1. A method for measuring the height of a three-dimensional surface feature extending from a base in a substrate, comprising the following steps: producing a height map of the feature with respect to the base and a phase map of the feature; producing a fringe-order map of the feature with respect to the base; analyzing the fringe-order map to determine a most prevalent fringe order of the feature; and producing a corrected height map of the feature by assigning said most prevalent fringe order to corresponding pixels in the phase map of the feature.