====== FP Type 3 ======

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

{{:fp_type6.jpg}}

==== Channels ====
A Type 3 force platform records 8 ANALOG channels containing the following information:
<code>
[Original Analog] = [Fx12, Fx34, Fy14, Fy23, Fz1, Fz2, Fz3, Fz4]
</code>

Note that a [[visual3d:documentation:pipeline:force_commands:fp_type_7|Type 7]] force platform has the same analog channels as a Type 3 force platform but also includes a CalMatrix. Alternatively, a Type 3 force platform can be thought of as a Type 7 force platform where the CalMatrix is the identity matrix.

==== 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 Groud 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 3 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 3 force platform is calculated as follows:
<code>
COP[X] = (-M[Y]/Force[Z]) + a
COP[Y] = ( M[X]/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 3 force platform is calculated as follows:
<code>
FreeMoment[X] = 0
FreeMoment[Y] = 0
FreeMoment[Z] = M[Z] + Force[Y]*(M[Y]-az0*Force[X]) + Force[X]*(M[X]+az0*Force[Y])
</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.