visual3d:documentation:modeling:segments:constructing_the_segment_coordinate_system
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| visual3d:documentation:modeling:segments:constructing_the_segment_coordinate_system [2024/06/14 17:24] – created sgranger | visual3d:documentation:modeling:segments:constructing_the_segment_coordinate_system [2024/07/17 15:45] (current) – created sgranger | ||
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| - | |**Language: | + | ====== |
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| - | |===== Contents =====\\ \\ \\ \\ * [[# | + | |
| 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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| An alternate version of this tutorial can be found [[Visual3D: | An alternate version of this tutorial can be found [[Visual3D: | ||
| - | ===== Segment Endpoints | + | ==== Segment Endpoints ==== |
| Definition of the proximal or distal end point of a segment is usually done by placing markers near the endpoint of the segment and using one of the following methods. Note that many other methods might be used.\\ | Definition of the proximal or distal end point of a segment is usually done by placing markers near the endpoint of the segment and using one of the following methods. Note that many other methods might be used.\\ | ||
| - | ==== 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) |
| - | ==== Method 2 ==== | + | === Method 2 === |
| If the motion capture markers are not located on the anatomical landmarks because, for example, a lesion or a brace is already at that location, a landmark can be used instead.\\ | If the motion capture markers are not located on the anatomical landmarks because, for example, a lesion or a brace is already at that location, a landmark can be used instead.\\ | ||
| - | | | + | | {{: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 === |
| In some cases it is desirable to use only a lateral marker and an offset.\\ | In some cases it is desirable to use only a lateral marker and an offset.\\ | ||
| - | | | + | | {{: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 ==== |
| The first step in creating a local SCS is the establishment of the frontal plane. Visual3D allows the user to place either one or two border targets at each end of the segment during subject calibration. (The border targets can be of the type MED_DIST, MED_PROX, LAT_DIST and LAT_PROX) Thus the SCS can be created using two targets (a single border target at each end & an extra target to define orientation), | The first step in creating a local SCS is the establishment of the frontal plane. Visual3D allows the user to place either one or two border targets at each end of the segment during subject calibration. (The border targets can be of the type MED_DIST, MED_PROX, LAT_DIST and LAT_PROX) Thus the SCS can be created using two targets (a single border target at each end & an extra target to define orientation), | ||
| - | ==== Figure 1 ==== | + | === Figure 1 === |
| - | |[[File: | + | |{{: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 === |
| - | |[[File: | + | |{{: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 === |
| - | |[[File: | + | |{{: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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| - | ===== Establishing the Segment Ends ===== | + | ==== Establishing the Segment Ends ==== |
| After creating the frontal plane, Visual3D then establishes the distal and proximal segment ends. It should be noted that for kinetic computations, | After creating the frontal plane, Visual3D then establishes the distal and proximal segment ends. It should be noted that for kinetic computations, | ||
| - | ===== Establishing the SCS X, Y and Z Axes ===== | + | ==== Establishing the SCS X, Y and Z Axes ==== |
| The SCS Z axis is determined by the unit vector directed from the distal segment end to the proximal segment end. Next, the SCS Y axis is determined by the unit vector that is perpendicular to both the frontal plane and the Z axis. Finally, the SCS X axis is determined by the application of the right hand rule. From the above discussion it can be seen that, the SCS Z axis is directed from distal to proximal, the SCS Y axis is directed from posterior to anterior, and the SCS X axis is medial-lateral in orientation.\\ | The SCS Z axis is determined by the unit vector directed from the distal segment end to the proximal segment end. Next, the SCS Y axis is determined by the unit vector that is perpendicular to both the frontal plane and the Z axis. Finally, the SCS X axis is determined by the application of the right hand rule. From the above discussion it can be seen that, the SCS Z axis is directed from distal to proximal, the SCS Y axis is directed from posterior to anterior, and the SCS X axis is medial-lateral in orientation.\\ | ||
| - | ==== Establishing the Origin of the SCS ==== | + | === Establishing the Origin of the SCS === |
| The SCS origin is located along the line connecting the segment ends (the SCS Z axis) at the segment' | The SCS origin is located along the line connecting the segment ends (the SCS Z axis) at the segment' | ||
| - | ==== Step-By-Step Procedure | + | === Step-By-Step Procedure === |
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| - | |[[File: | + | |{{: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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| - | |[[File: | + | |{{: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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| - | |[[File: | + | |{{:wireframe3.gif}}|**Step 3.** The frontal plane (x-z) plane is defined by the markers.| |
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| - | |[[File: | + | |{{:wireframe4.gif}}|**Step 4.** The y-axis is project forward in the anterior posterior direction.| |
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| - | |[[File: | + | |{{:wireframe5.gif}}|**Step 5.** The x-axis is then calculated perpendicular to the y-z plane.| |
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| - | [[File: | + | {{:AnnotatedModel.gif}}\\ |
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| - | ===== Modifying the Segment Coordinate System | + | ==== Modifying the Segment Coordinate System ==== |
| There are times in which it is useful to modify the segment coordinate system after the segment has been created. Usually this happens when you want to preserve the segment length from the original construction of the segment, but now need to align the segment coordinate system with another segment coordinate system. [[Visual3D: | There are times in which it is useful to modify the segment coordinate system after the segment has been created. Usually this happens when you want to preserve the segment length from the original construction of the segment, but now need to align the segment coordinate system with another segment coordinate system. [[Visual3D: | ||
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visual3d/documentation/modeling/segments/constructing_the_segment_coordinate_system.1718385866.txt.gz · Last modified: 2024/06/14 17:24 by sgranger