The aim of the invention is to determine the local quality of surface data (O) extracted from a volume data set (V) by means of a surface determination method. An environment in the volume data set (V) is determined for each surface point of the surface data (O). Using the curve of the grayscale values of voxels from said environment, at least one quality characteristic (Q) is derived which characterizes the quality of the respective examined surface point. The quality characteristic (Q) or each quality characteristic is output together with coordinates of the respective examined surface point as the method result (O′).