filtering of laserscanner data part 2cors-tr.iku.edu.tr/konecny/laser_filt_part2.pdf · height...

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University of Hannover Institute for Photogrammetry and GeoInformation

FilteringFiltering of Laserscanner of Laserscanner DataData

Part 2Part 2

Dr. Peter LohmannDr. Peter Lohmann

lohmannlohmann@ipi.uni@ipi.uni--hannoverhannover.de.de

University of Hannover Institute for Photogrammetry and GeoInformation

Raw Raw Laserscanner Laserscanner DataData FilteredFiltered Laserscanner Laserscanner DataData

Morphological Morphological FiltersFilters

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University of Hannover Institute for Photogrammetry and GeoInformation

1 1 2 2

1 2

p h p hHp p+

=+ ( )

1

1

n

i i

n

i

p hH

p=∑

∑

Height Height Interpolation Interpolation using using a a weighted mean weighted mean and an and an sectorial approachsectorial approach

University of Hannover Institute for Photogrammetry and GeoInformation

Height Height Interpolation Interpolation using using a a moving moving planeplane

H aX bY c= + +

1 1 1 1 1 1 1 1 1

0 2 2 1 2 2 2 2 2 3 2 2 2

3 3 3 3 3 3 3 3 3

1 1 11, 1, 1,1 1 1

X Y Z Y X Z X Y ZA X Y A Z Y A X Z A X Y Z

X Y Z Y X Z X Y Z= = = =

31 2

0 0 0

, , AA Aa b cA A A

= = =

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University of Hannover Institute for Photogrammetry and GeoInformation

DTM + Base Map 1:5.000 DTM + Base Map 1:5.000 + outline of filtered data

University of Hannover Institute for Photogrammetry and GeoInformation

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University of Hannover Institute for Photogrammetry and GeoInformation

University of Hannover Institute for Photogrammetry and GeoInformation

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University of Hannover Institute for Photogrammetry and GeoInformation

University of Hannover Institute for Photogrammetry and GeoInformation

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University of Hannover Institute for Photogrammetry and GeoInformation

University of Hannover Institute for Photogrammetry and GeoInformation

Reflectance Reflectance & Elevation Image& Elevation Image

What is this???

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University of Hannover Institute for Photogrammetry and GeoInformation

LaserdiodeAntrieb

AblenkspiegelEmpfänger

Phasen-detektor

Daten-Speicher

ENTFERNUNGS-MEßEINHEIT

STRAHLABLENK-EINHEIT

Bodenluke Kabinen-boden

1m

Flight-direction

Sitzschiene

Distance measuring unit

Beam deflection unit

ScaLARSScaLARS –– ScaScanning nning LLaser aser AAltitudeltitude and and RReflectance eflectance SSensor ensor

(Institute (Institute forfor Navigation, University of Stuttgart)Navigation, University of Stuttgart)

University of Hannover Institute for Photogrammetry and GeoInformation

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University of Hannover Institute for Photogrammetry and GeoInformation

ScaLarsScaLarsUniv. of Stuttgart

Tidal land near Friedrichskoog

(heights)

University of Hannover Institute for Photogrammetry and GeoInformation

ScaLarsScaLarsUniv. of Stuttgart

Tidal land near Friedrichskoog

(reflective

image)

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University of Hannover Institute for Photogrammetry and GeoInformation

Effect of different viewing angle using elliptical scan pattern

Foreward looking scan

Reverse looking scan

University of Hannover Institute for Photogrammetry and GeoInformation

Height image

Reflectance Image

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University of Hannover Institute for Photogrammetry and GeoInformation

Reflectance SpectraReflectance Spectra

0.5 0.6 0.7 0.8 0.9

10

20

30

40

50

60

70

80

90 Grass

Birch

Concrete

Asphalt

Water(turbid)

(clear)Wavelenght [µm]

Reflectance [%]

Typical reflectance spectra (Elachi, 1987; Colwell, 1983; Wolfe & Zissis, 1978; Kraus & Schneider, 1988)

University of Hannover Institute for Photogrammetry and GeoInformation

Ternary Object Mask from Reflectance DataTernary Object Mask from Reflectance Data

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University of Hannover Institute for Photogrammetry and GeoInformation

Example for the elevation texture criterion Example for the elevation texture criterion -- raw textureraw texture and and object mean valuesobject mean values

University of Hannover Institute for Photogrammetry and GeoInformation

Example for the gradient magnitude criterionExample for the gradient magnitude criterion

( )( , ) arctan / 2, / 2 g x y dy dxα =( 1, ) ( 1, ); ( , 1) ( , 1)

dx hx y hx ydy hxy hxy= + − −= + − −

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University of Hannover Institute for Photogrammetry and GeoInformation

Example for the gradient azimuthExample for the gradient azimuth angle angle criterioncriterion

University of Hannover Institute for Photogrammetry and GeoInformation

DetectionDetection of of largelarge flatflat buildings usingbuildings using progressive progressive histogramm analysishistogramm analysis

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University of Hannover Institute for Photogrammetry and GeoInformation

Automatic Automatic Detection Detection of of BreaklinesBreaklines

Data setData set::

East frisean island Juist

ALTM 1020

h= 700m

mean point spacing 1,5m

University of Hannover Institute for Photogrammetry and GeoInformation

Detection Detection of of breaklines breaklines on on dikesdikes::

Best results have been obtained with the ‚LoG-Operator’ within HALCON,which uses the Laplacian-Operator ∆g(x,y) and a selectable smoothing σof the Gauss-function.

Implementation:

The derivates of the LoG are approximated by derivates of the Gauss-function Gσ(x,y)

and

.

This results in a detection of an ideal edge

having a maxima and a minima and a zero

crossing (steepest slope of the edge)

2 2

2 2( , ) ( , )( , ) g x y g x yg x yx y

∂ ∂∆ = +

∂ ∂

2 2

2 21( , ) exp

2 2x yG x yσ πσ σ

+= −

2 2 2 2

4 2 21( , ) 1 exp

2 2 2x y x yG x yσ πσ σ σ

+ +∆ = − −

Advantage:- insensitive to noise

- robust edge detection even at low gradients

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University of Hannover Institute for Photogrammetry and GeoInformation

LoG filtered imageThresholdingSkeletonizing

Bottom lines detected

University of Hannover Institute for Photogrammetry and GeoInformation

Top (upper) edge of dike could not be detected because segmentation via thresholds failed.

Therefore the mean curvature H is determined from the derivates of the Gauss-function:

2 2

2 21( , ) exp

2 2x yG x yσ πσ σ

+= −

2 2

2

2

2 2

2

32 2 2

( , ) ( , )1

( , ) ( , ) ( , )2

( , ) ( , )1

( , ) ( , )1

a b cHdg x y g x yax y

g x y g x y g x ybx y y x

g x y g x ycy x

g x y g x ydx y

− +=

∂ ∂= + ⋅ ∂ ∂

∂ ∂ ∂= ⋅ ⋅

∂ ∂ ∂ ∂

∂ ∂= + ⋅ ∂ ∂

∂ ∂= + + ∂ ∂

Implemented within the

„Derivate_gauss“ operator

of HALCON

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University of Hannover Institute for Photogrammetry and GeoInformation

„derivate_gauss“

ridges

University of Hannover Institute for Photogrammetry and GeoInformation

0

1.000

2.000

3.000

4.000

5.000

6.000

5.949.820.000 5.949.830.000 5.949.840.000 5.949.850.000 5.949.860.000 5.949.870.000 5.949.880.000

Y [ m]

0

1.000

2.000

3.000

4.000

5.000

6.000

5.949.850.000 5.949.875.000 5.949.900.000 5.949.925.00

Y [ m]

0

1.000

2.000

3.000

4.000

5.000

5.949.820.000 5.949.840.000 5.949.860.000 5.949.880.000

Y[ m]

1 2 3

3 2

1

ResultsResults

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University of Hannover Institute for Photogrammetry and GeoInformation

University of Hannover Institute for Photogrammetry and GeoInformation

Extraction Extraction of of breaklines breaklines at at the borders the borders of of drainage channels within the wadden seadrainage channels within the wadden sea

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University of Hannover Institute for Photogrammetry and GeoInformation

600

700

800

900

1.000

1.100

1.200

1.300

1.400

2.564.850.000 2.564.865.000 2.564.880.000 2.564.895.000 2.564.910.000 2.564.925.000

R echt swert [ m]

2 2( , ) ( , )'( , ) g x y g x yG x yx yσ

∂ ∂= ⋅

∂ ∂

Averaging the absolut value of the gradient of the Gauss-function yields:

University of Hannover Institute for Photogrammetry and GeoInformation

Applying an recursive edge detection „Deriche“ filter with bandpass characteristics yields:

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University of Hannover Institute for Photogrammetry and GeoInformation

600

700

800

900

1.000

1.100

1.200

1.300

1.400

2.564.850.000 2.564.865.000 2.564.880.000 2.564.895.000 2.564.910.000 2.564.925.000

Y [ m]

1

2

400

500

600

700

800

900

1.000

1.100

1.200

1.300

1.400

2.564.980.000 2.565.000.000 2.565.020.000 2.565.040.000 2.565.060.000 2.565.080.000 2.565.100.000

X [ m]

21

ResultsResults