3D Vision and Imaging March 27th, 2014
[email protected]
Time of flight moves, ... ToF !
What if the ToF camera or objects in the scene are moving ?
Notes, questions, remarks …
TETRA-project: SMART DATA CLOUDS (2014 – 2016) .
Contact persons:
[email protected] [email protected] [email protected]
Website: https://www.uantwerpen.be/op3mech/
TETRA: Smart Data Clouds (2014-2016): a. Security, track and trace b. Traffic control and classifications c. (Smart) Navigation d. Dynamic 3D body scan
industrial cases
[Haven van Antwerpen]. [Macq, LMS, Melexis] [Wheelshairs, PIAM, mo-Vis, Automotive LMS] [RSscan, ICRealisations]
Data Fusion: ind. Vision linked with CAE.
Data from RGB, IR, ToF and HS cameras.
TETRA: Smart Data Clouds (2014-2016): a. Wheelchair control - navigation: b. Gesture & Body-analysis:
healthcare applications [mo-Vis, PIAM, Absolid] [RSScan, ICrealisation, Phaer, ODOS]
‘Data Fusion’ usable for future Healthcare .
03D2xx-cameras IFM-Electronics 64x50 pix.
PMD[Vision]CamCube 3.0 352 x 288 pix! Recent: pmd PhotonICs® 19k-S3
Swiss Ranger 4500 MESA 176 x 144 pix.
Fotonic RGB_C-Series 160 x 120 pixel Previous models: P – E series.
Melexis: EVK75301 DepthSense 325 ( 320 x 240 pix )
BV-ToF 128x120 pix.
80x60 pix.
Near Future: MLX75023 automotive QVGA ToF sensor .
ODOS: 1024x1248 pix. Real.iZ-1K vision system
Photonic Mixing Device PMD
Time of flight Measurement Principles (1/3) c = λmod * fmod λNIR = +/- 850 nm.
Light takes about 66 picoseconds to travel over 1 cm.
λmod = 15 meter ; λmod = 10 meter ;
fmod = 20 MHz fmod = 30 MHz
2.D = λmod . [φ/2π] Error = k. λmod / (√n . S/N )
Lambert : I(θ) = Imax.cos(θ)
and
Reflection factor BRDF
ωin ωscatter
‘Lambertian’ reflection law
Random texture
BRDF stands for: ‘bidirectional reflectance distribution function’ Each point of a surface has a normal direction n. Incident light from a direction ωin is scattered in all directions ωscatter . BRDF describes the angular distribution of the scattered energy fractions f(ωin , ωscatter) .
Moving ToF:
(Robotics, AGV’s, conveyor belts,… ..‘road damage inspection’)
During motion, inconsistent brightness values are collected giving rise to chaotic fluctuations on the measured phase angle ‘phi’ . Distance D = 294
Correct Distance = 285
800
Big deviations will occur !
700 600
φ = atan[(A1-A3)/(A2-A4)]
500 400
2.D = λmod . [φ/2π]
Texture dependant mean intensity values A0
300
2
1 φ
3
200 100 0
4
A1 0 100 Angle = 0.73892
A2
A3
A4
200 300 Correct angle = 0.71558
Remember: ‘pulsed time of flight cameras’ don’t follow this mechanism !
Time of flight Measurement Principles (2/3)
Correlation suppress the chaotic blur . Sine Wave Correlation
Cross Correlation between ‘send’ and ‘received’ TOF signals •
s(t) = A.cos(ω.t) . r(t) = a(t).cos[ω.(t-τ)] + b(t)
•
the ‘instant cross correlation C(x)’ depends on the integration time T and is noisy but somehow harmonic with respect to (τ+x) :
emitted signal: • received signal:
( b = ambient light )
T/2
C(x) := 1/T . ∫ r(t).s(t+x).dt = amean.A/2.cos[ω.(τ+x)] + bmean -T/2 T/2
amean = 1/T . ∫ a(t).dt -T/2
and
bmean
T/2
= 1/T . ∫ b(t).dt -T/2
• the best guess for the time shift τ is found at the maximum of C(x) . • distance measured at pixel (i,j) :
2.D(i,j) = c.τ .
(c = speed of light)
Time of flight Measurement Principles (3/3)
Square Wave Correlation
Melexis cameras use 4 instant cross correlation values: named, S0, S90, S180 and S270 .
Integration time
Correlation values
S180
Y>0 Brightness I0
Y
