1<br />Extract buildings from AHN2 data<br />Xander Bakker<br />Grontmij<br />Team GIS<br />
2<br />Some background information<br /><ul><li>Client calculates the locations for their communication network
A ‘Clutter’ holds base data on surface including object heights classification
Grontmij has provided the clutter dataset in 2004
Some updates on object heights were done in 2005</li></li></ul><li>3<br />Some background information<br /><ul><li>Client ...
Previous updates were based on AHN1 (5m Min and Max grids)
AHN1 is outdated, AHN2 is available for large parts of interest area.</li></li></ul><li>4<br />LiDAR <br />(Light Detectio...
Return time defines surface height
Multiple returns possible
AHN2: 30 points per m²
AHN2: precision is approx. 5 cm</li></li></ul><li>5<br />LiDAR 3D point clouds <br />
6<br />AHN2 products<br />Pricing / km² <br />(< 1.250 km²)<br />€ 56,-<br />€ 56,-<br />€ 28,-<br />€ 28,-<br />€ 28,-<br...
7<br />LASER points<br />Unfiltered points<br />Filtered points<br />Point cloud<br />TIN<br />
8<br />Filtered grid 0.5 m/pix (Bare Earth)<br />Not Interpolated<br />Interpolated<br />
9<br />Unfiltered grid 0.5m/pix<br />The only raster  AHN2  product  that holds information on objects…<br />
10<br />Profile unfiltered grid 0.5m/pix<br />ditch<br />river<br />tree<br />road<br />hedge<br />farm<br />
11<br />LIDAR Analyst v4.2<br />
12<br />LIDAR Analyst v4.2<br /><ul><li>Vector output (3D)
Attributed data
Extraction of buildings, trees and forest
Enhancement tools
Batch processing
Complex parameters
Parameters vary per area
Long processing time         (estimated 20 minutes CPU per AHN2 subunit)
Manual corrections required
Expensive extension (>10K US$)</li></li></ul><li>13<br />ArcGIS 9.4 and AHN2<br />10<br />ArcGIS 9.3<br />ArcGIS 9.4 10<br...
14<br />ArcGIS 9.3 Spatial Analyst / ArcObjects<br />Simple Case : Buildings exist in TOP10<br />TOP10 buildings<br />Regi...
15<br />Common Exceptions<br /><ul><li>Buildings not in TOP10
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Detecting Buildings in AHN2 LiDAR data with ArcGIS - Grontmij

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This presentation shows how AHN2 LiDAR data was used to depict buildings and determine object heights

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Transcript of "Detecting Buildings in AHN2 LiDAR data with ArcGIS - Grontmij"

  1. 1. 1<br />Extract buildings from AHN2 data<br />Xander Bakker<br />Grontmij<br />Team GIS<br />
  2. 2. 2<br />Some background information<br /><ul><li>Client calculates the locations for their communication network
  3. 3. A ‘Clutter’ holds base data on surface including object heights classification
  4. 4. Grontmij has provided the clutter dataset in 2004
  5. 5. Some updates on object heights were done in 2005</li></li></ul><li>3<br />Some background information<br /><ul><li>Client requested us to do an update of the object heights for urban areas currently classified as rural
  6. 6. Using various datasets; NKNL (plans for urban expansion), W&B (population data), aerial photography (Bing) urban expansion areas were identified
  7. 7. Previous updates were based on AHN1 (5m Min and Max grids)
  8. 8. AHN1 is outdated, AHN2 is available for large parts of interest area.</li></li></ul><li>4<br />LiDAR <br />(Light Detection And Ranging)<br /><ul><li>Laser beam is sent to the earth surface
  9. 9. Return time defines surface height
  10. 10. Multiple returns possible
  11. 11. AHN2: 30 points per m²
  12. 12. AHN2: precision is approx. 5 cm</li></li></ul><li>5<br />LiDAR 3D point clouds <br />
  13. 13. 6<br />AHN2 products<br />Pricing / km² <br />(< 1.250 km²)<br />€ 56,-<br />€ 56,-<br />€ 28,-<br />€ 28,-<br />€ 28,-<br />€ 12,-<br />Pricing / km² <br />(<= 15.000 km²)<br />€ 28,-<br />€ 28,-<br />€ 14,-<br />€ 14,-<br />€ 14,-<br />€ 6,-<br />Pricing / NL <br />(> 15.000 km²)<br />€ 455.000,-<br />€ 455.000,-<br />€ 227.500,-<br />€ 227.500,-<br />€ 227.500,-<br />€ 97.500,-<br />Data contains<br />Bare Earth<br />Bare Earth + Objects<br />Bare Earth<br />Bare Earth<br />Bare Earth + Objects<br />Bare Earth<br />Product<br />Filtered laserpoints<br />Unfiltered laserpoints<br />0.5m grid filtered<br />0.5m grid filtered + interpolated<br />0.5m grid unfiltered<br />5m grid filtered<br />The purpose of AHN2 is to get a highly detailed representation of the bare earth (maaiveld). Objects (houses, trees, etc.) are filtered.<br />
  14. 14. 7<br />LASER points<br />Unfiltered points<br />Filtered points<br />Point cloud<br />TIN<br />
  15. 15. 8<br />Filtered grid 0.5 m/pix (Bare Earth)<br />Not Interpolated<br />Interpolated<br />
  16. 16. 9<br />Unfiltered grid 0.5m/pix<br />The only raster AHN2 product that holds information on objects…<br />
  17. 17. 10<br />Profile unfiltered grid 0.5m/pix<br />ditch<br />river<br />tree<br />road<br />hedge<br />farm<br />
  18. 18. 11<br />LIDAR Analyst v4.2<br />
  19. 19. 12<br />LIDAR Analyst v4.2<br /><ul><li>Vector output (3D)
  20. 20. Attributed data
  21. 21. Extraction of buildings, trees and forest
  22. 22. Enhancement tools
  23. 23. Batch processing
  24. 24. Complex parameters
  25. 25. Parameters vary per area
  26. 26. Long processing time (estimated 20 minutes CPU per AHN2 subunit)
  27. 27. Manual corrections required
  28. 28. Expensive extension (>10K US$)</li></li></ul><li>13<br />ArcGIS 9.4 and AHN2<br />10<br />ArcGIS 9.3<br />ArcGIS 9.4 10<br />SOMA (Single Output Map Algebra) will be implemented in ArcGIS 10…<br />
  29. 29. 14<br />ArcGIS 9.3 Spatial Analyst / ArcObjects<br />Simple Case : Buildings exist in TOP10<br />TOP10 buildings<br />Region group<br />Zonal max<br />Zonal max – Focal min<br />AHN2 raster<br />Focal min<br />
  30. 30. 15<br />Common Exceptions<br /><ul><li>Buildings not in TOP10
  31. 31. Buildings contain mainly NoData
  32. 32. Buildings contain extreme low values (sometimes lower than 20m below bare earth)</li></li></ul><li>16<br />Detect Buildings in LiDAR data<br />Liturature suggests ‘Thresholding’<br /><ul><li>Height
  33. 33. Size
  34. 34. Gradient
  35. 35. Slope</li></li></ul><li>17<br />Recent investigation other organizations<br />Object detection <br />using LiDAR and Satellite Imagery<br /><ul><li>Min/Max
  36. 36. NDVI</li></ul>Only works for small areas!<br />
  37. 37. 18<br />Correct AHN<br /><ul><li>Correction of extreme values</li></ul>AHN2 (DSM)<br />SetNull DSM < BE-1<br />Bare Earth (BE)<br />FocalMean on NoData in DSM<br />
  38. 38. 19<br />The object detection process (1)<br /><ul><li>Threshold slope and height</li></ul>Slope < 55°<br />Slope<br />DSM<br />OH > 3m<br />Bare Earth (BE)<br />Object heights<br />Objects (1)<br />
  39. 39. 20<br />The object detection process (2)<br /><ul><li>Include objects from NoData areas</li></ul>Region Group (ND3)<br />Expand (ND2)<br />NoData areas (ND1)<br />DSM<br />Water (WA0)<br />Zonal Sum Water in NoData (WA1)<br />
  40. 40. 21<br />The object detection process (3)<br /><ul><li>Include objects from NoData areas</li></ul>Threshold height<br />Water in NoData (WA1)<br />SetNull (WA2)<br />Zonal Mean (ND4)<br />DSM<br />Final Objects<br />Objects previous steps<br />
  41. 41. 22<br />Calculate object heights<br />
  42. 42. 23<br />Results<br /><ul><li>Buildings not in TOP10 are detected
  43. 43. Buildings mainly covered with NoData are depicted as well</li></ul>1<br />before<br />2<br />3<br />1<br />after<br />2<br />3<br />
  44. 44. 24<br />Results<br /><ul><li>Programmed in ArcObjects
  45. 45. Processing time for 1 subunit is 3 min.
  46. 46. Batchprocessing
  47. 47. Good alternative for lacking data in TOP10
  48. 48. Highways need to be filtered out
  49. 49. Some buildings not detected
  50. 50. Sometimes misclassification due to trees or elevated terrain</li></li></ul><li>25<br />Completeness and correctness<br />Completeness: 286 missing buildings<br /><ul><li>278 detected (97%)
  51. 51. 8 not detected (3%)</li></ul>Correctness: 316 buildings classified<br /><ul><li>278 correctly classified (88%)
  52. 52. 38 misclassified (12%)</li></li></ul><li>26<br />Alternative datasets?<br /><ul><li>Address locations and building blocks missing in TOP10 (BRIDGIS)</li></li></ul><li>27<br />Alternative datasets?<br /><ul><li>BAG</li></li></ul><li>28<br />Lessons learned<br /><ul><li>Processing AHN2 is time consuming and requires large amounts of diskspace (4GB input generated 150GB output)
  53. 53. Many exceptions difficult to account for at forehand
  54. 54. AHN2 order process does not indicate percentage of NoData per subunit
  55. 55. AHN2 data has not been thoroughly checked (subunits entirely filled with NoData, wrong resolution, no crd sys)
  56. 56. TOP10NL is missing a lot of buildings (is not up-to-date)
  57. 57. Generalization of resolution is tricky (use block statistics, set resolution, snap to and extent correctly)</li></li></ul><li>29<br />Questions?<br />Xander Bakker<br />Grontmij Nederland BV :: GIS & ICT - Team GIS :: http://www.Grontmij.nl :: +31 30 220 79 11<br />http://software.grontmij.nl<br />

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