visual3d:documentation:modeling:segments:constructing_the_segment_coordinate_system
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| visual3d:documentation:modeling:segments:constructing_the_segment_coordinate_system [2024/07/03 17:38] – created sgranger | visual3d:documentation:modeling:segments:constructing_the_segment_coordinate_system [2024/07/17 15:45] (current) – created sgranger | ||
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| To measure the motion of anatomical segments, the fixed A for each tracking target must be known. Visual3D uses a static subject calibration trial to establish locally fixed SCSs and subsequently find the fixed A for each tracking target. | To measure the motion of anatomical segments, the fixed A for each tracking target must be known. Visual3D uses a static subject calibration trial to establish locally fixed SCSs and subsequently find the fixed A for each tracking target. | ||
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| === Method 1 === | === Method 1 === | ||
| - | | {{SegmentEndpoint2Targets.gif}}|**Method 1:** The segment endpoint is located at the midpoint between two markers (blue)\\ Segment Endpoint=0.5*Distance(Medial+Lateral) | + | | {{:SegmentEndpoint2Targets.gif}}|**Method 1:** The segment endpoint is located at the midpoint between two markers (blue)\\ Segment Endpoint=0.5*Distance(Medial+Lateral) |
| === Method 2 === | === Method 2 === | ||
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| - | | {{SegmentEndpoint2VirtualTargets.gif}}|**Method 2:** The segment endpoint is located at the midpoint between two landmarks (red) or a combination of one landmark and one marker. The landmarks are defined as offsets (shown as the arrow) from markers. The offsets can be measured on the subject during the data collection or they can be generated from regression equations.\\ Segment End Point= 0.5*Distance(Landmark Medial + Landmark Lateral) | + | | {{:SegmentEndpoint2VirtualTargets.gif}}|**Method 2:** The segment endpoint is located at the midpoint between two landmarks (red) or a combination of one landmark and one marker. The landmarks are defined as offsets (shown as the arrow) from markers. The offsets can be measured on the subject during the data collection or they can be generated from regression equations.\\ Segment End Point= 0.5*Distance(Landmark Medial + Landmark Lateral) |
| === Method 3 === | === Method 3 === | ||
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| - | | {{SegmentEndpoint1Target.gif}}|**Method 3:** The segment endpoint is located at a distance from the lateral marker in the medial direction. The distance is specified in the dialogs as a radius. This is typically used for locating the hip joint center. For example, the lateral marker is placed on the greater trochanter. The location of the hip joint center (the proximal end of the thigh segment) is estimated by palpation. The distance from the greater trochanter to the hip joint center is measured using calipers. | + | | {{:SegmentEndpoint1Target.gif}}|**Method 3:** The segment endpoint is located at a distance from the lateral marker in the medial direction. The distance is specified in the dialogs as a radius. This is typically used for locating the hip joint center. For example, the lateral marker is placed on the greater trochanter. The location of the hip joint center (the proximal end of the thigh segment) is estimated by palpation. The distance from the greater trochanter to the hip joint center is measured using calipers. |
| ==== Establishing an Anatomical Plane ==== | ==== Establishing an Anatomical Plane ==== | ||
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| === Figure 1 === | === Figure 1 === | ||
| - | |{{3Targets.gif}}|**Figure 1.** If three border targets are used then the frontal plane is simply the plane define by the three targets.| | + | |{{:3Targets.gif}}|**Figure 1.** If three border targets are used then the frontal plane is simply the plane define by the three targets.| |
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| === Figure 2 === | === Figure 2 === | ||
| - | |{{4Targets.gif}}|**Figure 2.** If four border targets are used then a leastsquares plane is fit to the four targets. The leastsquares fit is applied such that the sum of squares distance between the targets and the frontal plane is minimized.| | + | |{{:4Targets.gif}}|**Figure 2.** If four border targets are used then a leastsquares plane is fit to the four targets. The leastsquares fit is applied such that the sum of squares distance between the targets and the frontal plane is minimized.| |
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| === Figure 3 === | === Figure 3 === | ||
| - | |{{2Targets.gif}}|**Figure 3.** If only two border targets are used then an extra assumption (constraint) must be supplied. In the two-target case, the frontal plane is defined by the plane containing the two targets and the Visual3D coordinate systems (M3CS) X axis. This is equivalent to assuming that there is no internal-external rotation of the segment with respect to the M3CS.| | + | |{{:2Targets.gif}}|**Figure 3.** If only two border targets are used then an extra assumption (constraint) must be supplied. In the two-target case, the frontal plane is defined by the plane containing the two targets and the Visual3D coordinate systems (M3CS) X axis. This is equivalent to assuming that there is no internal-external rotation of the segment with respect to the M3CS.| |
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| - | |{{wireframe1.gif}}|**Step 1.** The segment endpoints are calculated. As described in the Visual3D documentation elsewhere, there are many ways to calculate the segment endpoint. The relevance to the calculation is that the markers that are used to define the segment endpoints also determine the frontal plane of the segment coordinate system. In this illustration the three red markers are used to calculate the blue segment endpoints| | + | |{{:wireframe1.gif}}|**Step 1.** The segment endpoints are calculated. As described in the Visual3D documentation elsewhere, there are many ways to calculate the segment endpoint. The relevance to the calculation is that the markers that are used to define the segment endpoints also determine the frontal plane of the segment coordinate system. In this illustration the three red markers are used to calculate the blue segment endpoints| |
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| - | |{{wireframe2.gif}}|**Step 2.** The z-axis is defined by the vector from the distal segment endpoint to the proximal segment endpoint.| | + | |{{:wireframe2.gif}}|**Step 2.** The z-axis is defined by the vector from the distal segment endpoint to the proximal segment endpoint.| |
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| - | |{{wireframe3.gif}}|**Step 3.** The frontal plane (x-z) plane is defined by the markers.| | + | |{{:wireframe3.gif}}|**Step 3.** The frontal plane (x-z) plane is defined by the markers.| |
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| - | |{{wireframe4.gif}}|**Step 4.** The y-axis is project forward in the anterior posterior direction.| | + | |{{:wireframe4.gif}}|**Step 4.** The y-axis is project forward in the anterior posterior direction.| |
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| - | |{{wireframe5.gif}}|**Step 5.** The x-axis is then calculated perpendicular to the y-z plane.| | + | |{{:wireframe5.gif}}|**Step 5.** The x-axis is then calculated perpendicular to the y-z plane.| |
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| - | {{AnnotatedModel.gif}}\\ | + | {{:AnnotatedModel.gif}}\\ |
visual3d/documentation/modeling/segments/constructing_the_segment_coordinate_system.1720028316.txt.gz · Last modified: 2024/07/03 17:38 by sgranger