====== FP Type 7 ======

A Type 7 force platform records information according to its four corners, which are named 1, 2, 3, and 4.

{{:fp_type6.jpg}}

==== Channels and CalMatrix ====
A Type 7 force platform records 8 ANALOG channels containing the following information:
<code>
[Original Analog] = [Fx12_original, Fx34_original, Fy14_original, Fy23_original, Fz1_original, Fz2_original, Fz3_original, Fz4_original]
</code>

A [[visual3d:documentation:pipeline:force_commands:fp_type_7|Type 7]] force platform also includes an 8x8 CalMatrix (or an Inverse Sensitivity Matrix) such that:
<code>
[Fx12, Fx34, Fy14, Fy23, Fz1, Fz2, Fz3, Fz4]= [CalMatrix][Tared 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
  - 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 7 force platform is calculated as follows:
<code>
Force[X] = Fx12+Fx34
Force[Y] = Fy14+Fy23
Force[Z] = Fz1+Fz2+Fz3+Fz4
</code>

==== Compute Centre of Pressure ====

The COFP signal for a Type 7 force platform is calculated as follows:
<code>
COP[X] = ((az0*Force[X] - M[Y])/Force[Z]) + a
COP[Y] = ((M[X] + az0*Force[Y])/Force[Z]) + b
COP[Z] = az0
</code>

Where

<code>
a = Origin[X]
b = Origin[Y]
az0 = Origin[Z]

M[X] = b*( Fz1 + Fz2 - Fz3 - Fz4) - az0*(Fy14 + Fy23)
M[Y] = a*(-Fz1 + Fz2 + Fz3 - Fz4) + az0*(Fx12 + Fx34)
M[Z] = b*(-Fx12 + Fx34) + a*(Fy14 + Fy23)
</code>

==== Compute Free Moment ====

The FreeMoment signal for a Type 7 force platform is calculated as follows:
<code>
FreeMoment[X] = 0
FreeMoment[Y] = 0
FreeMoment[Z] = M.Z - (COP[X]-a)*Force[Y] + (COP[Y]-b)*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.