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Advanced Biomechanics > Three dimensional kinematics > Flashcards

Three dimensional kinematics Flashcards

1
Q

what is 3d calibration establishing?

A

collects information to establish DLT parameters

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2
Q

DLT parameters

A

Direct linear transformation
-where cameras are
-in which directions do cameras point

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3
Q

3D analysis: Step 1

A

obtain series of vectors which describe object and image coordinates in different reference systems

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4
Q

3D analysis: Step 2

A

Make multiple vector substitutions and transformations

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5
Q

3D analysis: Step 3

A

u= (Ax+By+Cz+D)/(Ex+Fy+Gz+1)
v= (Hx+Iy+Jz+K)/(Ex+Fy+Gz+1)

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6
Q

3D analysis: Step 4

A

Calibration Experiment

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7
Q

3D analysis: Step 5

A

Final Step
2 cameras to record points at same moment in time (time-synchronus)

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8
Q

Issues with 3D calibration

A
  • ## Redundancy: number of control points vs number of cameras
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9
Q

When is Global Coordinate System determined?

A

Determined during calibration of motion analysis system

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10
Q

How is Dynamic Calibration accomplished, when is it processed?

A

Wand dance
Processed first

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11
Q

what does Static Calibration accomplish?

A

establishes constant for variable (0,0,0)

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12
Q

Residuals

A

numbers that indicate the quality of calibration

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13
Q

Linearization

A

the process of correcting for lens distortion

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14
Q

bundle adjustment

A

an algorithm that performs the linearization process by optimizing the camera parameters to give the best reprojection error

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15
Q

Dynamic calibration algorithmic assumptions

A

-known distance to orgins
-no extraneous markers
-2d marker images seen by different cameras originate from the same 3d position

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16
Q

Wand dance tips

A

-avoid breaking cameras view with body
-position body so wand can be seen by as many cameras as possible
-move around the entire volume
-collect ~1000 or more samples
*rotate and move wand up and down and back and fourth

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17
Q

Residuals limit

A

<.18

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18
Q

What does tripleton establish?

A

establishes direction of first x axis

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19
Q

What does singleton establish?

A

-establishes position of origin
-combines with first axis to establish second
resultatnt cross product is third

20
Q

Common causes of failed calibrations

A

Bad wand dance

Poor camera position

Background static noise

21
Q

Local Coordinate System Guidelines

A
  • 3 non colinear markers on segment (GTC, ASIS, PSIS)
22
Q

LCS determination (j’)

A

Sets AP axis
denominator is magnitude of difference

23
Q

LCS determination (i’)

A

Sets ML axis

24
Q

LCS Determination (k’)

A

sets longitudinal axis

25
Q

What does this image represent?

A

Static 3D coordinates of transformation matrix

26
Q

what does this formula represent?

A

rotational matrix

27
Q

Types of transformations

A
  1. linear transformations
  2. rotational transformations

*both have a rigid body assumption

28
Q

What do Linear Transformations assume?

A

no rotation

29
Q

rotational transformations

A

assumes no translations

30
Q

What do A and B represent

A

A. rotational transformation unit vector for proximal segment
B. rotational transformation unit vector for distal segment

31
Q

Methods for determining joint angles (which is primarily used in Biomechanics?)

A
  1. Cardan*/Euler
    2 Joint coordinate system
  2. Helical Axes
32
Q

Cardan/Euler angles

A

both provide methods of describing the orientation of rigid body segments in space. Biomechanics uses Cardan

33
Q

Cardan/Euler angle sequencing

A
  1. About an axis in LCS’ (x’y’z’)
  2. About a floating axis (changes according to orientation of 1st and 3rd axis)
  3. about an axis in LCS’’ (x’‘,y’‘,z’’)
34
Q

6 of 12 sequences have terminal axes that are the same as the first rotation axis

A

Euler Angles

35
Q

6 of 12 sequences have terminal axes that are different from the first rotation axes

A

Cardan Angles (actually describe what happend during movement)

36
Q
A

Cardan sequence of rotation xyz

37
Q

Cardan sequence:
Alpha
Beta
Gamma

A

Alpha: Flexion/extension
Beta: add/abduction
Gamma: internal/external rotation

38
Q
A

cardan beta

39
Q
A

cardan alpha

40
Q
A

cardan gamma

41
Q

What does the wand dance do?

A

determines camera and lens variables,
sets x,y,z for all cameras

42
Q

What does static calibration do?

A

-determines origin (absolute reference point only
-depends on successful dynamic calibration

43
Q

What do linear transformations represent?

A

represent P in LCS

44
Q

Where is the singleton origin specified?

45
Q

When is static calibration processed?

46
Q

What does calibration of the GCS require?

A
  1. Geometrical structure with at least 6 points
  2. Dynamic or static calibration

Advanced Biomechanics (7 decks)

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