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visual3d:documentation:modeling:segments:pelvis_overview [2024/06/19 13:58] – created sgrangervisual3d:documentation:modeling:segments:pelvis_overview [2026/06/09 21:29] (current) – Restricted focus to this page being an overview page. wikisysop
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 +====== Pelvis Overview ======
 +
 There are many ways to define a segment in Visual3D, which means there are many ways to define a Pelvis segment. There are many ways to define a segment in Visual3D, which means there are many ways to define a Pelvis segment.
  
-A pelvis segment can be constructed as any other segment, and so the default pelvis segment in Visual3D is labeled a [[Visual3D:Documentation:Modeling:Segments:Visual3D_Pelvis|Visual3D Pelvis]]. Visual3D inherited this definition from [[Visual3D:References|MOVE3D]] (the precursor software to Visual3D) and has been used by the staff in the Physical Disabilities Branch at the NIH for more than 20 years. +^ Model Name ^ Description ^ 
- +| [[visual3d:documentation:modeling:segments:visual3d_pelvis|Visual3D Pelvis]] | The Visual3D pelvis refers to a pelvis segment defined as a default Visual3D segments. Markers on the Iliac Crest specify the proximal end of the segment. Markers on the Greater Trochanter specify the distal end of the segment. The length of the Pelvis segment is defined as the distance from the proximal end to the distal end. Visual3D inherited this definition from [[Visual3D:References|MOVE3D]] (the precursor software to Visual3D) and has been used by the staff in the Physical Disabilities Branch at the NIH for more than 20 years.| 
-Visual3D has two other Pelvis types in Visual3D that share the same resultant segment coordinate system, but each has associated regression equations that define the location of the Hip Joint Centers (defined in the Pelvis segment coordinate system). +| [[visual3d:documentation:modeling:segments:coda_pelvis|CODA Pelvis]] | The CODA pelvis refers to a pelvis segment model used by Charnwood Dynamics that they requested that we implement. The pelvis segment is defined using the anatomical locations of the ASIS (Anterior Superior Iliac Spine) and the PSIS (Posterior Superior Iliac Spine). These landmarks are bony protuberances on the Pelvis bones that can be palpated on most (but not all) subjects.| 
- +| [[visual3d:documentation:modeling:segments:helen_hayes_davis_pelvis|Helen Hayes (Davis) Pelvis]] | The Helen Hayes pelvis refers to a model defined by Davis et. at. (1991) and used by many manufacturers, including the VCM model by Vicon. The pelvis segment is defined using the anatomical locations of the ASIS (Anterior Superior Iliac Spine) and the midpoint between the PSIS (Posterior Superior Iliac Spine) commonly referred to as the Sacrum marker. These landmarks are bony protuberances on the Pelvis bones that can be palpated on most (but not all) subjects. | 
-[[Visual3D:Documentation:Modeling:Segments:Coda_Pelvis|Coda_Pelvis]] +| [[visual3d:documentation:modeling:segments:v3d_composite_pelvis|Visual3D Composite Pelvis]] | The Visual3D Composite Pelvis has a local coordinate system that is aligned with many of the traditional pelvis definitions (CODA, Helen Hayes, Plugin-Gait), but the origin of the segment is in the middle of the body, which is more representative of the inertial properties. |
- +
-[[Visual3D:Documentation:Modeling:Segments:Helen_Hayes_(Davis)_Pelvis|Helen Hayes (Davis) Pelvis]] +
- +
-===== Choosing between Helen Hayes and CODA Pelvis ===== +
- +
-I usually recommend choosing the CODA Pelvis within Visual3D mostly because it does not require an estimate of the Leg Length, which can be a bit of a problem for some patients. The CODA pelvis also does not require the measurement of the ASIS-greater trochanter distance, which I find that very few laboratories ever make.\\ +
- +
- +
-\\ +
-**For the CODA/DAVIS pelvis the segment coordinate system typically will be tilted forward about 20 degrees forward. It is possible, however, to create a Visual3D pelvis from this same data set such that the pelvic tilt matches the clinical measure of pelvic tilt.**\\ +
- +
- +
-===== Creating Visual3D Pelvis from Coda Pelvis ===== +
- +
-The Visual3D pelvis is created typically using Iliac Crest markers and Greater Trochanter markers. The Conventional Gait marker set, however, does not include these markers. One of the consequences of creating a CODA/DAVIS pelvis, however, is that Hip Joint Centers are created automatically based on regression equations. +
- +
-The following process can be used to create a Visual3D pelvis segment coordinate system using the Conventional Gait marker set. +
- +
-First, create a CODA pelvis and note the creation of **Hip Joint** Landmarks.\\ +
- +
- +
-|{{normalizedPelvis1.gif}}     |{{normalizedPelvis2.gif}}| +
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-\\ +
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-Remove the animation model associated with the CODA pelvis. Switch to the Segment Properties tab and remove the assignment to the obj and col files.\\ +
- +
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-{{normalizedPelvis3.gif}}\\ +
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- +
-Create landmarks to represent the location of the Iliac Crest markers. In this example, I elected to have a segment coordinate system aligned with the laboratory, resulting in a pelvic tilt of zero degrees. Modifying the location of the landmarks will allow the creation of any orientation.\\ +
- +
- +
-|{{normalizedPelvis4.gif}}     |{{normalizedPelvis5.gif}}| +
- +
-\\ +
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-Create the Visual3D Pelvis\\ +
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- +
-{{normalizedPelvis6.gif}}\\ +
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-Note the difference in orientation of the two pelvis segment coordinate systems.\\ +
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-\\ +
  
-The previous process created a pelvis segment coordinate system that was aligned vertically by creating landmarks located vertically above the hip joint centers. Any pelvic tile, however, can be created by a modest change to the landmark definitions.+**NOTE**: the segment coordinate system for the CODA pelvis is the mid-point between the ASIS markers. The anatomical landmarks are actually posterior to the ASIS markers because the motion capture system tracks the center of the marker. This is a modest error, but it can be corrected by [[visual3d:documentation:modeling:segments:create_coda_pelvis_relative_to_anatomical_landmarks|creating landmarks that are posterior to the ASIS markers by the radius of the motion capture marker]].
  
-**Note:** Visual3D allows the use of mathematical expressions in most of the edit boxes in model builder model. In the previous section the following landmarks were created.\\+===== Choosing between Helen Hayes and CODA Pelvis Approaches =====
  
 +We usually recommend choosing the CODA Pelvis family within Visual3D. This is mostly because these definitions do not require an estimate of the Leg Length, which can be a bit of a problem for some patients. The CODA pelvis also does not require the measurement of the ASIS-greater trochanter distance, which we find that very few laboratories ever make.
  
-**Landmark Name=**Right Iliac Crest +===== Pelvis Segment Angle =====
-**Starting Point=**RIGHT_HIP +
-Offset Using the Following ML/AP/AXIAL Offsets= Checked +
-**X=**0.0 +
-**Y=**0.0 +
-**Z=**0.19 +
-**Landmark Name=**Left Iliac Crest +
-**Starting Point=**LEFT_HIP +
-**Offset Using the Following ML/AP/AXIAL Offsets=** Checked +
-**X=**0.0 +
-**Y=**0.0 +
-**Z=**0.19 +
-Assuming the y-direction is Anterior. We can create a forward tilt of the pelvis of 0.3 radians by modifying the landmarks as follows:\\+
  
 +The Pelvis Angle typically refers to the orientation of the Pelvis relative to the Laboratory. In Richard Baker's 2001 technical note((Baker R (2001) Pelvic angles: a mathematically rigorous definition which is consistent with a conventional clinical understanding of the terms. Gait and Posutre 13, 1-6)) he makes a convincing (to us anyway) claim that the sequence of rotations for the Cardan angle description of the pelvis relative to the laboratory should be:
 +  - Axial Rotation
 +  - Obliquity
 +  - Tilt.
  
-**Landmark Name=**Right Iliac Crest +This is the reverse rotation sequence of the conventional Joint Coordinate System definition of a joint angle commonly used to describe the angles of the hip, knee and ankle, which is Flexion/Extension, Abduction/Adduction, Axial Rotation. This recommendation is easily accomplished in Visual3D by following [[visual3d:documentation:modeling:segments:pelvis_segment_angle|these examples]].
-**Starting Point=**RIGHT_HIP +
-**Offset Using the Following ML/AP/AXIAL Offsets=** Checked +
-**X=**0.0 +
-**Y=**0.19*sin(0.3) +
-**Z=**0.19*cos(0.3) +
-**Landmark Name=**Left Iliac Crest +
-**Starting Point=**LEFT_HIP +
-**Offset Using the Following ML/AP/AXIAL Offsets=** Checked +
-**X=**0.0 +
-**Y=**0.19*sin(0.3) +
-**Z=**0.19*cos(0.3)+
  
  
visual3d/documentation/modeling/segments/pelvis_overview.1718805492.txt.gz · Last modified: by sgranger