An exemplary method involves, in a system comprising a tool that performs a task on a workpiece, a method for determining displacement of the workpiece relative to the tool. Respective displacements of loci of at least a region of the workpiece are mapped using a Goos-Hänchen-insensitive (GH-insensitive) displacement sensor to produce a first set of physical displacement data for the region. Also mapped are respective displacements, from the tool, of the loci using a GH sensitive sensor to produce a second set of optical displacement data for the region. Goodness of fit (GOF) is determined of the second set of data with the first set. According to the GOF, respective GH-correction (GHC) coefficients are determined for at least one locus of the region. When measuring displacement of the at least one locus in the region relative to the tool, the respective GHC coefficient is applied to the measured displacement to reduce an error that otherwise would be present in the measured displacement due to a GH effect.