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.
SENC delivery
The WEND system has established an optional distribution mechanism called SENC delivery. This is in addition to the standard ENC distribution. In this case, the RENC delivers the ENCs to a chart data distributor who then performs the ENC-to-SENC conversion (that otherwise would have to happen inside the ECDIS), and deliver the SENCs to the end user.
However, it is up to the individual Hydrographic Offices to decide whether they allow the ENCs for their waters to be distributed in SENC format.
To the date of this publication SENC delivery has only been accepted by a few nations.
It is possible for the ECDIS to determine if the SENC data being displayed is from either an official ENC or a private source by use of the Agency Code (a two character combination which is unique for any data producer) embedded in the data.
Using this code the ECDIS is able to inform the mariners that they must navigate with an official up to date paper chart if SENC data from a private source is in use.
