===!"§ deutsche telekom laboratories target acquisition with camera phones when used as magic...
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===!"§Deutsche Telekom Laboratories
Target Acquisition with Camera Phoneswhen used as Magic LensesCHI 2008, Florence, Italy, April 9, 2008
Michael Rohs
Deutsche Telekom LaboratoriesTechnische Universität Berlin
Antti Oulasvirta
Helsinki Institute for Information Technology HIIT
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Deutsche Telekom Laboratories
See-Through Interfaces for Camera Phones
Augmented reality (AR) applications project information onto real world scenery in real time
—Camera phone shows this layer through narrow viewport
Navigation by moving the device—Spatially-aware displays [Fitzmaurice]—Peephole displays [Yee]
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Magic Lens for AR Widgets
Printable user interface elements
—Embedded in user’s environment
—Entry point for interaction—Controlled via position, rotation,
distance Background layer
—Passive widget Overlay layer
—Active Display—Camera phone as “see-through
tool”
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Dynamic Peephole Pointing & Magic Lens Pointing
Dynamic peephole pointing
Movement of peephole corresponds to movement through virtual space
No visual context beyond display
Targets dynamically revealed
Magic lens pointing Camera phone tracks its
position above a meaningful background
Visual context beyond display
Targets always visible
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Target Acquisition with Camera Phones
Two distinct categories of interfaces—Dynamic peephole: Objects of interest only in virtual—Magic lens: Objects of interest on the physical surface
Analyzing target acquisition with camera phones—Performance—Modeling
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Overview
Analysis of the Pointing Tasks Two-Component Model of Magic Lens Pointing Experiment 1: Dynamic Peephole Pointing Experiment 2: Magic Lens Pointing
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Target Acquisition with Camera Phones
View selection Screen distance range System delay Maximum movement velocity Display update rate Device movement in 3D space Gaze deployment between display and
background
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Analysis of Dynamic Peephole Pointing Task
Task: Move cursor onto target
Target might not be visible in the peephole initially Visual feedback uniformly mediated by the device
Hypothesis: Dynamic peephole pointing can be modeled by Fitts’ law
MT = ao + bo ID with ID = log2(D / W + 1)
Lag and low frame rates increase the coefficients ao and bo compared to direct observation of the target
W
D
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Analysis of Magic Lens Pointing Task
Task: Move cursor onto target
First phase: Target directly visibleFirst task: Move lens over target
Second phase: Target behind displaySecond task: Move crosshair over target
T
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Analysis of Magic Lens Pointing Task
Task: Move cursor onto target
First phase: Target directly visibleMTp = ap + bp log2(D / S + 1)
Second phase: Target behind displayMTv = av + bv log2(S/2 / W + 1)
S W
W
S/2
D
T
S
D
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Magic Lens Pointing Model
First phase (physical pointing): MTp = ap + bp log2(D / S + 1)
Second phase (virtual pointing): MTv = av + bv log2(S/2 / W + 1)
Two-component Fitts’ law modelMT = MTp + MTv
= a + b log2(D / S + 1) + c log2(S/2 / W + 1)
S W
D
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physical pointing
Control Loops in Physical Pointing
Iterative corrections model [Crossman & Goodeve]
—Derive Fitts’ law from number of iterations through feedback loop
—Movements >200 ms controlled by visual feedback—Ballistic submovements of constant time (135-290 ms)—Each submovement has distance error (4-7%)
observe target distance P = 100 ms
plan hand movement C = 70 ms
perform hand movement M = 70 ms
expected distance error
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Control Loops in Virtual Pointing
Virtual pointing introduces delay in feedback loop
Machine lag and frame rate [Ware & Balakrishnan]
Time for submovement t = P + C + M and machine lag L
Rewrite two-part model asMT = a + β t log2(D / S + 1) + γ (t + L) log2(S/2 / W + 1) observe target distance
P = 100 ms
plan hand movement
perform hand movement
expected distance error
C = 70 ms
M = 70 ms
virtual pointingcompute device position
L = 100–300 ms
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Dynamic Peephole Pointing Experiment
Targets only visible on device display Device tracked on surface of size A0 Cyclical multi-direction target acquisition
(ISO 9241-9) 9 targets on a circle, next one highlighted Nokia N80 for tracking and feedback (beeps, highlighting) 12 participants (10 male, 2 female, age 22-33) Task: Move crosshair over target and press joystick
button Instructed to calibrate z-distance and explore space
before start W = 13-97 mm, D = 55-535 mm, 33 combinations
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Results of Dynamic Peephole Pointing
12 subjects x 33 conditions x 3 rounds x 9 selections
Mean movement time: 2.13 sec Mean error rate: 5%
0%
5%
10%
15%
20%
0 1 2 3 4 5 6 7 8 9 10
W [cm]
erro
r ra
te
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Fitts’ Law Model of Dynamic Peephole Pointing
Basic Fitts’ law leads to accurate predictions MT = a + b log2(D / W + 1)
= -636 + 881 log2(D / W + 1), R2 = 0.93
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5ID
MT
[se
c]
MT = a + b log2 (D / W + 1)
a = 0.636, b = 0.881R2 = 0.93
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.50
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
ID
MT
[se
c]
-
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Magic Lens Pointing Experiment
Targets visible on background and through lens Device tracked on plasma display of size A0 Cyclical multi-direction target acquisition
(ISO 9241-9) 9 targets on a circle, next one highlighted Nokia 6630 for tracking and feedback (beeps,
highlighting) 12 participants (8 male, 4 female, age 19-31) Task: Move crosshair over target and press joystick
button Instructed to calibrate z-distance before start W = 13-97 mm, D = 55-535 mm, 33 combinations
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Results of Magic Lens Pointing
12 subjects x 33 conditions x 3 rounds x 9 selections
Mean movement time: 1.22 sec Mean error rate: 7%
0%
5%
10%
15%
20%
0 1 2 3 4 5 6 7 8 9 10
W [cm]
erro
r ra
te
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Fitts’ Law Model of Magic Lens Pointing
Fitts’ law does not accurately predict performance
MT = 581 + 191 log2(D / W + 1), R2 = 0.57
0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.50
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
2
ID
MT
[sec
]
MT = a + b log2 ( D / W + 1)a = 0.581, b = 0. 191R2 = 0.57
MT
[sec
]
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Two-Part Fitts’ Law Model of Magic Lens Pointing
Two-component Fitts’ law leads to better prediction
Screen diagonal S = 2.8 cm MT = a + b log2(D / S + 1) + c log2(S/2 / W +
1)= 383 + 112 log2(D / S + 1) + 811
log2(S/2 / W + 1), R2 = 0.88
1 1.2 1.4 1.6 1.8 2
1
1.2
1.4
1.6
1.8
2
predicted MT [sec]
mea
sure
dM
T [s
ec]
MT = a + b log2 (D / S + 1) + c log2(S/2 / W)
S = 2.8 cma = 0.383, b = 0.112, c = 0.811
R2 = 0.88
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Two-Part Fitts’ Law Model with Parameters a, b, c, S
Treating lens size S as an additional parameter MT = 384 + 113 log2(D / 2.99 + 1)
+ 776 log2(2.99/2 / W + 1), R2 = 0.88
Screen diagonal predicted to 2.99 cm (real value 2.8 cm)
Supports the validity of the model
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Conclusion
Analyzed target acquisition with camera phones as—Dynamic peephole displays—Magic lenses
Dynamic peephole pointing can be modeled with Fitts’ law—Interaction uniformly mediated by the device
Magic lens pointing not adequately explainable by Fitts’ law
—Initial physical pointing phase—Second virtual pointing phase
Developed two-part Fitts’ law model for magic lens pointing
—MT = a + b log2(D / S + 1) + c log2(S/2 / W + 1)
Numerous application ideas for magic lens interfaces