A nanotopographic measuring device comprises an input arranged to receive sets of measurement data relating to a semiconductor wafer and memory organized into first and second working tables and a results table. A calculation function is capable of establishing a current surface equation from localized gradient values. The equation is established in such a way as to generally minimize a deviation amount between the gradient values calculated from the current surface equation and the localized gradient values. A reconstruction function calculates localized gradient values from a set of measurement data corresponding to an area of the wafer and completes the working tables with these values. It repeatedly calls the calculation function, each time with a part of the values of the first working table and the second working table corresponding to a portion of the area of the wafer to determine, each time, a current surface equation. It completes the results table with the localized height data corresponding to this area, in relation to the reference plane of the wafer, the localized height data being calculated from at least certain of the current surface equations.