Method for filtering a measurement data set usable for specifying and/or verifying an internal feature of a workpiece, the method comprising the following steps: - providing a measurement data set comprising a plurality of measurement points of the internal feature; - providing an auxiliary feature which represents an ideal estimate for the internal feature of the workpiece; - mirroring each measurement point of the measurement data set on a boundary element of the auxiliary feature, thereby generating a first modified data set comprising a plurality of first modified measurement points (P'); - determining a convex hull of the first modified measurement points (P') and projecting the first modified measurement points (P') onto the determined convex hull, thereby generating a second modified data set comprising a plurality of second modified measurement points (P"); and - mirroring each second modified measurement point (P") on the boundary element of the auxiliary feature, thereby generating a filtered measurement data set comprising a plurality of filtered measurement points (P′′′); wherein mirroring each measurement point of the measurement data set on a boundary element of the auxiliary feature comprises: - for each measurement point, defining a corresponding first reflect point on the boundary element of the auxiliary feature; - for each measurement point, determining a corresponding first distance between the measurement point and the corresponding first reflect point; and - generating the first modified data set by determining, for each measurement point, a first modified measurement point (P'), wherein the first modified measurement point (P') corresponds to a mirrored measurement point which is obtained by moving the measurement point across the corresponding first reflect point by two times of the determined corresponding first distance, and wherein mirroring each second modified measurement point (P") of the second modified data set on the boundary element of the auxiliary feature comprises: - for each second modified measurement point (P"), defining a corresponding second reflect point on the boundary element of the auxiliary feature; - for each second modified measurement point (P"), determining a corresponding second distance between the second modified measurement point (P") and the corresponding second reflect point; and - generating the filtered measurement data set by determining, for each second modified measurement point (P"), a filtered measurement point (P′′′), wherein the filtered measurement point (P′′′) corresponds to a back-mirrored point which is obtained by moving the second modified measurement point (P") across the corresponding second reflect point by two times of the determined corresponding second distance. - providing a measurement data set comprising a plurality of measurement points of the internal feature; - providing an auxiliary feature which represents an ideal estimate for the internal feature of the workpiece; - mirroring each measurement point of the measurement data set on a boundary element of the auxiliary feature, thereby generating a first modified data set comprising a plurality of first modified measurement points (P'); - determining a convex hull of the first modified measurement points (P') and projecting the first modified measurement points (P') onto the determined convex hull, thereby generating a second modified data set comprising a plurality of second modified measurement points (P"); and - mirroring each second modified measurement point (P") on the boundary element of the auxiliary feature, thereby generating a filtered measurement data set comprising a plurality of filtered measurement points (P′′′); - for each measurement point, defining a corresponding first reflect point on the boundary element of the auxiliary feature; - for each measurement point, determining a corresponding first distance between the measurement point and the corresponding first reflect point; and - generating the first modified data set by determining, for each measurement point, a first modified measurement point (P'), wherein the first modified measurement point (P') corresponds to a mirrored measurement point which is obtained by moving the measurement point across the corresponding first reflect point by two times of the determined corresponding first distance, and wherein mirroring each second modified measurement point (P") of the second modified data set on the boundary element of the auxiliary feature comprises: - for each second modified measurement point (P"), defining a corresponding second reflect point on the boundary element of the auxiliary feature; - for each second modified measurement point (P"), determining a corresponding second distance between the second modified measurement point (P") and the corresponding second reflect point; and - generating the filtered measurement data set by determining, for each second modified measurement point (P"), a filtered measurement point (P′′′), wherein the filtered measurement point (P′′′) corresponds to a back-mirrored point which is obtained by moving the second modified measurement point (P") across the corresponding second reflect point by two times of the determined corresponding second distance.