Making charts interactive
Electronic charts come in two basic types, raster and vector. Both types are drawn or compiled using data from actual surveys and information from authorities concerning aids to navigation, restricted zones, navigational hazards (wrecks or submarine cables for example). A Raster chart is a scan of a paper chart and as such has the same clear and easy to use style mariners have been accustomed to. What makes navigation with raster charts appealing is that the updating is automated and GPS position can be overlaid to give real time situational awareness. A vector chart on the other hand is a database that permits a computer generated representation of the chart making use of detailed data that can be further interrogated. Objects on a vector chart can be selected or ‘clicked on’ to reveal further details and the data that is contained within the chart can be accessed by the ECDIS to activate certain features. For example, the depths and contours on a raster chart are mere inanimate pixels but while the vector chart will show the same figures and lines, if an alarm feature relying on depth is activated, the ECDIS can inform the user of any conflict or danger. Zooming is a highly useful feature of modern computing capability and the ECDIS is no different. However, when zooming a raster chart every detail will grow larger and more pixelated making it difficult to interpret. By contrast, zooming on a vector chart will simply move the display to a different scale without any pixilation occurring. If zooming out on a vector chart to the smallest scale, some objects and features may become over-written and it may be necessary for the operator to turn off some layers of detailing. National hydrographic offices are the only official source for chart data for SOLAS and electronic charts produced by official hydrographic offices for use with ECDIS must be vector charts that conform to standards laid down by the International Hydrographic Organization. The key standard that applies to current ENCs is S-57 which covers the data and S-63 which is an S-57 chart with additional security encryption to deter illegal amendments and pirating of ENCs. ECDIS makers have been obliged to incorporate means of dealing with the encryption in their products. Raster charts are not considered as complying with SOLAS requirement for ECDIS but there use may be permitted for navigation in areas where no official ENC exists. A raster chart may also qualify as a back-up for an ECDIS. Although an S-57 ENC is the requirement for SOLAS, manufacturers of ECDIS have devised their own graphics and hardware configurations and the data that is contained within an ENC will need to be converted into a System Electronic Navigation Chart (SENC). Some major distributors of ENCs have developed their own system standards which a number of ECDIS makers have incorporated into their systems. Some- times ECDIS makers refer to products that can operate with several of these distributors as ‘multi-fuel’ ECDIS. There are a number of ECDIS makers that distribute the official AVCS dataset in their own internal SENC format, ChartWorld, Navtor and Transas. Jeppesen also operate a SENC data service in conjunction with Primar. These services can in some instances reduce the ENC installation time as the dataset has come in a converted state. The number of OEMS offering this service is low because of the need for a large install base to make the service profitable as each SENC is proprietary. Not all Hydrographic Offices allow their data to be converted to SENC on shore. S-57 is the current standard for ENC production but the ECDIS makers and the IHO are already looking to the future and a new standard S-100 is in the process of development. S-100 came into force on 1 January 2010 and is the document that explains how the IHO will use and extend the geospatial standards for hydrographic, maritime and related issues. S-100 extends the scope of the existing S-57 Hydrographic Transfer standard. Unlike S-57, S-100 is inherently more flexible and makes provision for such things as the use of imagery and gridded data types, enhanced metadata and multiple encoding formats. It also provides a more flexible and dynamic maintenance regime via a dedicated on-line registry. S-100 provides the data framework for the development of the next generation of ENC products, as well as other related digital products required by the hydrographic, maritime and GIS communities. Work has just been completed at the IHO on the latest version of the presentation library and it is also working on the new ENC standard S-101, derived using S-100. The International Association of Lighthouse Authorities are using S-100 as the basis for the e-Navigation concepts being developed. A new presentation library will mean that new systems will need to incorporate it and older systems may need upgrading. Buyers of ECDIS systems should satisfy themselves that they are purchasing a system that conforms to the latest requirements.