scalable GNSS• Create quality flags in workflow/database• Drive behaviour of field teams to capture

data consistently

Technology ConsiderationsTechnology Considerations

• GNSS (not just GPS)• Capturing GNSS quality flags• If not then manual methods need to be

robust (minimum 2 dimensions) • Integrating other sensors (eg. laser

rangefinder, Cable locator)• Real-time corrections• Post-processing GNSS

Real-time Correction ServicesReal-time Correction ServicesSatellite- Based Augmentation

SystemsFree serviceSub-metre accuracy

achievable

Limited

Real-time Correction ServicesReal-time Correction ServicesNetwork VRS (Trimble, Leica, TopCon)Satellite corrections eg. RTX, AtlasUsually require additional antenna/firmware optionVery accurate GNSS positions, typically 30cm-1cmConvenience, no need to setup an additional base Subscription Costs (monthly to annual PAYG)

Solution ConsiderationsSolution Considerations

BluetooothGPS/GNSS

Tablet/Smartphone + Bluetooth GNSS

SpikeLaser Rangefinder + SmartPhone attachment = Calibrated Photos

Survey Grade GNSSeg. Spectra Precision SP80/SP60

eg. Arrow series

eg Trimble R1

GNSS-enabledeg. DSLR camera orCable locator

Solution ConsiderationsSolution Considerations

Cloud

Custom ReportsHTMLPrint to PDF

COTS orCustom

Data Collection

Asset Inspectioneg. “BYOD” + GNSS + other sensors Data

Engine

Web-GIS/Dashboard

Cost ConsiderationsCost Considerations

£300

£1,000

£2,500

£8,500

£300£500

£750

£1,900

£5,000

£7,000

£0

£1,000

£2,000

£3,000

£4,000

£5,000

£6,000

£7,000

£8,000

£9,000

Consumer Prosumer Mapping Surveying

Cos

t £

Accuracy v Cost

GNSS

Software

All in one

Subscriptions

10cm 60cm 3m

1m >5m

How accurate do you need to be?......

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•understanding your requirements•providing independent advice•considering the most cost-effective approach for you•reducing your risk when building a business case and•supporting throughout the project lifecycle

Decisions…DecisionsDecisions…Decisions

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