Differences

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--- plug_gait_lower_limb_modified [2025/09/29 19:13] – [Marker Placement Error] wikisysop
+++ plug_gait_lower_limb_modified [2026/02/03 18:26] (current) – wikisysop
@@ Line 10: / Line 10: @@
 //Workstation// or //Nexus// users will be familiar with the Plug-In Gait variation as Vicon's implementation of the CGM.
-In this tutorial, we describe this implementation of [[http://www.vicon.com|Vicon's]] Plug-In Gait using Visual3D, with the necessary modifications made for marker placement error specific to this dataset.
+In this tutorial, we describe this implementation of [[http://www.vicon.com|Vicon's]] Plug-In Gait using Visual3D, with the necessary modifications made for marker placement error specific to this dataset. The original tutorial without modifications can be accessed [[visual3d:tutorials:modeling:plug-in_gait_lower_limb|here]].
 In some trials, clear errors in marker placement can be identified when viewing the model. Here we make the necessary adaptations to the model to compensate.
+A video version of this tutorial can be viewed [[https://youtu.be/MNpJLYX3sz0|here]].
 ====Marker Placement Error====
@@ Line 18: / Line 20: @@
 The placement of markers during static and dynamic trials can significantly impact the accuracy of the data that is captured. In this static trial markers were only placed on the lateral sides of each leg, with some being nearly co-linear and some incorrectly aligned with anatomical features.
-The closer markers are to being placed co-linearly the more difficult it is to define all six degrees of freedom, this can cause error to be amplified leading to an incorrect model.
+The closer markers are to being placed co-linearly the more difficult it is to define all six degrees of freedom, this can make the model more sensitive to noise.
-In this trial, and many others, markers are only placed on the lateral side of each leg. This is done to avoid markers being knocked off during movement trials, however having markers on the lateral and medial side (at least for static trials) helps to improve model accuracy.
+In this trial, like many others, markers are only placed on the lateral side of each leg. This is done to avoid markers being knocked off during movement trials, however having markers on the lateral and medial side (at least for static trials) helps to improve our ability to define segment coordinate systems.
 The placement of the foot markers, especially the heel, in this trial made it challenging to properly define foot positioning. The Toe_Z landmark was added as a solution to this error.
 ====Modifications Explained ====
-**Shank Definition:** In this tutorial the RKNE marker was added as the lateral boundary for the right shank definition. This was added to improve alignment of the shank and correct excessive incorrect internal rotation of the tibia that was previously present.
+**Shank Definition:** In this tutorial the RKNE marker was added as the lateral boundary for the right shank definition. This was added to improve alignment of the shank and correct excessive incorrect internal rotation of the tibia that was previously present. In the original tutorial there was a significant difference in alignment between the shank and thigh segments which is not typically present or anatomically possible, this change in definition was done to correct this error.
-**Toe Landmark:** The R_Toe_Z landmark was introduced to align the anterior axis of the foot with that of the shank and thigh segments (assuming the subject is standing in alignment). It serves as the distal joint center and the posterior foot alignment.
+**Toe Landmark and Definition:** The R_Toe_Z landmark was introduced to align the anterior axis of the foot with that of the shank and thigh segments (assuming the subject is standing in alignment). It serves as the distal joint center and the posterior foot alignment. In the original model the foot was defined by the heel and toe markers, both of which were incorrectly placed causing clear error in foot positioning.
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   - Click **Landmarks** button
   - Click **Add New Landmark** button
-  - Create Landmark: //R_TOE_Z// \\ \\ **Landmark Name:** //R_TOE_Z// \\ **Define Orientation Using:**\\     Click **Starting Point and Existing Segment:** //RTOE and LAB//\\ Offset Using the Following **ML/AP/AXIAL** Offsets:\\    **ML:** //0.0//    **AP:** //0.0//    **AXIAL:** //-0.1// \\ **Check:** //Offset by Percent (1.0 = 100%)//\\ **Do NOT Check:** //Calibration Only Landmark//
+  - Create Landmark: //R_TOE_Z// \\ \\ **Landmark Name:** //R_TOE_Z// \\ **Define Orientation Using:**\\     Click **Starting Point and Existing Segment:** //RTOE and LAB//\\ Offset Using the Following **ML/AP/AXIAL** Offsets:\\    **ML:** //0.0//    **AP:** //0.0//    **AXIAL:** //-0.1// \\ **Do Not Check:** //Offset by Percent (1.0 = 100%)//\\ **Check:** //Calibration Only Landmark//
@@ Line 226: / Line 229: @@
 The images below show the original model, before modifications, compared to the modified model. Significant errors in tibial rotation and foot orientation can be seen in the original that are corrected for in the updated model.
-Original:
+**Original:**
 {{:without_mods.png?400|}}
-Modified:
+**Modified:**
 {{:with_mods.png?400|}}
+As a result of the modifications made in this tutorial the updated model shows improved alignment between the thigh, shank, and foot segments as well as a more neutral (less supinated) foot position.