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--- visual3d:documentation:pipeline:force_commands:fp_corners [2024/06/17 18:19] – created sgranger
+++ visual3d:documentation:pipeline:force_commands:fp_corners [2025/01/16 18:26] (current) – Clean up page. wikisysop
@@ Line 1: / Line 1: @@
+===== FP CORNERS =====
+This page provides an overview of the [[visual3d:documentation:c3d_signal_types:c3d_format#c3d_parameter_format|C3D Parameter]] FORCE_PLATFORM:CORNERS. This parameter provides information about the location of a force platform's corners, which allows the measurements recorded by this platform to be integrated with other motion capture data.
+The force platform's corners are numbered from 1 to 4 with the coordinates for each corner specified in the [[visual3d:documentation:definitions:laboratory_coordinate_system|Laboratory Coordinate System]] in units consistent with the [[visual3d:documentation:c3d_signal_types:target_data_type|POINT data]]. The order is specified by the quadrant numbers in the force platform coordinate system:
+  - (+x,+y)
+  - (-x, +y)
+  - (-x, -y)
+  - ( +x, -y).
+Visual3D uses these force platform corners to calculate the transformation matrix from the force platform's coordinate system to the laboratory coordinate system. This transformation matrix is then used to transform the force vector from the force platform coordinate system (in which it was collected) into the laboratory coordinate system where it is used for the analysis.
-C3D Parameter FORCE_PLATFORM:CORNERS
+The Force Platform corners can be modified using the [[Visual3D:Documentation:Pipeline:Force_Commands:Modify_Force_Platform_Parameters|Modify_Force_Platform_Parameters]] selection under the Visual3D File Menu
-The force platform corners are numbered from 1 to 4. The values are specified in the Laboratory Coordinate System in units consistent with the POINT data. The order is specified by the quadrant numbers in the force platform coordinate system.
+==== Transforming the Ground Reaction Force into the Laboratory Coordinate System ====
-The order is (+x,+y), (-x, +y), (-x, -y), ( +x, -y).
+The following pseudo-code describes the algorithm for computing the transformation from the Force Platform Coordinate System (FPCS) to the Laboratory Coordinate System (LCS)
-Visual3D calculates the transformation matrix from the force platform coordinate system to the laboratory coordinate system using the force platform corners. This transformation matrix is then used to transform the force vector from the force platform coordinate system (in which it was collected) into the laboratory coordinate system where it is used for the analysis.
+<code>
+ x_vector = unit_vector(corner3 - corner2)
+ y_vector = unit_vector(corner1 - corner2)
+ z_vector = cross_product(x_vector , y_vector)
+ y_vector = cross_product(z_vector , x_vector)
-The Force Platform corners can be modified using the [[Visual3D:Documentation:Pipeline:Force_Commands:Modify_Force_Platform_Parameters|Modify_Force_Platform_Parameters]] selection under the Visual3D File Menu
-===== Transforming the Ground Reaction Force into the Laboratory Coordinate System =====
+Rotation Matrix - FPCS to LCS
+ fpcs_to_lcs column1= x_vector
+ fpcs_to_lcs column2= y_vector
+ fpcs_to_lcs column3= z_vector
-The following pseudo-code describes the algorithm for computing the transformation from the Force Platform Coordinate System (FPCS) to the Laboratory Coordinate System (LCS)
-x_vector = unit_vector(corner3 - corner2)
-y_vector = unit_vector(corner1 - corner2)
-z_vector = cross_product(x_vector , y_vector)
-y_vector = cross_product(z_vector , x_vector)
-Rotation Matrix - FPCS to LCS
-fpcs_to_lcs column1= x_vector
-fpcs_to_lcs column2= y_vector
-fpcs_to_lcs column3= z_vector
 location of top center of force platform in LCS
 platform_top_center_lcs= average(corner1, corner2, corner3, corner4)
 vector from plate origin to top center relative to lab
 Rotate_to_Lab(forceplatform_origin)
 vector from LCS origin to platform origin
 platform_origin_lcs= platform_top_center_lcs- vector from plate origin to top center
-===== Example_1 Using mocap markers to define the corners =====
+</code>
+==== Example 1: Use average marker locations to define force platform corners ====
 Consider the following markers to be placed on the corners of a force platform.
+  * FP1_1
+  * FP1_2
+  * FP1_3
+  * FP1_4
-FP1_1, FP1_2, FP1_3, FP1_4
+Capture a short trial of these markers and create the following pipeline:
-Capture a short trial of these markers.
-Create the following pipeline:
+<code>
 !First define the marker radius as a pipeline parameter
-\\
+Set_Pipeline_Parameter
-[[Visual3D:Documentation:Pipeline:Pipeline_Commands:Set_Pipeline_Parameter|Set_Pipeline_Parameter]]
 /PARAMETER_NAME=MARKER_RADIUS
 /PARAMETER_VALUE=10
-**;**
+;
-\\
 ! Compute the median value of the corners over all frames of the trial.
 ! the result will be placed in the Global Workspace
-\\
+Metric_Median
-[[Visual3D:Documentation:Pipeline:Metric_Commands:Metric_Median|Metric_Median]]
 /RESULT_METRIC_NAME=_MED
 /APPLY_AS_SUFFIX_TO_SIGNAL_NAME=TRUE
@@ Line 68: / Line 70: @@
 ! /GENERATE_MEAN_AND_STDDEV=TRUE
 ! /APPEND_TO_EXISTING_VALUES=FALSE
-\\
+;
 ! If the force platform parameters have already been defined, we only need to modify the corners.
 ! Note that the markers are in meters, but the following command requires millimeters
-\\
+Modify_Force_Platform_Parameters
-[[Visual3D:Documentation:Pipeline:Force_Commands:Modify_Force_Platform_Parameters|Modify_Force_Platform_Parameters]]
 /FP_USED=1
 /FP_CORNER1= 1000*GLOBAL::METRIC::FPLOC::FP1_1_MED_MEAN::X
@@ Line 90: / Line 88: @@
 +1000*GLOBAL::METRIC::FPLOC::FP1_4_MED_MEAN::Y
 +1000*(GLOBAL::METRIC::FPLOC::FP1_4_MED_MEAN::Z-&::MARKER_RADIUS)
-**;**
+;
-===== Example_2 Using mocap markers to define the corners =====
+</code>
-**Introduced in Visual3D Version 5**
+==== Example 2: Modify force platform corners directly ====
-Consider the following markers to be placed on the corners of a force platform in the standing trial.
-FP1_1, FP1_2, FP1_3, FP1_4
+This example is possible in **Visual3D Version 5 or later**.
-MARKER_RADIUS is a model metric containing the radius of the markers.
-! If the force platform parameters have already been defined, we only need to modify the corners.
-! Note that the markers are in meters, but the following command requires millimeters
-\\
+Consider the following markers to be placed on the corners of a force platform in the standing trial:
+  * FP1_1
+  * FP1_2
+  * FP1_3
+  * FP1_4
-[[Visual3D:Documentation:Pipeline:Force_Commands:Modify_Force_Platform_Parameters|Modify_Force_Platform_Parameters]]
+Given MARKER_RADIUS is a [[visual3d:documentation:modeling:model_metrics|model metric]] containing the radius of the markers, use the following pipeline command:
+<code>
+! If the force platform parameters have already been defined, we only need to modify the corners.
+! Note that the markers are in meters, but the following command requires millimeters
+Modify_Force_Platform_Parameters
 /FP_USED=1
 /FP_CORNER1= 1000*MODEL::TARGET::FP1_1::X
@@ Line 117: / Line 120: @@
 +1000*MODEL::TARGET::FP1_4::Y
 +1000*(MODEL::TARGET::FP1_4::Z-&::MARKER_RADIUS)
-**;**
+;
+</code>