A curtain coating method including forming a curtain including a coating material. A coated web is formed by coating a moving primary web with the coating material. The curtain and the primary web meet at a contact line. A primary pattern is projected on a material layer. The material layer moves with respect to the contact line. The primary pattern includes a first pointer feature. A first image is captured. The first image includes a first sub-image of the first pointer feature. The position of the first sub-image in the first image is detected. Distance information is provided by comparing the detected position of the first sub-image with a reference position.