3-dimensional (3d) automatic crystal orientation mapping (ACOM) allows to sample parallel 2d section raster images which represent the orientation of crystal grains. The fabric, i.e. the partition of the specimen into 3d crystal grains, can be approximated given its intersections with parallel planes provided by series of 2-dimensional raster orientation images. A method to model the 3d fabric topology and geometry is suggested. In the first step, the different sections have to be corrected for any possible shift in the measurement position. This is most reliably done using a cross-correlation algorithm. Next, an orientation is assigned to each voxel. This is a critical step because the step size in the third dimension is usually not equal to the step size in the planes. Therefore an interpolation procedure is required to fill the voxels in the space between the planes. In this way a 3d orientation image is accomplished by interpolating all 2d raster images in a regular 3d grid called voxel. In the third step, voxels with a common crystallographic orientation are joined to polyhedra partitioning the 3d specimen, where each polyhedron is given in terms of its surfaces, edges, and vertices. At this stage, the polyhedra representing crystal grains exist independent of each other as geometric or graphic objects with their absolute locations in terms of coordinates. Finally, topology is generated as a so-called Map to provide easily accessible information concerning the relative location, i.e. neighborhood relationships of crystal grains. This allows for the fast determination of properties, like the spatial orientation of a grain boundary surface. The procedure is illustrated by an example measured on primary recrystallised silicon steel sheet. Serial sectioning was performed by etching of thin layers of material. After each etch an EBSD map was measured from the same area. Some data on 3d grain size and size distribution are presented and compared to 2d results.