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--- visual3d:documentation:marker_based_motion_capture [2026/05/26 19:44] – wikisysop
+++ visual3d:documentation:marker_based_motion_capture [2026/06/09 13:26] (current) – wikisysop
@@ Line 1: / Line 1: @@
-====== Marker-Based Motion Capture Overview (Under Construction) ======
+====== Marker-Based Motion Capture Overview ======
+Marker-based motion capture systems can be split into passive and active systems.
+**Passive marker-based systems** generally use retroreflective markers placed on the body in accordance with a particular marker set. Cameras are set up to record the near infrared light reflected by these markers and estimate the 3-dimensional position of these markers throughout the movement. A model, essentially a mapping from markers to the skeleton, provides these marker positions with biomechanical meaning and is defined by the user. This model is applied to the recorded 3D marker positions during dynamic movements of interest to produce pose estimates.
+**Active marker-based systems** generally use markers that emit light, which are placed on the body. Cameras record the light emitted by these markers and estimate their 3-dimensional position throughout the movement.
 ===== Marker Sets =====
-Before data collection using markerbased motion capture, you should decide on the appropriate [[visual3d:documentation:modeling:marker_sets:marker_sets_overview|Marker Set]] for your research question. See the [[visual3d:documentation:modeling:marker_sets:marker_set_guidelines|Marker Set Guidelines]] and read more on [[visual3d:documentation:modeling:marker_sets:marker_placement|Marker Placement]].
+Before data collection using marker-based motion capture, you should decide on the appropriate [[visual3d:documentation:modeling:marker_sets:marker_sets_overview|Marker Set]] for your research question. See the [[visual3d:documentation:modeling:marker_sets:marker_set_guidelines|Marker Set Guidelines]] and read more on the specific considerations of [[visual3d:documentation:modeling:marker_sets:marker_placement|Marker Placement]].
 In general, the marker set will comprise of:
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 // Fig. 1. Visual of anatomical and tracking markers on a left tibia. The segment coordinate system is defined at the proximal end of the segment //
+Marker sets commonly fall into three families:
+  - Plug-in Gait ([[visual3d:documentation:modeling:marker_sets:pig_ll_original|Plug-in Gait Original Marker Set]], [[visual3d:documentation:modeling:marker_sets:plug-in_gait_clavicle|Plug-in Gait Clavicle Marker Set]], [[visual3d:tutorials:modeling:plug-in_gait_lower_limb|Plug-in Gait Lower Limb]])
+  - IOR Gait ([[other:ior_gait:ior_gait_overview|IOR Gait Overview]])
+  - OptiTrack ([[visual3d:documentation:modeling:marker_sets:optitrack_biomech_57_marker_set|OptiTrack Biomech 57 Marker Set]])
-Some common marker sets include:
-  * The [[visual3d:documentation:modeling:marker_sets:optitrack_biomech_57_marker_set|OptiTrack Biomech 57 Marker Set]]
-  * The [[visual3d:documentation:modeling:marker_sets:pig_ll_original|Plug-in Gait Original Marker Set]]
-  * The [[visual3d:documentation:modeling:marker_sets:plug-in_gait_clavicle|Plug-in Gait Clavicle Marker Set]]
-  * The [[visual3d:tutorials:modeling:ior_gait_full_body_model|IOR Gait Full Body Model]]
 ===== Data Collection =====
-A [[visual3d:documentation:definitions:static_trial|static trial]] of the subject is required to define the segment coordinate system and build the model. The position of the subject will depend on the marker set you selected (e.g. T-pose). Subsequent Dynamic Trials should contain the movement of interest to be analyzed.
+A [[visual3d:documentation:definitions:static_trial|static trial]] of the subject is required to define the segment coordinate system and build the model. The position of the subject will depend on the marker set you selected and the activity you want to look at. Subsequent Dynamic Trials should contain the movement of interest to be analyzed.
 ===== Model Building =====
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 To visualize your motion data, check out the [[visual3d:tutorials:reports:visualizing_data|Visualizing Data]] tutorial.
-===== In Addition to Marker-Based MOCAP =====
-==== Forces ====
-If you collected force data along with your markerbased data, you can [[visual3d:documentation:kinematics_and_kinetics:external_forces:force_assignment|assign those forces]] to the model that you built in Visual3D and compute [[visual3d:documentation:kinematics_and_kinetics:inverse_dynamics|Inverse Dynamics]]. See the [[visual3d:documentation:kinematics_and_kinetics:external_forces:force_overview|Force Overview]] page.
-==== EMG ====
-Another method of biomechanical data collection is [[visual3d:documentation:emg:emg_overview|electromyography (EMG)]], which may be collected synchronously with markerbased data.