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

04 - Tracking Foundations und Optical Tracking Flashcards

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?

A

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

23
Q

Welche Vorteile hat GPS?

A

Globale Tracking Area

24
Q

Welche Nachteile hat GPS?

A

Himmel muss sichtbar sein

Verdeckungen von Häusern/Bäumen

25
Q

Was ist optical Tracking?

A

 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
Q

Wie funktioniert Optical Tracking mit Infrarotlicht?

A

 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
Q

Welche 2 Varianten von Spatial Scan (klassische Verfahren) beim Optical Tracking gibt es?

A

 Videometric

 Beam scanning

28
Q

Was ist Videometric Optical Tracking?

A

 Example setup with sequentially fired LED patterns on the ceiling
 Tracked with four cameras mounted on a users helmet

29
Q

Was ist Beam scanning Optical Tracking?

A

 Scanning optical beams on a reference

 Sensors located on the target detect the time of sweep of the beams on their surface

30
Q

Welche Verfahren werden heute hauptsächlich verwendet?

A
  • Pattern recognition

- Matrix Code

31
Q

Wie funktioniert Pattern recognition?

A

 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
Q

was ist Matrix Code?

A

 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
Q

Wie funktioniert Matrix Code?

A

 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
Q

Welche Probleme gibt es bei Matrix Code?

A

 Computationally intense
 Line of sight to the camera
 Bright surroundings might be necessary

35
Q

Wie können zum Optical Tracking reflektive Marker verwendet werden?

A

 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
Q

Was ist JanusVF?

A

 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
Q

Welche Algorithmen verwenden Tracking Systeme ohne Marker?

A

SLAM

38
Q

Was ist SLAM?

A

● 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
Q

Aus welchen Schritten besteht SLAM?

A 
 Landmark extraction 
 Data association 
 State estimation 
 State update 
 Landmark update
40
Q

Wie funktioniert das Erkennen von SLAM Landmarks?

A

 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
Q

Welche Algorithmen werden zur SLAM Landmark Extraction verwendet?

A
  • Spike landmarks

- RANdom SAmpling Consensus (RANSAC)

42
Q

Welche Probleme können beim SLAM Landmark Extraction auftreten?

A

 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
Q

Was wird für die SLAM State Estimation verwendet?

A
  • Kalman Filter

- Used to build a “stochastic map” of spatial relationships

44
Q

Was passiert beim SLAM State Update?

A

 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
Q

Was passiert beim SLAM Landmark Update?

A

 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
Q

Was sind typische Anwendungsfelder von SLAM?

A

 Robots (e.g. vacuum cleaners)
 AR Tracking in general
 Panoramic images

47
Q

Welche Verfahren gibt es zum 3D Depth Sensing und wozu wird es verwendet?

A
  • Stereo Cameras
  • Traingulation
  • Structured Light
  • Time of Light

Um 3D Modelle zu erhalten

48
Q

Wie funktioniert im 3D Depth Sensing Stereo Cameras?

A

 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
Q

Wie funktioniert im 3D Depth Sensing Triangulation?

A

 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
Q

Wie funktioniert im 3D Depth Sensing Structured Light?

A

 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
Q

Wie funktioniert im 3D Depth Sensing Time of Flight?

A

 Measurement of the time from emitting light to the reflection of emitted light
 Delay determines the distance
 Calculation based on speed of light

52
Q

Was ist Visual Inertial Odometry?

A

● 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
Q

Wie können Szenen/Räume durch Tracking rekonstruiert werden?

A

● 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
Q

Wofür werden Raumrekonstruktionen verwendet?

A

 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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