euclidean position estimation of features on a static object using a moving calibrated camera...
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EUCLIDEAN POSITION ESTIMATION OF FEATURES ON A STATIC OBJECTEUCLIDEAN POSITION ESTIMATION OF FEATURES ON A STATIC OBJECT USING A MOVING CALIBRATED CAMERA USING A MOVING CALIBRATED CAMERA
Nitendra Nath, David BraganzaNitendra Nath, David Braganza‡‡, and Darren Dawson, and Darren DawsonDepartment of Electrical and Computer Engineering, Clemson University,
Clemson, SC 29634-0915, E-mail: [email protected]
AbstractAbstract
What is Euclidean Position Estimation?What is Euclidean Position Estimation?•Three-dimensional (3D) reconstruction of an object, where the Euclidean coordinates of feature points on a moving or fixed object are recovered from a sequence of two-dimensional (2D) images is known as Euclidean position estimation or more broadly known as Structure from Motion (SFM) or Simultaneous Localization and Mapping (SLAM).
•They have significant impact on several applications such as:
•A 3D Euclidean position estimator using a single moving calibrated camera whose position is assumed to be measurable is developed in this paper to asymptotically recover the structure of a static object.
•To estimate the structure, an adaptive least squares estimation strategy is employed based on a novel prediction error formulation and a Lyapunov stability analysis.
Autonomous vehicle navigation Path planning Surveillance
Geometric ModelGeometric ModelA geometric relationship is developed between a moving camera and a stationary object. n feature points located on a static object , denoted by are considered.
¹mi , [xi yi zi ]T
F i 8 i =1;:::;n
3D coordinates of ith feature point w.r.t. :C
Normalized Euclideancoordinates :
mi , 1zi¹mi = [xi=zi yi=zi 1]T
Corresponding projected pixel coordinates : pi , [ui vi ]T
,ui (t) 2 R vi (t) 2 R
Pin-hole camera model: pi =Ami =1ziA ¹mi
A ,·f ku f ku cotÁ u00 f kv
sin Á v0
¸
: Known constant intrinsic calibration matrix of the camera
A 2 R2£ 3
The objective of this work is to accurately identify the unknown constant Euclidean coordinates of the feature xfi relative to the world frame in order to recover the 3D structure of the object.
Geometric relationships between the fixed object, mechanical system and the camera.
Rb(t) 2 SO(3)
xb(t) 2 R3
Rc(t) 2SO(3)xc(t) 2R3
Measurable rotation matrix and translation vector from B to W
Known constant rotation matrix and translation vector from C to B
xf i 2 R3
¹mi (t) 2 R3 Unkown
Euclidean Structure EstimationEuclidean Structure EstimationFrom the geometric model, the following expression can be obtained: ¹mi =RT
c
£RTb (xf i ¡ xb) ¡ xc
¤
After utilizing pin-hole camera model, pixel coordinates of ith feature point can be written as:
pi = 1ziART
c
£RTb (xf i ¡ xb) ¡ xc
¤
Corresponding depth
zi =RTc3
£RTb (xf i ¡ xb) ¡ xc
¤
Last row of RTc (t)
in parameterized form: pi (t) pi = 1¦ £ i
W£ i
W£ i =ARTc
£RTb (xf i ¡ xb) ¡ xc
¤¦ £ i = zi = RT
c3
£RTb (xf i ¡ xb) ¡ xc
¤,
Prediction errorfor ith feature point
~pi = 1¦ £ i
(W ¡ p̂i ¦ )~£ i
Combined prediction error
~p=B ¹Wp~£
¦ (t) 2 R1£ 4, W (t) 2 R2£ 4 : measurable regression matrices £ i 2 R4 : unkown constant parameter vector
¹Wp (t) 2 R2n£ 4n
B (t) 2 R2n£ 2n
~£ (t) 2 R4n
: measurable signal: auxiliary matrix: combined estimation
error
Adaptive update law is designed as::
£̂ , Proj©®¡ ¹WT
p ~pª Proj f¢g
®(t) 2 R
¡ (t) 2 R4n£ 4n
: ensures positiveness of the term ¦ (t) £̂ i (t)
: a positive scalar function
: least-squares estimation gain matrix
Simulation ResultsSimulation Results
0 5 10 15 20 25 30 35 40 45 50-50
0
50
100
150
200
250
300
[sec]
[cm
]
0 5 10 15 20 25 30 35 40 45 50-50
0
50
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300
[sec]
[cm
]
0 5 10 15 20 25 30 35 40 45 50-50
0
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200
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[sec]
[cm
]
Case 1: No noise added to pixel coordinates
Distance Estimation Error
Object Actual distance (cm) Estimated distance (cm) Error (cm) Convergence time (sec)
Case 1
Length ILength II
Length III
50.0
111.8
100.0
49.94
111.25
99.86
0.06
0.55
0.14
0.12
0.49
0.14
Case 2
Length ILength II
Length III
50.0
111.8
100.0
49.90
111.15
99.74
0.10
0.65
0.26
0.20
0.58
0.26
Case 3
Length ILength II
Length III
50.0
111.8
100.0
49.88
111.08
99.65
0.12
0.72
0.35
0.24
0.64
0.35
Experimental ResultsExperimental Results
Case 2: Gaussian noise of variance 200 added to pixel
coordinates
Case 3: Gaussian noise of variance 400 added to pixel
coordinates
Robot Control PC Vision PC
15 Hz Trigger PUMA 560 RobotObject
Monochrome CCD Camera
Experimental testbed with camera, robot
and object
0 10 20 30 40 50 60-100
0
100
200
300
400
500
600
[sec]
[cm
]
Object Actualdistance (cm)
Estimated distance (cm)
Error (cm)
Convergence time (sec)
Length ILength IILength IIILength IVLength VLength VI
11.242.8111.245.6216.865.62
11.412.7611.565.7217.315.44
0.170.050.320.100.450.18
37.333.133.332.237.635.4
Object I: Checker-board Distance Estimation Error
Object II: Doll-house
0 10 20 30 40 50 60-200
0
200
400
600
800
1000
1200
1400
1600
1800
[sec]
[cm
]
Distance Estimation Error
Object Actualdistance (cm)
Estimated distance (cm)
Error (cm)
Convergence time (sec)
Length ILength IILength IIILength IVLength VLength VI
40.012.212.213.015.026.5
41.312.711.613.414.327.4
1.30.50.60.40.70.9
32.233.430.132.234.733.5
Object III: Tool-boxes
0 10 20 30 40 50 60-50
0
50
100
150
200
250
300
350
400
[sec]
[cm
]
Distance Estimation Error
Object Actualdistance (cm)
Estimated distance (cm)
Error (cm)
Convergence time (sec)
Length ILength IILength IIILength IVLength VLength VI
14.74.25.09.09.63.8
14.154.104.968.789.443.64
0.550.100.040.220.160.16
37.639.936.739.839.838.9
The estimator accurately identifies the Euclidean distances between the features without having any information with regard to the object’s geometry.
‡ D. Braganza is with OFS, 50 Hall Road, Sturbridge, MA 01566.
KLT feature tracking algorithm was used for tracking feature points from one frame to another.