1. A method of enabling touch determination based on an output signal from a touch-sensitive apparatus, the touch-sensitive apparatus including a panel configured to conduct signals from a plurality of incoupling points to a plurality of outcoupling points, thereby defining detection lines that extend across a surface portion of the panel between pairs of incoupling and outcoupling points, the touch-sensitive apparatus further including at least one signal generator coupled to the plurality of incoupling points to generate the signals, and at least one signal detector coupled to the plurality of outcoupling points to generate the output signal, the output signal indicative of interaction between one or more touching objects and one or more of the detection lines, wherein the method comprises: processing the output signal to obtain observed values for a plurality of the detection lines; for each of the plurality of the detection lines computing a normalization value for the detection line as a function of the observed value for the detection line, generating a projected value for the detection line based on a projection function that defines a functional relation between a fitted interaction pattern and the projected value for the detection line, calculating a difference value between the observed value for the detection line and the projected value for the detection line, computing a normalized difference value for the difference value based on the normalization value for the detection line, updating the fitted interaction pattern based on an optimization function to minimize the normalized difference value; and processing the fitted interaction pattern to determine touch interaction.