1. An apparatus for detecting a pointer relative to a touch surface comprising: at least two spaced imaging devices having overlapping fields of view, each of said imaging devices having a field of view that looks back at the touch surface such that said imaging devices see said touch surface in three-dimensions as a perspective view including the boundaries of said touch surface, said imaging devices acquiring overlapping images from different viewpoints, each imaging device comparing acquired images with a model describing the boundaries of said touch surface thereby to determine a subset of pixels in each acquired image and processing each pixel subset to generate image data; and processing structure processing image data generated by at least one of said imaging devices to determine the location of the pointer.