– The paper deals with fitting of planar patches to 3D laser range data obtained by a mobile robot. The number and the initial position of the patches are unknown, hence their estimation is a challenging problem. It is solved by adding iterated steps of split and merge to a modified Expectation Maximization (EM) algorithm. This allows for precise adjustment of the number of patches, independent from the initial model. The proposed approach overcomes the problem of classical EM, which produces an optimal solution only if the number and position of model components is well estimated.