estimatedMagnetometerMm

Gets estimated magnetometer soft-iron matrix containing scale factors and cross coupling errors., or null if not available. This is the product of matrix Tm containing cross coupling errors and Km containing scaling factors. So tat:

    Mm = [sx    mxy  mxz] = Tm*Km
         [myx   sy   myz]
         [mzx   mzy  sz ]

Where:

    Km = [sx 0   0 ]
         [0  sy  0 ]
         [0  0   sz]

and

    Tm = [1          -alphaXy    alphaXz ]
         [alphaYx    1           -alphaYz]
         [-alphaZx   alphaZy     1       ]

Hence:

    Mm = [sx    mxy  mxz] = Tm*Km =  [sx             -sy * alphaXy   sz * alphaXz ]
         [myx   sy   myz]            [sx * alphaYx   sy              -sz * alphaYz]
         [mzx   mzy  sz ]            [-sx * alphaZx  sy * alphaZy    sz           ]

This instance allows any 3x3 matrix however, typically alphaYx, alphaZx and alphaZy are considered to be zero if the magnetometer z-axis is assumed to be the same as the body z-axis. When this is assumed, myx = mzx = mzy = 0 and the Mm matrix becomes upper diagonal:

    Mm = [sx    mxy  mxz]
         [0     sy   myz]
         [0     0    sz ]

Values of this matrix are unit-less.