A device implements a method for estimating the application force of a touching object onto a touch surface in an FTIR-based projection-type touch-sensing apparatus. The apparatus generates projection signals representing radiation that has propagated on a plurality of propagation paths by total internal reflection (TIR) inside a transmissive panel beneath a touch surface of the transmissive panel such that a touching object on the touch surface causes attenuation (frustration) of at least one of the projection signals. The device generates a time series of force values, which represent the application force, based on a time series of magnitude values, which represent a magnitude of a peak in two-dimensional interaction patterns generated by image reconstruction processing of the projection signals, the peak corresponding to the touching object on the touch surface. The force estimation may involve one or more corrections.