1. A method of data processing in relation to an FTIR-based projection-type touch-sensing apparatus, wherein the touch-sensing apparatus is operable to generate projection signals representing radiation that has propagated on a plurality of propagation paths by total internal reflections inside a transmissive panel beneath a touch surface of the transmissive panel such that a touching object on the touch surface causes attenuation of at least one of the projection signals, said method comprising: obtaining a time series of magnitude values representing a magnitude of a peak in two-dimensional interaction patterns generated by image reconstruction processing of the projection signals, the peak corresponding to a touching object on the touch surface; and generating, as a function of the time series of magnitude values, a time series of force values representing the application force of the touching object onto the touch surface.