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visual3d:documentation:modeling:landmarks:landmark_types [2024/06/19 13:57] – created sgrangervisual3d:documentation:modeling:landmarks:landmark_types [2024/07/17 15:45] (current) – created sgranger
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 +====== Landmark Types ======
 +
 Landmarks provide a powerful method of representing significant locations within space or locations defined by the model. Landmarks are created by either specifying a location in a segment coordinate system or by transforming markers or other landmarks into a significant location. Landmarks provide a powerful method of representing significant locations within space or locations defined by the model. Landmarks are created by either specifying a location in a segment coordinate system or by transforming markers or other landmarks into a significant location.
  
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 The landmark mechanism is the key to Visual3D’s highly flexible modeling capabilities. A single example suffices to suggest the usefulness of markers. Frequently, target markers are mounted on short posts which protrude away from the skin surface, and consequently, defining a segment using medial and lateral markers as described above will tend to over-estimate the segment’s radii. You can eliminate this problem by creating landmarks which are like "shadow versions" of the actual markers, moved inward by the length of the marker posts to better approximate the skin surface, and then define your segments based on these landmarks. The landmark mechanism is the key to Visual3D’s highly flexible modeling capabilities. A single example suffices to suggest the usefulness of markers. Frequently, target markers are mounted on short posts which protrude away from the skin surface, and consequently, defining a segment using medial and lateral markers as described above will tend to over-estimate the segment’s radii. You can eliminate this problem by creating landmarks which are like "shadow versions" of the actual markers, moved inward by the length of the marker posts to better approximate the skin surface, and then define your segments based on these landmarks.
  
-===== Pipeline Commands =====+==== Pipeline Commands ====
  
 If you want to [[Visual3D:Documentation:Pipeline:Model_Commands:Modeling_Commands#Add_Landmark|create a landmark using a pipeline command]] and you already know how to create the landmark interactively in Model Builder Mode, you can save the model template to disk. Open the model template and search for the Landmark definition. You can then cut-and-paste the definition into a pipeline. The only difference will be that you must specify the Model that is to be used; e.g. the model template already defines which model is to be used to create the landmark. If you want to [[Visual3D:Documentation:Pipeline:Model_Commands:Modeling_Commands#Add_Landmark|create a landmark using a pipeline command]] and you already know how to create the landmark interactively in Model Builder Mode, you can save the model template to disk. Open the model template and search for the Landmark definition. You can then cut-and-paste the definition into a pipeline. The only difference will be that you must specify the Model that is to be used; e.g. the model template already defines which model is to be used to create the landmark.
  
-===== Landmark Extent =====+==== Landmark Extent ====
  
 Landmarks can be 'calibration only' or can be calculated for the motion files. Landmarks can be 'calibration only' or can be calculated for the motion files.
  
-==== Calibration Only ====+=== Calibration Only ===
  
 Used only for segment calibration, but are not needed (or produced) for any associated motion file(s). Used only for segment calibration, but are not needed (or produced) for any associated motion file(s).
  
-==== Generated for Assigned Motion Files ====+=== Generated for Assigned Motion Files ===
  
 Generated for the calibration file, and the associated motion files. These landmarks may be used for tracking a segment. Generated for the calibration file, and the associated motion files. These landmarks may be used for tracking a segment.
  
-===== Landmark Types =====+==== Landmark Types ====
  
 There are several landmark types or ways to create landmarks. Landmarks can be created: There are several landmark types or ways to create landmarks. Landmarks can be created:
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   - to create muscles which are defined by linear segments connecting a series of Landmarks.   - to create muscles which are defined by linear segments connecting a series of Landmarks.
  
-==== Point Projected on a line ====+=== Point Projected on a line ===
  
 Point projection onto a line can be used at the shoulder to project a lateral target on to a vertical line passing through the acromium or it can be used at the knee to project lateral or medial targets on a functional axis. Point projection onto a line can be used at the shoulder to project a lateral target on to a vertical line passing through the acromium or it can be used at the knee to project lateral or medial targets on a functional axis.
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 In the image below, the **RAnkleCenter** is the point that is created by projecting the **RHL** heel marker onto the line created from the lateral and medial ankle markers **RLA** and **RMA**. In the image below, the **RAnkleCenter** is the point that is created by projecting the **RHL** heel marker onto the line created from the lateral and medial ankle markers **RLA** and **RMA**.
  
-{{landmark_point_projected_onto_a_line.jpg}}+{{:landmark_point_projected_onto_a_line.jpg}}
  
 Another example can be found on this page, [[Visual3D:Documentation:Modeling:Landmarks:Projecting_a_marker_onto_a_line|Project onto a line]]. Another example can be found on this page, [[Visual3D:Documentation:Modeling:Landmarks:Projecting_a_marker_onto_a_line|Project onto a line]].
  
-==== Point Projected on to a plane ====+=== Point Projected on to a plane ===
  
 By projecting multiple landmarks onto the same plane you can build segment coordinates systems in a specific plane. To define a landmark as a point projected onto a plane defined by 3 points, select the Targets and/or Landmarks radio button. Select three targets and/or landmarks for the Reference/Axial Starting Point, Axial Ending Point and Lateral object to define a plane. Select a point to project using the Projected From combo box. By projecting multiple landmarks onto the same plane you can build segment coordinates systems in a specific plane. To define a landmark as a point projected onto a plane defined by 3 points, select the Targets and/or Landmarks radio button. Select three targets and/or landmarks for the Reference/Axial Starting Point, Axial Ending Point and Lateral object to define a plane. Select a point to project using the Projected From combo box.
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 In the image below, the **RPPinPlane** is the point that is created by projecting the **RPP** marker on the illiac crest onto the plane created from the right and left ASIS's (**RASI**,**LASI**) and the right PSIS **RPS** marker. In the image below, the **RPPinPlane** is the point that is created by projecting the **RPP** marker on the illiac crest onto the plane created from the right and left ASIS's (**RASI**,**LASI**) and the right PSIS **RPS** marker.
  
-{{landmark_point_projected_onto_a_plane.jpg}}+{{:landmark_point_projected_onto_a_plane.jpg}}
  
-=== Example 1: Project the hip joint onto a plane passing through the GT's ===+== Example 1: Project the hip joint onto a plane passing through the GT's ==
  
 This example will illustrate how one would project a hip joint center landmark onto frontal plane of the pelvis passing through the greater trochanters. This example will illustrate how one would project a hip joint center landmark onto frontal plane of the pelvis passing through the greater trochanters.
  
-=== Example 2: Project onto a principal plane ===+== Example 2: Project onto a principal plane ==
  
 This is an example of how one would project a heel marker, RHEEL on the floor or X-Y plane of the laboratory. This is an example of how one would project a heel marker, RHEEL on the floor or X-Y plane of the laboratory.
  
-==== Offsets ====+=== Offsets ===
  
 Landmarks are often offsets from existing target markers. The origin of the offset is the starting point (reference point). The offset is specified as an absolute distance in meters, or as a percentage. The percentage is relative to a segment or markers. Landmarks are often offsets from existing target markers. The origin of the offset is the starting point (reference point). The offset is specified as an absolute distance in meters, or as a percentage. The percentage is relative to a segment or markers.
  
-=== Use regression equations as offset ===+== Use regression equations as offset ==
  
 One can use regression equations as an offset in the landmark definition (i.e. Hip joint centers) see the example in the previous section [[Visual3D:Documentation:Modeling:Landmarks:Projecting_a_marker_onto_a_plane|Example 1: Project the hip joint onto a plane passing through the GT's]]. One can use regression equations as an offset in the landmark definition (i.e. Hip joint centers) see the example in the previous section [[Visual3D:Documentation:Modeling:Landmarks:Projecting_a_marker_onto_a_plane|Example 1: Project the hip joint onto a plane passing through the GT's]].
  
-== Hip Landmark ==+= Hip Landmark =
  
 Landmarks defining the location of the hip joint center are not particularly notable except that two of the default Pelvis segment types (Coda and Helen Hayes) create hip joint landmarks automatically when the segment is created. Landmarks defining the location of the hip joint center are not particularly notable except that two of the default Pelvis segment types (Coda and Helen Hayes) create hip joint landmarks automatically when the segment is created.
  
-== Bell and Brand Hip ==+= Bell and Brand Hip =
  
 Specifying the Hip Joint Landmark using Bell and Brand. This page will also illustrate how to create a generic pelvis technical coordinate system and hip landmarks. Specifying the Hip Joint Landmark using Bell and Brand. This page will also illustrate how to create a generic pelvis technical coordinate system and hip landmarks.
  
-== Hip Landmark from Custom Regression Equation ==+= Hip Landmark from Custom Regression Equation =
  
 Specifying the Hip Joint Landmark using a custom regression equation Specifying the Hip Joint Landmark using a custom regression equation
  
-=== Relative to a segment ===+== Relative to a segment ==
  
 Landmarks can be created relative to a segment (in the segment coordinate system). Landmarks can be created relative to a segment (in the segment coordinate system).
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 If you would like to offset the landmark in lab space, you may select the **LAB** segment in the existing segment combo box. When the landmark is relative to the **LAB** the offsets are the X, Y and Z directions of the lab. If you would like to offset the landmark in lab space, you may select the **LAB** segment in the existing segment combo box. When the landmark is relative to the **LAB** the offsets are the X, Y and Z directions of the lab.
  
-== Landmark relative to a thigh segment ==+= Landmark relative to a thigh segment =
  
 This is an example of creating a landmark relative to a thigh segment with ML, AP, and AXIAL offsets in percent. This is an example of creating a landmark relative to a thigh segment with ML, AP, and AXIAL offsets in percent.
  
-== Landmark at segment endpoint ==+= Landmark at segment endpoint =
  
 Creating a landmark at the end of a segment that is tracked with the segment Creating a landmark at the end of a segment that is tracked with the segment
  
-== Example using a reference location ==+= Example using a reference location =
  
 This example creates a landmark relative to a segment (or to 3 markers) using a reference location. This example creates a landmark relative to a segment (or to 3 markers) using a reference location.
  
-==== Relative to 3 Locations ====+=== Relative to 3 Locations ===
  
 Landmarks can be created relative to 3 locations. This can be handy when removing markers in the motion trials. Landmarks can be created relative to 3 locations. This can be handy when removing markers in the motion trials.
  
-{{landmark3a.jpg}}+{{:landmark3a.jpg}}
  
-{{landmark3b.jpg}}+{{:landmark3b.jpg}}
  
 A right handed orthogonal coordinate system is defined by the three points (P1, P2, P3). A right handed orthogonal coordinate system is defined by the three points (P1, P2, P3).
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-=== Landmark Type 5 ===+== Landmark Type 5 ==
  
 Create a landmark defining the location of a segment endpoint relative to 3 tracking markers (or landmarks). Create a landmark defining the location of a segment endpoint relative to 3 tracking markers (or landmarks).
  
-==== Digitized Landmarks ====+=== Digitized Landmarks ===
  
 The objective for using the pointer is to identify anatomical landmarks without having to place motion capture markers at the location. The objective for using the pointer is to identify anatomical landmarks without having to place motion capture markers at the location.
  
-==== Functional Landmarks (Joints) ====+=== Functional Landmarks (Joints) ===
  
 The functional joint calculations have been adapted from: The functional joint calculations have been adapted from:
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 and from and from
 [[[http://www.sciencedirect.com/science/article/pii/S0021929016303979|Jensen E, Lugade V, Crenshaw J, Miller E, Kaufman K (2016) A principal component analysis approach to correcting the knee flexion axis during gait. Journal of Biomechanics, in press]]] [[[http://www.sciencedirect.com/science/article/pii/S0021929016303979|Jensen E, Lugade V, Crenshaw J, Miller E, Kaufman K (2016) A principal component analysis approach to correcting the knee flexion axis during gait. Journal of Biomechanics, in press]]]
-==== Muscles ====+=== Muscles ===
  
 Muscles are defined by linear segments connecting a series of Landmarks. The Landmarks can be created using any of the rules for creating landmarks in Visual3D. Muscles are defined by linear segments connecting a series of Landmarks. The Landmarks can be created using any of the rules for creating landmarks in Visual3D.
  
-===== Examples =====+==== Examples ====
  
-==== Create a Landmark Mimicking contralateral segment ====+=== Create a Landmark Mimicking contralateral segment ===
  
 It was not possible to place anatomical landmarks on the medial and lateral ankle of the subject because the subject was missing one lower limb. It was possible to place markers on the foot prosthesis consistent with the existing foot. Assuming symmetry in the two foot segments the user wanted to create landmarks representing the location of the medial and lateral ankle of the missing shank relative to the foot coordinate system consistent with the location of the medial and lateral ankle in the existing segment. It was not possible to place anatomical landmarks on the medial and lateral ankle of the subject because the subject was missing one lower limb. It was possible to place markers on the foot prosthesis consistent with the existing foot. Assuming symmetry in the two foot segments the user wanted to create landmarks representing the location of the medial and lateral ankle of the missing shank relative to the foot coordinate system consistent with the location of the medial and lateral ankle in the existing segment.
-==== Create Landmarks from a Knee Alignment Device ====+=== Create Landmarks from a Knee Alignment Device ===
  
 The [[Visual3D:Documentation:Modeling:Segments:Knee_Alignment_Device|Knee Alignment Device]] (KAD) is manufactured by Motion Lab Systems. The KAD is used to assist in defining the frontal plane of the thigh segment. This page describes the KAD and shows how it is implemented to create the frontal plane and landmarks in Visual3D. The [[Visual3D:Documentation:Modeling:Segments:Knee_Alignment_Device|Knee Alignment Device]] (KAD) is manufactured by Motion Lab Systems. The KAD is used to assist in defining the frontal plane of the thigh segment. This page describes the KAD and shows how it is implemented to create the frontal plane and landmarks in Visual3D.
  
-==== Create a Landmark Using two standing trials ====+=== Create a Landmark Using two standing trials ===
  
 Landmarks can be created from two static standing trials. Landmarks can be created from two static standing trials.
  
-=== Replacing missing landmark ===+== Replacing missing landmark ==
  
 We collected 2 sets of studies for the same person, and we collected one static trial of the lower extremity for each set of the study. We forgot to add the GT markers for the first static trial. Based on what we have right now (a complete 2nd static trial and the 1st static trial with GT markers missing), is it possible for us to create a virtual GT marker for the first static trial? We collected 2 sets of studies for the same person, and we collected one static trial of the lower extremity for each set of the study. We forgot to add the GT markers for the first static trial. Based on what we have right now (a complete 2nd static trial and the 1st static trial with GT markers missing), is it possible for us to create a virtual GT marker for the first static trial?
  
-==== Create a Landmark for a Missing Tracking Marker ====+=== Create a Landmark for a Missing Tracking Marker ===
  
 Landmarks can be created to calculate missing tracking markers. Landmarks can be created to calculate missing tracking markers.
  
-=== Example: Missing Tracking Marker in Static Trial ===+== Example: Missing Tracking Marker in Static Trial ==
  
 Consider the following right thigh segment constructed using static markers RPPT, RAPT, RPDT, RADT. These tracking markers are saved to a model template, but for the next subject the static trial is missing the RAPT marker. A landmark can be created to replace the missing tracking marker. Consider the following right thigh segment constructed using static markers RPPT, RAPT, RPDT, RADT. These tracking markers are saved to a model template, but for the next subject the static trial is missing the RAPT marker. A landmark can be created to replace the missing tracking marker.
  
-==== Create Landmarks from Motion Trial ====+=== Create Landmarks from Motion Trial ===
  
 Landmarks can be created from the motion trials. Landmarks can be created from the motion trials.
  
-=== Using Motion Trial Example 1 ===+== Using Motion Trial Example 1 ==
  
 This example creates landmarks from Targets in a movement trial but not in the standing trial. In this example, a movement trial contains 4 markers that have been placed on the corners of an object. The standing trial does not contain these markers, but needs the corner locations for defining an object (segment). This example creates landmarks from Targets in a movement trial but not in the standing trial. In this example, a movement trial contains 4 markers that have been placed on the corners of an object. The standing trial does not contain these markers, but needs the corner locations for defining an object (segment).
  
-=== Using Motion Trial Example2 ===+== Using Motion Trial Example2 ==
  
 A structure (i.e. stairs) can be defined by placing markers at vertices, then connecting these vertices. It isn't always practical, however, to place these markers during the standing trial, so it would be useful to have a separate motion trial that contained only these markers. In this example, we demonstrate how to get the marker locations from a movement trial and create landmarks. In the movement trial for this example, markers are placed on the steps of a set of stairs. A structure (i.e. stairs) can be defined by placing markers at vertices, then connecting these vertices. It isn't always practical, however, to place these markers during the standing trial, so it would be useful to have a separate motion trial that contained only these markers. In this example, we demonstrate how to get the marker locations from a movement trial and create landmarks. In the movement trial for this example, markers are placed on the steps of a set of stairs.
visual3d/documentation/modeling/landmarks/landmark_types.1718805464.txt.gz · Last modified: 2024/06/19 13:57 by sgranger