The Linear option in the Construct Filter Feature dialog box (Insert | Feature | Constructed | Filter) enables you to filter the data in a feature that is not a circular scan. The deviations affected in this case are perpendicular to the workplane.
For the linear filters, the number of points in the filter set may be less than the number of input points. PC-DMIS removes points at both ends for which not enough data (to the left or right) is available. To compute a valid output point, see "Filter Width box".