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LIDAR Accuracy on Asphalt Road Arttu Soininen Terrasolid Ltd Case story Task: produce an accurate asphalt road surface model Purpose: asphalt is going to be resurfaced machinery is going to be automatically guided by total station positioning Note:

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lidar accuracy on asphalt road

LIDAR Accuracy on Asphalt Road

Arttu Soininen

Terrasolid Ltd

case story
Case story
  • Task:
    • produce an accurate asphalt road surface model
  • Purpose:
    • asphalt is going to be resurfaced
    • machinery is going to be automatically guided by total station positioning
  • Note:
    • we assume that total station network is perfect
    • 481 total station points on asphalt for control
    • surrounding terrain is not important
coordinate setup
Coordinate setup
  • TerraScan uses integer coordinate system
  • Sentimeter steps OK for general terrain mapping
  • Use millimeter or 1/10 of a millimeter for best accuracy work
laser scanning
Laser scanning
  • 15 km of road
  • TopEye measured in October 2003 with a scanner measuring about 7000 points per second
  • Digital camera images with 2 cm resolution
  • Flown in two directions at 100 m altitude
initial laser data accuracy
Initial laser data accuracy
  • IMU / scanner misalignment angles carefully calibrated from data set
    • TerraMatch gives no real HRP improvement
  • Average difference between surfaces from different flightlines 3.689 cm
  • Average difference on asphalt 3.440 cm
dz correction for whole flightlines
Dz correction for whole flightlines
  • TerraMatch gave dz corrections for whole flightlines:
    • -1.7 cm line 1
    • +0.7 cm line 2
    • +0.8 cm line 3
    • +0.4 cm line 4
    • -0.2 cm line 5
  • Average difference between surfaces from different flightlines after correction 3.299 cm, on asphalt 2.997 cm
fluctuating elevation correction
Fluctuating elevation correction
  • Corrects for inaccuracy of trajectory elevations
  • TerraMatch computed elevation difference of each flightline to others at 1 second intervals
  • Each 1 second interval was corrected with the average of 3 consecutive seconds
  • Correction limited to max 2 cm
  • Average difference between surfaces from different flightlines 3.070 cm
find fluctuations
Find Fluctuations
  • Correction will modify laser points of each interval with a unique dz correction
  • User can select:
    • how correction curve is averaged from consecutive intervals
    • what is the maximum correction to apply
cutting edges of scan lines
Cutting edges of scan lines
  • TerraScan cut edges of scan lines where accuracy is not as good as at the center of scan lines
geoid correction
Geoid correction
  • Transform from GRS80 ellipsoid to orthometric height
  • Average elevation difference between LIDAR surface and total station points was computed for each 1 km interval
smoothing of laser surface
Smoothing of laser surface
  • Classify points within 10 cm from ground to ground
  • Smoothen laser surface
  • Std dev asphalt against total station points 2.32 cm
smoothing 10 cm spread
Smoothing 10 cm spread
  • Improves accuracy on hard surfaces
  • Requires interactive work -- draw polygons
  • Raises laser data on hard surfaces:
    • systematic biases on different surfaces closer
  • Example before:
    • laser data 5 cm too high on asphalt
    • laser data 9 cm too high in terrain
  • Example after:
    • laser data 7 cm too high on asphalt
    • laser data 9 cm too high in terrain
breaklines on asphalt
Breaklines on asphalt
  • 2D breaklines drawn on orthophoto were draped to laser point surface
    • smoothenes variations in longitudinal direction
  • Std dev of resulting TIN model:
    • fix points 2.02 cm, min -5.60, max +5.30
summary of steps
Summary of steps
  • Match laser strips internally:
    • HRP misalignment  3.440 cm
    • Dz per flightline  2.997 cm
    • Elevation fluctuations  2.705 cm
  • Cut overlap
  • Classify ground
  • Geoid correction based on local points  2.48 cm
  • Classify 10 cm spread and smoothen  2.32 cm
  • Drape breaklines on laser surface
  • Model breaklines + surrounding terrain  2.02 cm