Abstract: A data field assigns data values to positions in a multi-dimensional space. The data values on the iso-surface are equal to a predetermined iso-value. The method of the invention is carried out on a sampled data field. The sampled data field assigns sampled data values to lattice positions on a multidimensional lattice in conformity with a sampling of the data field. A method of deriving an iso-surface in a multi-dimensional data field comprises the following steps. A binary shell is derived from the sampled data field. The binary shell comprises cells in the multi-dimensional lattice. Each cell of the binary shell includes lattice positions having a sampled data value larger than the iso-value as well as lattice positions having a sampled data value smaller than the iso-value. A line of sight is chosen in the multi-dimensional space and cells in the binary shell which are intersected by the line of sight are determined.