Presentation Transcript

1. National LiDAR Survey Projects Around 235 000 sqkm surveyed upto 2013 To survey part or whole country to get an overall height model: Netherlands (third round) Finland (0,7 points/ m2 , in some urban areas 1,4 points/ m2 ) Sweden (ready , around same point density as in Finland) Slovenia Poland (in cities 12 points/ m2 ;country side 4 points/ m2) France Australia USA Taiwan Philippines (330.000 sqkm)
2. Public Data from NLS of Finland Download: https://tiedostopalvelu.maanmittauslaitos.fi/tp/kartta?lang=en
3. Header Information of Datasets
4. To Create 3D-Real Estate DataBase in Finland Started
5. General requirements – point clouds(Example by Swedish Landsurvey) Point density minimum 2 point/m2 Multiple returns from laser pulses Maximum scanning angle +/- 20 degrees Minimum 20% overlap between flight lines Minimum 200 m overlap towards adjacent areas Measurement and use of control and check points, both in elevation and planimetry Standard error 0,2 m in elevation at well defined surfaces Standard error 0,6 m in planimetry Standard error for interpolated points 0,5 m for the elevation model Notice: in LiDAR we are not talking about scale!
6. Check List of Airborne LiDAR Control 1. Co-ordinate transformation Check the co-ordinate transformation from global to local system Use orthos, control points and maps as reference 2. Check data calibration • Point strips from adjacent flight lines overlap >20% • Use blocks, where you have slopes or ridge roof buildings in different directions. • Check the fluctuation of data calibration by colours: load only overlapping points, classify them by ground and display ‘distance’ of TerraScan • TerraMatch MeasureMatch tool gives statistics of differences in elevation between overlapping flightlines – Classify ground (and buildings) per flightline for reliable result • Correct for systematic orientation errors by using TerraMatch (Strip Adjustment)
7. Check List of Airborne LiDAR Control 3. Check coverage and point density 4. XY-location • Display points by intensity and verify with road paintings • Verify points from building to orthos or building footprints • Make profiles and compare Lidar with surveyed points • Evaluate offset between Lidar point cloud and terrain profile by using TerraMatch FindMatch (control points representing terrain profile) • Correct for global XY offset • Correct for fluctuating XY offset
8. Check List of Airborne LiDAR Control 5. Z-level • Output control report • Survey control points in groups on hard surfaces, do not use ordinary control points, which are typically higher than the real ground • Correct for global Z offset • Correct for fluctuating Z offset 6. Check the classification of ground points • Overlapping strips are cut (must be done before ground classification) • Points from ’poor quality’ trajectories (crossing lines) are removed (must be done before ground classification) • Check that extra echoes have been removed from ground points. Classification attributes {only echo, last of many }
9. ?? Data Availabale, ask Ramani Geosystems!
10. ?? Problems with clouds/ Images Notiece: LiDAR surveys do not depend on light and time of the day! You can view Google data but not use actively for example in design LiDAR mapping does not release field surveying. One huge need is to survey underground water and sevage pipes
11. Requirements & Costs Urban areas: Good data: 1,4 pts/m2 Images pixel 20 cm Operation 120 €/ sqkm (Finnish National Land Survey) Dar es Salaam 1500 sqkm ~200.000 € + Mobilisation, Data processing etc. ~300.000 € Better data: Point desity 4...5 pt/m2 => altitude Pixel 10 cm Lower altitude => more flight lines => higher costs
12. Questions? QESTIONS?