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Roles of a hydrographic office and GIS/GPS - an outline survey
Marine Navigation
Electronic Navigational Chart (ENC) – Confluence of GIS, GPS and Object Oriented Databases
- The initial objective of Hydrography was safe navigation of ships at sea and in connected waters. It is still its primary objective though its role has expanded considerably since the 1960s. The primary product under this application is a paper navigation chart depicting the coastline, ports and harbours, anchorages, depth contours, selected representative depths, navigational aids like lighthouses, buoys, wrecks and other underwater hazards, nature of sea bottom at intervals, tidal streams etc.
- Two processes primarily determine safety of navigation with reference to the chart particularly in treacherous waters- one, speed of plotting successive ship’s positions on the chart by the mariner and two, speed of dissemination and incorporation of changes to the chart by the charting agency. Delay in either of the two has often resulted in disastrous consequences. It is difficult to think of many other uses of paper geographic data where these two processes are so critical. A novel application of GIS , GPS and satellite communications now allows both the processes to be executed digitally in real time. The product of this application is called an Electronic Navigational Chart (ENC). This is a GIS produced and GIS enabled version of the paper navigational chart. The Electronic Navigational Chart (ENC) and GPS position of ship, when input to a computer system called an Electronic Chart Display and Information System or ECDIS provides a real time graphic display of ship’s position on a video screen along and with respect to the geographical information contained in the ENC.
- The geographic data is intelligent vector data and permits several other functions such as selective displays, querying of individual objects, navigational safety alarms, route planning. The ENC also carries and displays a digital copy of supplementary navigational publications like Sailing Directions or Pilots, the navigational equivalent of a thorough tourist guide for the coast, ports and harbours.
- An outline of the ENC production process is given at Figure A. A paper navigational chart is scanned, geo-referenced, vectorised, and converted to an object oriented format called S57 to create the ENC. The S57 format has been standardised and promulgated by the International Hydrographic Organisation for exchange of hydrographic data. An ENC is one implementation of the S57 standard. This format can be a common link between all data producing and data using agencies on the seas and coastal areas. But more on that later.
- Encryption1 : There is a major issue of data security facing ENC producing nations today. Need is two fold. One is against piracy and another against deliberate tampering with the data. While the commercial aspect is important enough the fact that HOs are liable for the authenticity of the data any unlawful update of the data will pose serious consequences for navigation. There are several impediments in achieving the goal of a security system. Some of these are :-
- Lack of a standardisd encryption system.
- Encryption is not included in the IMO approved standards for ECDIS, (the platform on which the ENC would be displayed.). This may pose a political problem if some nations so desire.
- Potential weak points along the producer to user chain even with encryption, due to possibilities of human collusion.
- Some of the options of implementing a security system without encryption are:-
- Protect, not through encryption, but through signed licence agreements with the readiness to litigate against pirates.
- Watermark the data to trace pirates.
- Unique Result of International Co-operation: This product is a unique result of international co-operation between GIS specialists, cartographers, IHO, and IMO. Only an Electronic Navigational Chart produced under the authority of a Hydrographic office and in the S57 format can be termed as an ENC. Carriage of ENCs by ships in conjunction with ECDIS which conforms to IMO approved standards, has been declared by IMO to meet the statutory requirement under SOLAS convention, to carry updated paper charts.
- Updates to ENCs: The update for electronic charts is envisaged to be carried out initially through CDROMS and later also through the web using INMARSAT maritime communication network. The latter has been successfully tested in North Europe. The current data encapsulation is currently designed as data descriptive interchange format i.e. it contains a description of the meaning of all data elements along with their content. more suited for land communications for efficient teecommunication interchnage the data could also be encoded using ISO 8824 encoding technique which describes data “in context” requiring additional processing based on previously known information on the data format.2
Paper Charts - GIS Improves Speed of Production
While ENC production is at various stages round the world, it has not yet come under extensive use as they have not yet been produced for all sea routes and ports and users want to wait before investing. Even when ENCs do come into primary use by marine shipping it is expected that demand for paper charts would remain. NHO has set up a digital workflow to publish paper charts using the common GIS enabled database created by vectorising the existing portfolio of paper charts for ENC production. The CARIS GIS in addition to producing the S57 dataset also outputs a design file. This is then taken into an Intergraph system to produce colour separates. These files are input to a Computer to Plate imagesetter system which yields the plate ready to print. This has enabled a dramatic reduction in the cycle time for producing a new edition of a chart and production of an entirely new chart.
Field Surveys and GIS /GPS
- GIS and GPS technologies have been used in the field by the Naval Hydrographic Department (NHD) for more than 7 years. Data streams from several sensors onboard survey ships and boats are digitally logged on a common GPS position and time stamp. As the data is collected it can be compared to an underlay of historical data in real time. The raw field data is then fed to a field database for processing.
- The data is normally collected on the WGS84 datum. This is essential as the ENC requires the use of this datum to enable worldwide navigation using GPS on one seamless charting scheme. This is especially important for digital display systems where switch from one chart to another is automatic.
- A wide range of GPS methodologies are used for surveys. GPS, DGPS and RTK are used for afloat surveys. For geodetic control ashore, point positioning methods and baseline methods are used. For mapping the coastline, Kinematic and RTK is normally used. The latter is used onboard a helicopter increasingly. We today have system which pack sensors like echosounders, sonars and GPS in the same portable box. There is a possibility of using Pseudolites to cover areas of signal loss due to obstructions frequently encountered in ports and harbours.
- The field data is received in the NHO on CDROMs. Here it is inspected, validated and approved for usage. Bathymetry is currently maintained as weeded fairsheets the way it is received from the field.
Emerging Utility – Hydrographic Information System
Contemporary technologies of data collection, GIS, RDBMS and data transmission have created a demand for a Hydrographic Information System, based on a central GIS which would be a single unified system capable of capturing and managing hydrographic data along with its core capabilities of information management, survey and chart planning support, data edit, quality control and production of digital charts and updates, paper charts and Notices to Mariners, Nautical publications and updates. It would need to perform most of the functions of a Hydrographic Office from data collection to data dissemination on a single integrated digital platform, integrated in terms of hardware, software, standards, data exchange, organization and policy. It would have to be linked to the internet and to other national databases to realise its full potential in the service of the nation. Many HO s round the world including ours are in various stages of defining such a system. A concept diagram of such a system is depicted at Figure B. The process of digitization of hardcopy data in NHO archives is underway. Definition of the Hydrographic Information System is also being undertaken. This would involve generation of several databases based on Oracle, like Hydrographic Source database, Hydrographic Production Source Database, Hydrographic Product Database, Field Database, Distribution database.
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