Measuring the gap size in the radial brightness distribution resulting from an ALMA observation and in the surface density distribution. The solid line represents the radial brightness profile and the dotted line the surface density of a disk model hosting a planet with η = 0.001 without turbulence (SP1). The dashed line represents the radial brightness profil and the crosses the surface density of correspoding disk model with magnetohydrodynamical turbulence (SPT6). The central star is a Herbig Ae.