An ECDIS does not process the ENC content directly for the matter of display. ENCs in S-57 format are optimised to absorb the Hydrographic object information but this structure is not adequate for the fast generation of the resulting computer image on the screen.
In order to get efficient data structures that facilitate the rapid display of ENC data, ECDIS firstly converts each ENC from S-57 ENC format into an internal format called SENC – System ENC – which is optimised for chart image creating routines.
Such routines are not standardised; they are part of the individual software know-how of the ECDIS manufacturers. Consequently the SENC format differs between the ECDIS of different manufacturers. In contrast to the common uniform ENC format the SENC format is proprietary for each ECDIS manufacturer.