1. Method for visualizing surface-like structures in volumetric data sets, wherein the visualization is determined by a set of external parameters comprising at least one of position coordinates and directions defining the visualization, the method comprising the steps of a) defining local coordinate systems at sample points of said volumetric data set, the local coordinate systems being different for each sample point, and the sample points defining a first resolution, b) calculating, by a graphic processing unit, gradient vector components (Gai, Gbi, Gci) within said local coordinate systems of said sample points, the calculation performed at the first resolution, c) transforming, by the graphic processing unit, said external parameters from a global coordinate system into said local coordinate systems at selected sample points or at points of a reference grid, the selected sample points or points of the reference grid defining a second resolution less than the first resolution d) using said gradient vector components in said local coordinate system of said sample points for calculating, by the graphic processing unit, a surface normal at a given position of said volumetric data set which is to be shaded, without transforming said gradient vector components to the global coordinate system, and e) calculating, by the graphic processing unit, external parameters from said global coordinate system at said given position by interpolating between the transformed external parameters of said local coordinate systems at said selected sample points or points of a reference grid.