A method for forming a three-dimensional (3D) map of an object, including illuminating the object from a light source so as to project a pattern onto the object, capturing an image of the pattern using an array of detector elements, and processing the captured image so as to measure respective offsets of elements of the pattern in the captured image relative to a reference pattern, the offsets including at least a first offset of a first element of the pattern and a second offset of a second element of the pattern, measured respectively in first and second, mutually-perpendicular directions in a plane of the array. The method further includes computing a correction factor in response to the first offset, applying the correction factor to the second offset so as to find a corrected offset, and computing depth coordinates of the object in response to the corrected offset.