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Laserscanning � aktueller Stand in Forschung und Entwicklung
Karl Kraus
Institute of Photogrammetry and Remote Sensing (I.P.F.), Vienna University of Technology
www.ipf.tuwien.ac.at
� Neues gegenüber dem Vorjahr
� Beispiele vor allem aus dem Pulkauprojekt (NÖ)
� Gebäude und Spezifisches zum Hochgebirge erst am Nachmittag
Karl Kraus Laserscanning - aktueller Stand in Forschung und Entwicklung 2
Geo-Referencing
Observations�heights of the control points
�height differences of parallel plane patches calculated from neighbouring points in adjacent strips
Unknowns�heights for all the tie points
�heights for all the control points
�additional parameters for the compensation of the systematic errors
Improvement of the homogeneity in the overlapping areas by a factor between 2 and 4
=> Extension to 3D (with structure line elements) and modelling the flight path, etc.
Karl Kraus Laserscanning - aktueller Stand in Forschung und Entwicklung 3
Geo-Referencing
�Control Point� = a few tilted planes
Karl Kraus Laserscanning - aktueller Stand in Forschung und Entwicklung 4
Projekt Pulkautal
Differenzmodell der Laserscanner-Streifen 10 und 11
nach der simultanen Höheneinpassung
Karl Kraus Laserscanning - aktueller Stand in Forschung und Entwicklung 5
Derivaton of DTMsRobust Linear Prediction
271 control points:
σ = ±18cm
point distance : ~3.1m
σ = ±29cm
point distance: ~1m
=> point density is the most important parameter
Karl Kraus Laserscanning - aktueller Stand in Forschung und Entwicklung 6
Derivation of DTMs (cont.)Robust linear prediction in a hierarchical approach
a) Creation of a data pyramid (lowest point with its xyz-co-ordinates in a regular grid)
b) DTM generation in the coarse level
c) Coarse DTM with a tolerance band
d) DTM generation in the fine(r) level
Karl Kraus Laserscanning - aktueller Stand in Forschung und Entwicklung 7
Derivation of DTMs (cont.)
Laser scanner data with the gaps after the elimination of theoff-terrain points
Kamptal in NÖ, Department of WaterManagement, Hydrology and Hydraulic EngineeringBOKU - University of Natural Resources and Applied Life Sciences, Vienna)
Quality Overlays� distance between each grid point and the next point of the original data set
� variances in small cells derived from the differences between the elevation of the original points and the elevation of the DTM at the same locations
� the density of the points also in this small cells
� σ in each grid point
Karl Kraus Laserscanning - aktueller Stand in Forschung und Entwicklung 8
Projekt Pulkautal
[Punkte/m2] [Punkte/m2]
Punktdichte der original Laserscanner-Punktwolke
Punktdichte der Bodenpunkte
Karl Kraus Laserscanning - aktueller Stand in Forschung und Entwicklung 9
Projekt Pulkautal (cont.)
Abstandsmodell für die Bodenpunkte
Karl Kraus Laserscanning - aktueller Stand in Forschung und Entwicklung 10
Projekt Pulkautal (cont.)
Mittlere Residuen zwischen Laserpunkten und DGM
ursprüngliche Laserpunkte Bodenpunkte
Karl Kraus Laserscanning - aktueller Stand in Forschung und Entwicklung 11
Projekt Pulkautal (cont.)
Manuelle photogrammetrischeDatenerfassung
Photogrammetrisches DGM
Karl Kraus Laserscanning - aktueller Stand in Forschung und Entwicklung 12
Projekt Pulkautal (cont.)
Laserscanner-DGM Orthophoto
Karl Kraus Laserscanning - aktueller Stand in Forschung und Entwicklung 13
Projekt Pulkautal (cont.)
� Photogrammetrie �Modell-Patches�
� Scanlag in ALS
� Kanten in Photogrammetrie
� Kleinformen in ALS
Karl Kraus Laserscanning - aktueller Stand in Forschung und Entwicklung 14
Accuracy and Geomorphologic Quality of Laser Scanner DTMs
Empirical elevation accuracy of LaserScan DTM
tanα . . . Terrain slopen . . . Average number of points per square meter
[ ]
⋅+±= ασ tan1206n
cmz
For flood risk area the accuracy of the positionof the border of predicted flood is of central interest:
ασσ
tanz
xy =
e.g. σz = +/- 12 cm σxy = +/- 25 m ! (tan α = 5%o)
Karl Kraus Laserscanning - aktueller Stand in Forschung und Entwicklung 15
Accuracy and Geomorphologic Quality of Laser Scanner DTMs (cont.)
Flood risk area (project of the Lower-Austrian Govermental Administration)
Karl Kraus Laserscanning - aktueller Stand in Forschung und Entwicklung 16
Geomorphologic Quality of Laser DTMs� only a point cloud� point density is the important parameterWavelike surfaces with a minimal wave length Lmin
Scanning theorem
∆ ≈ Lmin/3
Derivation of breaklines from the point cloud
minimal crown width Bmin
∆ ≈ Bmin/2
Karl Kraus Laserscanning - aktueller Stand in Forschung und Entwicklung 17
Surface Break Lines
Hybrid DTM consisting of a regular raster with 3D vectors
Karl Kraus Laserscanning - aktueller Stand in Forschung und Entwicklung 18
Surface Break Lines (cont.)
How to get the relevant 2D break lines?
Karl Kraus Laserscanning - aktueller Stand in Forschung und Entwicklung 19
Surface Break Lines (cont.)
Automatic procedure: rain simulationSemiautomatic procedurea. Manual digitization as 3D lines in photogrammetic stereomodels
Almtal
Upper-Austria
Govermental
Administration
BEV: The entire territory of Austria* image scale 1:15 000, 21 cm camera* σz = +/- 45 cm (too bad)* σxy = +/- 25 cm (good enough)
Karl Kraus Laserscanning - aktueller Stand in Forschung und Entwicklung 20
Data Reduction
� The very high density of points is a great advantage for improving the quality
� but there are difficulties in the data management.
Derivation in each grid point of the dense DTM:
� radius R of the curvature
� slope tanα
� allowable distance E in order to keep dZ less than threshold dZmax
Idea of progressive sampling
Karl Kraus Laserscanning - aktueller Stand in Forschung und Entwicklung 21
Data Reduction (cont.)
Small example
Wienerwald
MA 41 der
Stadtverwaltung
Wien
Typical example
� 4 millions of grid points
� user defined threshold dZmax = 25cm
� 1.3 million of the reduced points
� 4.75 minutes on a 2 GHz computer including the output in ASCII
Karl Kraus Laserscanning - aktueller Stand in Forschung und Entwicklung 22
Monitoring Flooding Catastrophes
Monoplotting
Different types of images, geo-referenced by GPS and IMU:
� Digital frame camera
� One-line scanner
� Three-line scanner
� Amateur camera (with oblique axes)
� Microwave sensors (for extreme weather conditions in flooding periods)
Karl Kraus Laserscanning - aktueller Stand in Forschung und Entwicklung 23
Monitoring Flooding Catastrophes (cont.)
Scenario� Actual water level and the 3D border lines of the
flood, corresponding to the time when the images have been taken
� Based on short-term prognoses of precipitation,prediction of the rise in water level
� Increase of the actual water level by the predicted rise ⇒ Surface at the predicted water level
� Intersection of the surface of the predicted water level with the precision DTM
⇒ Areas at immediate risk can be plotted
⇒ Catastrophe management can take important decisions and can inform those affected.
A vision: After taking the images final results within one day
Karl Kraus Laserscanning - aktueller Stand in Forschung und Entwicklung 24
Additional Features Relevant to Hydraulics and Hydrology
Model without structure lines:- grid width: 50 m- 55.000 points
Karl Kraus Laserscanning - aktueller Stand in Forschung und Entwicklung 25
Additional Features Relevant to Hydraulics and Hydrology (cont.)
Hydrological analysis:- drainage
dark-blue: valleylight-blue: watershed
developed by:
Rieger W.
Gajski D.
Molnar L.
Dorninger P.
Karl Kraus Laserscanning - aktueller Stand in Forschung und Entwicklung 26
Additional Features Relevant to Hydraulics and Hydrology (cont.)
Hydrological analysis:- lakes (depressions)- rivers
⇒ structure lines
Karl Kraus Laserscanning - aktueller Stand in Forschung und Entwicklung 27
Valles Marineris on the Mars:-10° x 10° = 593 x 593 km-grid width: 463 m / Pixel
Mars Global Surveyor (NASA)1997 � 2001
MOLA (Mars Orbiter Laser Altimeter)
330 m point distances in profiles
Additional Features Relevant to Hydraulics and Hydrology (cont.)
orthophotoz-coding
Karl Kraus Laserscanning - aktueller Stand in Forschung und Entwicklung 28
Additional Features Relevant to Hydraulics and Hydrology (cont.)
Valles Marineris on the Mars:- 10° x 10° = 593 x 593 km- grid width: 463 m / Pixel
river analysisorthophotoz-coding
Karl Kraus Laserscanning - aktueller Stand in Forschung und Entwicklung 29
Additional Features Relevant to Hydraulics and Hydrology (cont.)
Valles Marineris on the Mars:- 10° x 10° = 593 x 593 km- grid width: 463 m / Pixel
depressionsriver analysisorthophotoz-coding
Karl Kraus Laserscanning - aktueller Stand in Forschung und Entwicklung 30
Additional Features Relevant to Hydraulics and Hydrology (cont.)
Perspective view:
- z-coding
- MOC � orthophoto
- lakes and rivers