AHN: The need for a nation wide digital elevation model

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  • 1. AHN: The need for anation wide digitalelevation modelNiels van der ZonNovember 14, 2012SPAR Europe 2012, The Hague
  • 2. 20111926Need for spatialdata is evident2003
  • 3. 1. The need for a national elevation model in theNetherlands2. National Dutch elevation model AHN23. Future: AHN3, development and challengesSubjects
  • 4. • The Netherlands is an exampleof a country highly susceptibleto both sea-level rise and riverflooding.• 55% of its territory is below sealevel where 60% of itspopulation lives and 65% of itsGross National Product (GNP) isproduced.The Netherlands“Dry feet, sufficient clean water and reliable and usefulinformation.”
  • 5. Facts and figures:• Flood control, drainage and irrigation, water quality,wastewater treatment• Developing and managing national infrastructure networks• 10 million people and € 2,000.- billion value behind dunesand dikes• 17,500 km dikes / 225,000 km canals and rivers• 3,000 diked marshes• Water system of 35,000 km2; 65,000 km2 incl. North SeaWatermanagement ..
  • 6. To know how the water flows:• through the rivers and canals• after a dike break• after a heavy downpour of rain• below groundWhy is elevation data so important?!
  • 7. .. a water model consists of 80% from an elevation model ..WatermodelSource: Nelen & Schuurmans
  • 8. .. a proper watermodel is a detailed model ..Watermodelthe outside world100m x 100m0.5m x 0.5mSource: Nelen & Schuurmans
  • 9. Benefits from detailed watermodelSource: Nelen & Schuurmans
  • 10. • Rijkswaterstaat and waterauthorities jointly responsiblefor safety of the Netherlands by proper water- andfloodmanagement;• Up-to-date elevation data is indispensable• Guarantee: quality, availability and accessibility• Government: is in charge (directing role)• Business: companies perform work out• Further objectives: cost saving by cooperating andpromote use of data by third partiesWhy government into the lead?!
  • 11. Product:• detailed and accurate elevation model• Not only used for information on elevation,but also used for 3D-mappingAHN: solid basis for the use of height in other nationalgeometric base registrationsAHN: national elevation model
  • 12. Major drivers for AHN2:• Legislation (december 2009: Water Act): every 6 yearsquality and safety check• Information needs: detailed data of barriers besidefloodmanagement• Technology push: lidar technique becomes moremature• Climate change adaption: sea-level raising and severerainfalls• Outdated data: between 2003-2005 no data collection(not by market and not by government)• government takes control: quarantee quality,availability, continuityAHN2 (2008-2012)
  • 13. In theory:• Height accuracy: 5cm stochastic en 5systematic• Mapping accuracy: objects 2x2m max.deviation of 50cm• Filtering: terrain dataset and anotherdataset with all filtered topography• Grid file: 0,5m grid is base productIn practice:• Some degrees of freedom for dataacquisition companies:• Planimetric accuracy (sigma_XY)• Point distribution (regularity)• Point density (# point/m2)Quality of AHN: geometrically verifiable(location and height)!AHN2: the quality
  • 14. • About 400.000.000.000 LIDAR points• Accuracy 5cm• Also available in grids (0.5x0.5m)AHN2: the details
  • 15. • Contractor is responsible to ‘supply evidence’ of the qualitydemanded• QA: done by independent contractor• Small market, limited number of parties (3 different parties)• No direct relation between contractor DA and QA• Methodology developed in collaboration with University ofTwente• More efficient and cheaper than done by government itselfAHN2: Quality AssuranceExecutiveorganizationContractorData AcquisitionContractorQuality Assurance
  • 16. Water authorities and Rijkswaterstaat• Quality and safety check barriers• Drainage maps• Hydrological models• Monitoring of coastal erosion / subsidence• Scheduling of major infrastructural work• Ordinances relating to water levels• Planning buffers between ground waterlevels and location of pumping stationsAHN2: applications
  • 17. • WHY: water authorities need update forwatermanagement (i.e. safety check dikes; Water Act)• WHAT: AHN3 is the new updated and improvedversion of AHN2with additional targets:• Hybrid model: special products (if needed) only bydedicated funding• Business opportunities between companies andgovernment• Funding by participating governmentparties for nationwide elevation model;aim is funding by central governmentNext-generation: AHN3 (2014-2019)basic-product AHN3specialsbusiness
  • 18. 1. Further classification: terrain, building, infastructures+ the rest2. RGB coding and laser intensity value per point3. Echo count for automatic classification (by business)(e.g. vegetation); full wave optional4. Pointclouds in LAZ format.5. Griddata: INSPIRE-proof (RD/NAP and ETRS89/EVRS)6. Shorter leap time (max 6 months) between dataacquisition and supplyAHN3 vs AHN2: the major changes
  • 19. LIDARINSARDENSE matchingMobile Mapping SystemsUAV’sAHN3: based on LIDAR ..
  • 20. Data integration:Keep the AHN up-to-date without the need forLIDAR acquisition on a yearly basis, at anational scaleSatellite images Aerial photogrammetry airborne LIDARMajor challenge AHN3
  • 21. Production of pointclouds based on stereophotography (corresponding points; in theory every pixel1 height value)Accuracy / density depends on quality of images:• orientation parameters, overlap, resolution, radiometry• Central governmental program for aerial photography ofthe Netherlands: 10cm on a yearly basis (since 2012)Dense matchingResolutionOverlap10cm60%/30%10cm80%/30%10cm80%/60%vertical accuracy 1σ = 9.7cm 1σ = 2.9cm 1σ = 2.8cm% mismatch 9% > 29.1cm(3σ)11% > 8.7cm(3σ)8.5% > 8.4cm(3σ)AHN21σ < 5.0cm0,3 % > 15 cm (3σ)
  • 22. • Comparatively cheap .. if images are available• Requires much computation time (hours per model)• Suitable for pointcloud production of smaller areas(neighborhoods, buildings, roads and bridges)Disadvantages:• Height accuracy less than LIDAR• Poor in area with weak colour contrast (terrain,streets)• Occlusion in urban area’s; mismatch (%) is large• (Almost) no points under vegetation/trees• Large overlap (€) needed for accuarcy at LIDAR levelDense matching
  • 23. Niels van der Zonn.vanderzon@hetwaterschapshuis.nlAHN: The need for anation wide digitalelevation model