A method and a measuring instrument for determining the position of an edge to
be measured on a pattern on a substrate are described. A complete, nonlinear model
intensity profile, which identifies the edge to be measured, of a model edge is
ascertained and stored, and a desired edge position xk is defined therein
with subpixel accuracy. A camera image of the substrate having the edge to be measured
is acquired, and a one-dimensional measured intensity profile of the edge to be
measured is determined therefrom. The model intensity profile is identified in
the measured intensity profile with an indication of its location xm relative
to a reference point. The desired position p of the edge to be measured is determined
with subpixel accuracy as p=xm+xk.
