A method for generally continuously calibrating an interactive input system, the interactive input system comprising at least two imaging devices having fields of view encompassing a region of interest, at least one of the imaging devices calibrated using a projection matrix having an associated quality metric, the method comprises estimating new values for parameters of the projection matrix based on a plurality of computed locations of at least one pointer brought into proximity with the region of interest; calculating a new quality metric using the new parameter values; and if the new quality metric is more accurate than the existing quality metric, updating the projection matrix using the new parameter values.