S. Laguela - Aerial thermography from low-cost UAV for the generation of thermographic digital...

AERIAL THERMOGRAPHY FROM LOW-COST UAV FOR THE GENERATION OF

THERMOGRAPHIC DIGITAL TERRAIN MODELS

S. Lagüela, L. Díaz-Vilariño, D. Roca, J. Armesto

Applied Geotechnologies Research Group, University of Vigo (Spain)

Corresponding Author: [email protected]

INTRODUCTION DATA ACQUISITION

• EQUIPMENT

DATA ACQUISITION

• FLIGHT

THERMOGRAPHIC DTM GENERATION

• THERMOGRAPHIC MOSAIC


• THERMOGRAPHIC DTM TEXTURIZATION

RESULTS AND DISCUSSION

• LAND USES

CONCLUSIONS

AERIAL THERMOGRAPHY FROM LOW-COST UAV FOR THE GENERATION OF THERMOGRAPHIC DIGITAL TERRAIN MODELS

THERMOGRAPHIC INSPECTIONS IN

BUILDINGS

CLOSE RANGE AERIAL THERMOGRAPHY

THERMOGRAPHIC AERIAL ACQUISITIONS


• EQUIPMENT

DATA ACQUISITION

• FLIGHT






• LAND USES

CONCLUSIONS


OBJECTIVE:

Extension of the accurate thermographic studies performed in three-dimensions for buildings

to medium size areas (neighbourhoods, districts, villages) using a low-cost aerial platform


• EQUIPMENT

DATA ACQUISITION

• FLIGHT






• LAND USES

CONCLUSIONS


Okto XL by Mikrokopter

• 2 kilograms payload

• 20 min flight autonomy

Gobi384 by Xenics with 10mm lens

• 384x288 UFPA

• 50 fps data acquisition

• 500 grams (lens included)

> NO LIMITS TO COPTER SPEED

> NOT EXCEEDING COPTER PAYLOAD


• EQUIPMENT

DATA ACQUISITION

• FLIGHT






• LAND USES

CONCLUSIONS


FLIGHT CONSIDERATIONS:

• AREA COVERED: 8760 m2

• FIELD OF VIEW OF THE CAMERA: 50ºx40º

• OVERLAP BETWEEN STRIPS: 50%

FLIGHT PARAMETERS:

• FLIGHT HEIGHT: 50 meters

• NUMBER OF STRIPS: 4

• FLIGHT SPEED: 5 m/s

5 minutes flight

14000 thermographies


• EQUIPMENT

DATA ACQUISITION

• FLIGHT






• LAND USES

CONCLUSIONS


DISTORTION CORRECTION

•CAMERA CALIBRATION

IMAGE REGISTRATION

•TIE POINTS BETWEEN THERMOGRAPHIES

•CORRELATION VALUE

•PROPRIETARY SOFTWARE

OVERLAPPING AREA CALCULATION

•AVOID EDGE SEAM

•LINEAR TRANSITION METHOD


• EQUIPMENT

DATA ACQUISITION

• FLIGHT






• LAND USES

CONCLUSIONS


1. DISTORTION CORRECTION

> Remove RADIAL DISTORTION introduced by the camera

> CAMERA: high distortion coefficients due to the SMALL FOCAL LENGTH of the lens (10mm)

> Camera calibrated with a CALIBRATION FIELD BASED ON EMISSIVITY DIFFERENCES

PRIOR CORRECTION POST CORRECTION


• EQUIPMENT

DATA ACQUISITION

• FLIGHT






• LAND USES

CONCLUSIONS


1. DISTORTION CORRECTION

> CAMERA: high distortion coefficients due to the SMALL FOCAL LENGTH of the lens (10mm)

CALIBRATION PARAMETER VALUE

Pixel size (mm/pix) 0,0156

Format size (mm) 5,9997 (W) * 4,5000 (H)

Principal point (mm) Xp 2,8807

Yp 2,2891

Radial distortion K1 -0,1142

K2 2,924 e-3

K3 0

Tangential distortion Px -1,813 e-4

Py -9,998 e-5


• EQUIPMENT

DATA ACQUISITION

• FLIGHT






• LAND USES

CONCLUSIONS


2. IMAGE REGISTRATION

•TIE POINTS BETWEEN THERMOGRAPHIES

•CORRELATION VALUE

•PROPRIETARY SOFTWARE

Manual marking of tie points: 4 per thermography

Computation of the CORRELATION VALUE: refine tie points position

REGISTERED IMAGE


• EQUIPMENT

DATA ACQUISITION

• FLIGHT






• LAND USES

CONCLUSIONS


3. OVERLAPPING AREA CALCULATION

•AVOID EDGE SEAM

•LINEAR TRANSITION METHOD Computation of OVERLAPPING AREA depending on its position in each thermography:

𝑀𝑖 =𝑋𝑚𝑎𝑥 − 𝑋𝑖

𝑋𝑚𝑎𝑥 − 𝑋𝑚𝑖𝑛∙ 𝐴𝑖 + 1 −

𝑋𝑚𝑎𝑥 − 𝑋𝑖

𝑋𝑚𝑎𝑥 − 𝑋𝑚𝑖𝑛∙ 𝐵𝑖

Image A Image B Image M


• EQUIPMENT

DATA ACQUISITION

• FLIGHT






• LAND USES

CONCLUSIONS


THERMOGRAPHIC DIGITAL TERRAIN MODEL

DIGITAL TERRAIN MODEL

THERMOGRAPHIC + VISIBLE FUSION

ORTHOIMAGE

Georeferencing through the coordinates of CONTROL POINTS


• EQUIPMENT

DATA ACQUISITION

• FLIGHT






• LAND USES

CONCLUSIONS


THERMOGRAPHIC DIGITAL TERRAIN MODEL

INFORMATION ABOUT ELEMENTS ON THE GROUND GEOMETRIC INFORMATION ABOUT THE SURFACE

CLASSIFICATION ON LAND USES

DEPENDING ON THEIR TEMPERATUREAREAS AND DISTANCES

CALCULATION

1 2


• EQUIPMENT

DATA ACQUISITION

• FLIGHT






• LAND USES

CONCLUSIONS


LAND USES DEPENDING ON THEIR TEMPERATURE

PIXEL SEGMENTATION > Conversion of the image from RGB color space to XYZ color space

> Classification according to X-Z values (chromaticity)

> Removal of incorrectly classified pixels (colour value threshold)

Cluster 1 Cluster 2 Cluster 3

1


• EQUIPMENT

DATA ACQUISITION

• FLIGHT






• LAND USES

CONCLUSIONS


AREAS CALCULATION - pixel size: 25cm

Cluster 1

Low Vegetation (grass)

211840 pixels

13240 m2

Cluster 2

Tall Vegetation (bushes, trees)

128800 pixels

8050 m2

Cluster 3

Metal Roofs

74400 pixels

4650 m2

2

< 5% error


• EQUIPMENT

DATA ACQUISITION

• FLIGHT






• LAND USES

CONCLUSIONS


- METHODOLOGY FOR THE GENERATION OF A THERMOGRAPHIC DIGITAL TERRAIN MODEL

- Using a LOW-COST AERIAL PLATFORM (copter type)

- Allowing the performance of analysis:

- THERMOGRAPHY: classification of land uses

detection of building prints

detection of faults in roofs

- GEOMETRY: quantification of forest masses

surface calculation per land use

calculation of heat losses of buildings

- Verification of surfaces with reality using NATIONAL CARTOGRAPHY


• EQUIPMENT

DATA ACQUISITION

• FLIGHT






• LAND USES

CONCLUSIONS


- FUTURE WORK:

EXPLOITATION OF THE THERMOGRAPHIC DIGITAL TERRAIN MODEL

- Extraction of parameters of interest:

- Coordinates of BUILDINGS

- Evaluation of HEAT ISLANDS

- Identification of TREE SPECIES

- Detection of BURIED OBJECTS


• EQUIPMENT

DATA ACQUISITION

• FLIGHT






• LAND USES

CONCLUSIONS


- REFERENCES:

1. S. Lagüela, H. González-Jorge, J. Armesto, J. Herráez, High performance grid for the metric calibration of thermographic

cameras, Measurement Science and Technology, 23(1), 2012, 9pp.

2. S. Lagüela, J. Armesto, P. Arias, J. Herráez, Automation of thermographic 3D modelling through image fusión and

image matching techniques”, Automation in Construction, 27, 24-31, 2012.

3. CIE, Colorimetry. CIE Publication 15.2, 2nd Ed, 1986, 19-20, 56-58.

4. Wiki Mikrokopter: www.mikrokopter.de

AERIAL THERMOGRAPHY FROM LOW-COST UAV FOR THE GENERATION OF

THERMOGRAPHIC DIGITAL TERRAIN MODELS

S. Lagüela, L. Díaz-Vilariño, D. Roca, J. Armesto

Applied Geotechnologies Research Group, University of Vigo (Spain)

Corresponding Author: [email protected]

S. Laguela - Aerial thermography from low-cost UAV for the generation of thermographic digital...

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