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Fig.3.10. The main challenge in this part is sorting all pieces which is being described in more detail. In the very first step, all components are introduced to canvas by <Srf_pieces> and all contour lines are also, by <Crv_contours>. Contour lines are sorted by their <length> and their list reversed to have a list of all contour lines from longest one to the shortest. In order to sort all pieces, first they should sort in rows from bottom to top of the shell. Thatâ&#x20AC;&#x2122;s because assembly of them would be in the same order, row by row, from bottom to top. In this case, the helping geometry to sort these pieces is contour lines. Pieces between any two adjacent contour line should be sorted as one row. The next step would be sorting pieces in each row one by one in a circular fashion. So at the end there would be separated groups of pieces sorted in rows and in each row, sorted pieces by their connectivity.