====== FP Type 4 ======

A Type 4 force platform is similar to a [[Visual3D:Documentation:Pipeline:Force_Commands:FP_Type_2|Type 2]] force platform except that a [[Visual3D:Documentation:Pipeline:Force_Commands:FP_CALMATRIX|CalMatrix]] is specified.

==== Channels and CalMatrix ====
A Type 4 force platform records 6 ANALOG channels containing the following information:
<code>
[Original Analog]= [Fx_original, Fy_original, Fz_original, Mx_original, My_original, Mz_original]
</code>

A Type 4 force platform also includes a 6x6 CalMatrix (or Inverse Sensitivity Matrix) for pre-multiplying the recorded analog signals before calculating the Ground Reaction Force such that:
<code>
[Fx, Fy, Fz, Mx, My, Mz] = [CalMatrix][Original Analog]
</code>

==== Calculating the Force Signals ====

Calculating the desired force signals in the force platform's coordinate system consists of the following steps:

  - Compute baselines by averaging the analog signals for the specified [[Visual3D:Documentation:Pipeline:Force_Commands:FP_ZERO|FP_ZERO]] frames
  - Subtract each channel's baseline from its recorded signal
  - Pre-multiply the tared analog signals by the CalMatrix
  - Calculate the Ground Reaction Force
  - Apply a threshold
  - Transform the signals into the [[visual3d:documentation:definitions:laboratory_coordinate_system|Laboratory Coordinate System]]

=== Force Vector ===

The Force vector for a Type 4 force platform is calculated as follows:
<code>
Force[X] = Fx
Force[Y] = Fy
Force[Z] = Fz
</code>

==== Compute Center of Pressure ====

The COFP signal for a Type 4 force platform is calculated as follows:
<code>
COP[X]= (ORIGIN[Z]*Force[X] - My) / Force[Z]
COP[Y]= (Mx + ORIGIN[Z]*Force[Y]) / Force[Z]
COP[Z]= ORIGIN[Z]
</code>

==== Compute Free Moment ====

The FreeMoment signal for a Type 4 force platform is calculated as follows:
<code>
FreeMoment[X] = 0
FreeMoment[Y] = 0
FreeMoment[Z] = Mz - ( COP[X]*Force[Y] - COP[Y]*Force[X] )
</code>

=== Transforming Signals into the Laboratory Coordinate System ===

The transformation is defined by the location of the force platform corners, and is common to all force platforms.