EFFICIENT TOMOGRAPHIC PROCESSING FOR TOUCH DETERMINATION

Touch sensitivity is enabled using a touch system that comprises a panel configured to conduct signals, e.g. by TIR, along detection lines across a touch surface. A signal processor operates to generate data samples indicative of transmitted signal energy on parallel detection lines at a number of different angles across the touch surface; process the data samples for generation of interpolated Fourier coefficients at grid points in a regular grid in a Fourier domain; and operate a two-dimensional inverse Fourier transform on the interpolated Fourier coefficients so as to generate an interaction pattern for the touch surface. The interpolated Fourier coefficients are generated sequentially for individual groups of grid points. Each individual group comprises grid points that have equal distance to an origin in the regular grid, e.g. grid points that are mapped onto each other by one or ore lines of symmetry in the regular grid. The group-based processing may improve processing speed and/or reduce the need for data storage.