  There are various methods for extracting iso-surfaces from volumetric data.
Marching cubes or tetrahedra or raytracing methods are mostly used. There are
many specific techniques to increase speed of computation and decrease memory
requirements. Although a precision of iso-surface extraction is very important,
too, it is not mentioned usually. A comparison of the selected methods was made
in different aspects: iso-surface extraction process time, number of triangles
generated and estimation of radius, area and volume errors based on
approximation of a sphere. Surprisingly, experiments proved that there is no
direct relation between precision of extracted and human perception of the
extracted iso-surface
