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AUG - Augmented Reality > 04 - Tracking Foundations und Optical Tracking > Flashcards

04 - Tracking Foundations und Optical Tracking Flashcards

(54 cards)

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1
Q

Warum braucht man Tracking Systeme?

A

Die Idee der Tracking systeme ist es die Position und Orientierung eines reelen Objekts zu messen, um virtuelle Objekte besser mappen zu können

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2
Q

Für was wird Tracking in der AR verwendet?

A
  • Augmentations anzeigen
  • Interaktion
  • Lokalisation vom User und Device
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3
Q

Welche Arten von Tracking gibt es in der AR?

A
  • Tracken von Objekten
  • Tracken von Features
  • Tracken der Kameraposition
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4
Q

Was gehört in der AR noch zum Tracking?

A

Calibration und Registration

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5
Q

Welche Trackingsysteme werden nur wenig in AR, dafür vermehrt in VR verwendet?

A
  • Mechanische
  • Magnetische
  • Akustische
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6
Q

Welche generellen Registrierungsprobleme gibt es?

A

 In AR objects of real and virtual world have to be aligned with respect to each other

 Humans are very sensible to visual errors

 Registration issues in VR are harder to detect, basically one of the causes of cybersickness (visual-kinaesthetic and visual-proprioceptive conflict)

 Visual capture decreases the issues related to registration errors in VR

 Errors of a few pixels offset on the other hand are easily detectable in AR applications

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7
Q

Welche statischen Fehler gibt es bei der Registrierung?

A

 Registration error if the viewpoint and the environment remain still
 Causes
 Optical distortion - if camera tracking is used
 Errors in the tracking system - mechanical misalignments or offset of tracker and head
 Incorrect viewing parameters - Field Of View (FOV) - Interpupillary distance (IPD) -> Abstand zwischen Augen, muss mitberücksichtigt werden

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8
Q

Welche dynamischen Fehler gibt es bei der Registrierung und was kann man dagegen tun?

A

 Registration error during viewpoint and/or environment movement

 Causes
 Delays or lags

 Overcoming dynamic errors
 Reduce system lag - efficient algorithms and parallel computation
 Reduce apparent lag - simplification of scenes
 Match temporal streams - use of video information gathered from optical tracking
 Predict future locations - help of accelerometers –prediction based on sensor speed and orientation (Wo wird sich User hinbewegen? Dann werden dafür vorberechnungen durchgeführt

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9
Q

Was ist Jitter?

A

Zittern bei der Latenz

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10
Q

Welche Jitter Fehler gibt es bei der Registrierung und was kann man dagegen tun?

A

 Depending on used library even with static markers and static camera virtual objects could jump

 Multiple reasons exist
 Discretisation in the rasterisation process (optical tracking)
 Jitter can be avoided through smoothing algorithms
 Detection of larger jumps could point to an error

 Potential solution
 If 3rd measurement is in range of 1st measurement interpolation of 2nd could be performed by using 1st and 3rd measurement as base

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11
Q

Was ist Inertial Tracking und wie ist es aufgebaut?

A

 Typically consists of 2 components
 Gyroscopic compass
 Accelerometer
 Often used in combination with other tracking technology to provide additional information (e.g., optical, acoustic)

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12
Q

Was sind Vorteile von Interial Tracking?

A

 No stationary tracking
 Useful in large indoor areas where no other tracking is possible (e.g., buildings, caves)
- Kann verwendet werden wenn kein anderes Trackingsystem möglich ist

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13
Q

Was sind Nachteile von Intertial Tracking?

A

 Accumulating position errors

 Orientation stays precise if compasses are used

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14
Q

Wie funktioniert dabei das Intertiall Sensing?

A

 Provides information about relative transformations of a target

 Attempt to conserve either a given axis of rotation as in the case of a mechanical gyroscope or a position as in the case of an accelerometer

 Mechanical gyroscope
 A system based on the principle of conservation of the angular momentum
 It states that an object rotated at high angular speed in the absence of external moments, conserves its angular momentum

 If torque is exerted on a spinning mass, its axis of rotation will precess at right angles to both itself and the axis of exerted torque

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15
Q

Wie funktioniert das Intertial Sensing mit Accelerometer?

A

 Measures the linear acceleration of an object to which it is attached to
 Actually measures the force exerted on a mass since we cannot measure acceleration directly
 Uses a known mass (proof mass) attached to a spring
 Other end is attached to the accelerometers casing
 If no force is applied, spring is in rest position
 If force on the casing is applied, inertia causes mass to move and extend or compress spring
 The displacement of the mass and extension/compression of the spring is proportional to the acceleration of the housing
 Types of measurement sensors are potentiometric and piezoelectric

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16
Q

Wie funktioniert das Intertial Sensing mit Accelerometer?

A

 Measures the linear acceleration of an object to which it is attached to
 Actually measures the force exerted on a mass since we cannot measure acceleration directly
 Uses a known mass (proof mass) attached to a spring
 Other end is attached to the accelerometers casing
 If no force is applied, spring is in rest position
 If force on the casing is applied, inertia causes mass to move and extend or compress spring
 The displacement of the mass and extension/compression of the spring is proportional to the acceleration of the housing
 Types of measurement sensors are potentiometric and piezoelectric

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17
Q

Wie können beim Inertial Tracking Accelerometers und Gyroscpoes kombiniert werden?

A

 Mechanical sensing

 Placement on a gimbal locked surface

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18
Q

Was sind die Vorteile von kombiniertem Inertial Tracking?

A

 Provides 6DOF acceleration and orientation measurement
 Be always aware of the accumulative error
 Measurements are always relative to last position

 Can be a useful addition to other tracking technologies to increase the precision

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19
Q

Was ist GPS und wie wird es verwendet?

A

 Originally military development

 Now widely used in civil sector (e.g., navigation systems, precision farming, hiking, biking, geocaching)

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20
Q

Wie funktioniert GPS?

A

 Satellites constantly send position and time values
 Overlap of three spheres results in two points (one in space and one earth)
 In theory reception of signals from three to four satellites required for trilateration and clock precision

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21
Q

Welche Frequenzen werden von GPS verwendet?

A

 L1 – CA Coarse/acquisition

 L2 – PY Precision/encrypted

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22
Q

Welche Alternativen gibt es zu GPS?

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A

GLONASS (Russian), Galileo (Europe), MTSAT (Japan), Compass (China)

23
Q

Welche Vorteile hat GPS?

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A

Globale Tracking Area

24
Q

Welche Nachteile hat GPS?

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A

Himmel muss sichtbar sein

Verdeckungen von Häusern/Bäumen

25
Was ist optical Tracking?
 Vast amount of possibilities  Use of different types of markers (e.g., active, passive)  Use of image processing to analyse the real world information (e.g. landmark recognition)  Inside Out vs. Outside In
26
Wie funktioniert Optical Tracking mit Infrarotlicht?
 IR camera to track printed marker or IR sources  Commercial systems tend to be expensive, due to the required high quality camera equipment  No bright surroundings needed / desired  Collision with other IR light sources might occur (e.g., stereo emitters, sunlight)  Possibility to place IR sources in the surroundings, recording in that case might take place from a camera attached to a user
27
Welche 2 Varianten von Spatial Scan (klassische Verfahren) beim Optical Tracking gibt es?
 Videometric |  Beam scanning
28
Was ist Videometric Optical Tracking?
 Example setup with sequentially fired LED patterns on the ceiling  Tracked with four cameras mounted on a users helmet
29
Was ist Beam scanning Optical Tracking?
 Scanning optical beams on a reference |  Sensors located on the target detect the time of sweep of the beams on their surface
30
Welche Verfahren werden heute hauptsächlich verwendet?
- Pattern recognition | - Matrix Code
31
Wie funktioniert Pattern recognition?
 Only one camera is needed  Shape and size of the object to be recognised are known beforehand to the system  The recorded 2D pattern on the image is a function of the position and orientation of the target  Most common approach using pattern recognition is fiducial tracking implemented for example in ARToolKit or in Vuforia  Another early approach is the Matrix Code by Rekimoto
32
was ist Matrix Code?
 Also known as CyberCode, first used in NaviCam project  Square shaped barcode that can identify and distinguish 216 possible markers  Matrix markers attached on real-world objects  Based on object and pattern recognition  Markers are attached to moving objects  Camera at a fixed position recording images of markers  Marker could be fixed and camera movable or both camera and markers are movable
33
Wie funktioniert Matrix Code?
 After image is recorded (a) thresholding and binarisation are performed (b)  Connected components are identified (c) in order to detect and identify markers  Based on identified marker position, orientation, size and type the virtual object can be drawn on top or relative to the marker (d)
34
Welche Probleme gibt es bei Matrix Code?
 Computationally intense  Line of sight to the camera  Bright surroundings might be necessary
35
Wie können zum Optical Tracking reflektive Marker verwendet werden?
 Common concept to use reflective marker configuration  Reflect IR light emitted by IR LEDs  Marker configurations are recorded by cameras configured to only record IR light  Conflicts with other IR sources might occur (e.g. sync from shutter glasses, Kinect)
36
Was ist JanusVF?
 Inside-Out tracking looks at projected fiducial patterns  Provides a closed loop between recognition and display of targets  Uses Single-Constraint-At-A-Time (SCAAT), Extended Kalman Filter (EKF), and ARToolKit Plus  Tracking data is provided to the system via VRPN  Restricted usage in 6 sided CAVEs  Very limited application field  Precise and cheap tracking method Man projiziert Muster was man zum Tracken verwendet hinter sich in eine Cave und nimmt es mit einer Kamera auf
37
Welche Algorithmen verwenden Tracking Systeme ohne Marker?
SLAM
38
Was ist SLAM?
● Odometry is the use of data from the movement of actuators to estimate change in position over time (Man zeichnet Raum mit Landmarks (Kanten, Ecken) auf) ● Simultaneous Localisation And Mapping (SLAM)  Idea behind SLAM  Place a robot at an unknown location in an unknown environment  Have the robot build a map of the environment  Use the map to compute the robots location
39
Aus welchen Schritten besteht SLAM?
```  Landmark extraction  Data association  State estimation  State update  Landmark update ```
40
Wie funktioniert das Erkennen von SLAM Landmarks?
 Objects that can be recognized over and over again  The objects should be re-observable, distinguishable from each other and stationary  Type of measurement can be based on different technology, e.g. spatial scan, TOF
41
Welche Algorithmen werden zur SLAM Landmark Extraction verwendet?
- Spike landmarks | - RANdom SAmpling Consensus (RANSAC)
42
Welche Probleme können beim SLAM Landmark Extraction auftreten?
 Matching observed landmarks from different scans  Problems that might occur  Might not re-observe landmarks every time step  Might observe something as being a landmark but fail to ever see it again  Might wrongly associate a landmark to a previously seen landmark  Possibility to take close-by landmarks into account (e.g. checking Euclidian distance)
43
Was wird für die SLAM State Estimation verwendet?
- Kalman Filter | - Used to build a “stochastic map” of spatial relationships
44
Was passiert beim SLAM State Update?
 Estimate we obtained for the robot position is not completely exact due to the odometry errors  Using the associated landmarks we can now calculate the displacement
45
Was passiert beim SLAM Landmark Update?
 Update the state vector X and the covariance matrix P in the EKF  Purpose is to have more landmarks that can be matched, so the robot has more landmarks that can be matched
46
Was sind typische Anwendungsfelder von SLAM?
 Robots (e.g. vacuum cleaners)  AR Tracking in general  Panoramic images
47
Welche Verfahren gibt es zum 3D Depth Sensing und wozu wird es verwendet?
- Stereo Cameras - Traingulation - Structured Light - Time of Light Um 3D Modelle zu erhalten
48
Wie funktioniert im 3D Depth Sensing Stereo Cameras?
 Two displaced cameras observe different views of the scene  Depth is calculated based on relative positions of the object or feature perceived in the two cameras images
49
Wie funktioniert im 3D Depth Sensing Triangulation?
 Laser projection of dot or line into the scene  Displacement of laser projector to the camera is known  Based on the perceived camera image location of the hit point can be calculated  Precise measurements possible
50
Wie funktioniert im 3D Depth Sensing Structured Light?
 Fixed or variable pattern is projected in the scene  Projected pattern is recorded again by camera system  Distortion of the pattern can be perceived and used to determine the structure of the object it is projected on
51
Wie funktioniert im 3D Depth Sensing Time of Flight?
 Measurement of the time from emitting light to the reflection of emitted light  Delay determines the distance  Calculation based on speed of light
52
Was ist Visual Inertial Odometry?
● Combination of SLAM-like approaches with inertial tracking ● Inertial tracking is in that case used to support the visual odometry ● Sensor fusion algorithms ● Current tending approach for tracking ● General problem with visual odometry is motion blur during fast movements
53
Wie können Szenen/Räume durch Tracking rekonstruiert werden?
● Current devices use IR time-of-flight tracking (HoloLens) or IR structured light (iPhone X) for reconstruction ● Only very rough depth maps available in real time ● Re-meshing required, points have to be interconnected
54
Wofür werden Raumrekonstruktionen verwendet?
 Placement of augmentations in the scene  Tracking purposes  Generation of virtual objects  Advanced rendering techniques like occlusion handeling

AUG - Augmented Reality (7 decks)

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