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Improving the Accuracy of Improving the Accuracy of field data cost-effectivelyfield data cost-effectively
, Trimble Navigation Limited
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AgendaAgenda
• Welcome and Introduction• Accuracy Considerations• Solution considerations• Cost considerations• Summary
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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?
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Which asset is it?
IntroductionIntroduction
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10cm 60cm 3m
1m >5m
How do I find it accurately if its buried?......
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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
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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.
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Accuracy ConsiderationsAccuracy Considerations
Source – Ordnance Survey
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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
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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
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What is relative and absolute position?What is relative and absolute position?
Source – Ordnance Survey
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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
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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
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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
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Real-time Correction ServicesReal-time Correction ServicesSatellite- Based Augmentation
SystemsFree serviceSub-metre accuracy
achievable
Limited
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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)
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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
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Solution ConsiderationsSolution Considerations
Cloud
Custom ReportsHTMLPrint to PDF
COTS orCustom
Data Collection
Asset Inspectioneg. “BYOD” + GNSS + other sensors Data
Engine
Web-GIS/Dashboard
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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
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10cm 60cm 3m
1m >5m
How accurate do you need to be?......
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About UsAbout UsMGISS help organisations choose the right mobile GIS solution by:
•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
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Decisions…DecisionsDecisions…Decisions
MGISS are here to provide:•Independent Consultancy/Advice•Sales, Service, Training and Support•Discovery days/ More Webinars!
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www.mgiss.co.uk │ @[email protected]@mgiss.co.uk
T +44(0)151 329 0820│M +44(0)7841 070286IC1, Liverpool Science Park, 131 Mount
Pleasant, Liverpool, L3 5TF