Input data requirements In order to process a given trace, the SFM has to read several traces and several gathers depending on the primary and secondary filter widths. Therefore, the SFM requires that the input data be ordered appropriately. The input data must be ordered by GOUPING_TRACE_LITERAL (if used), then by PRIMARY_TRACE_LITERAL and then by SECONDARY_TRACE_LITERAL (if used). The SFM will exit with an exception if it encounters out-of-order traces or gathers.