1. A method, comprising: forming a curtain comprising a coating material; forming a coated web by coating a moving primary web with the coating material, wherein the curtain and the primary web meet at a contact line; projecting a primary pattern on a material layer, wherein the material layer moves with respect to the contact line, wherein the primary pattern comprises a first pointer feature; capturing a first image comprising a first sub-image of the first pointer feature; detecting the position of the first sub-image in the first image; and providing distance information by comparing the detected position of the first sub-image with a reference position.