Methods for piecewise-linear and piecewise-affine transformations parameter decoupling in High Dimensional Touchpad (HDTP) user touch interfaces including those with multitouch capabilities are described. A calculation chain provides a first-order calculation of a subset of a collection of touch parameters (including for example left-right, front-back, downward pressure, roll angle, pitch angle, yaw angle) responsive in real-time to user touch on a touch-responsive sensor array. A piecewise-affine transformation is applied to these first-order calculations to produce parameter decoupling. The piecewise-affine transformation can be structured to depend only on current numerical values from the first-order calculation. Alternatively, the piecewise-affine transformation can be structured to additionally depend on the positive or negative direction of change over time of at least one numerical value from the first-order calculation, thereby providing a correction for hysteresis effects.