DNC® Production

Who is responsible for producing DNC®?
NGA is responsible for the DNC® database and VDU updates.

What are the sources used in compiling DNC®?
Standard U.S., foreign and NGA hardcopy charts, Notice to Mariners, imagery, hydrographic surveys and other miscellaneous sources.

How will DNC® be updated and maintained?
DNC® will be updated with new source material and Notice to Mariners. The DNC® maintenance environment will be able to convert any new source materials such as bathymetry, imagery, Notice to Mariners, new foreign charts, etc. for inclusion in the DNC® database. These changes will come out in new edition DNC® CDs and by VDU.

What is VDU?
VDU or VPF Database Update is NGA's method of updating existing DNC® data. NGA will baseline a DNC® CD, which will have to be stored on your computer's hard drive. VDU patches can then be applied via CD or NGA Gateway, which will automatically update your DNC® data. The VDU update system uses a patch method similar to the method used by many commercial software providers, e.g., virus software providers, wherein only the changes to the database are applied thereby reducing the amount of data to be communicated. DNC® patches are available by individual DNC® libraries which reduces the file update size significantly and allows the user to acquire updates for only the areas needed. VDU patches are cumulative so, once the user applies a patch, all corrections since the base CD was issued will have been applied. On occasion, when a new edition baseline CD is produced, an edition patch will be available with all changes to all libraries since the previous edition CD. The nice feature of this system is that the individual Notices to Mariners are applied centrally within NGA and the user only needs to select the libraries for automatic updating. NGA is also implementing a graphic system to indicate to the user which charts are up-to-date and authorized for paperless navigation and which DNC® are only authorized for situational awareness, i.e., those for which up-to-date paper chart navigation is still required.

When will updates be available?
Currently all 29 DNC® CD-ROMs are updated and maintained by VDU. These VDU Patches are updated and posted on the DNC® website on a monthly cycle, which include all changes that have occurred since the baseline. NGA also provides on the DNC® Website information regarding VDU application as well as the next scheduled VDU posting.

Why can’t I view .rtp files?
.rtp files are the format files for VDU patches which contain the cumulative binary changes for the corresponding DNC® edition or library. These files are not viewable, but are intended to be used with the corresponding DNC® edition or library and the VDU Patch executable supplied by NGA in an effort to update the DNC® data.

How is quality control ensured in producing DNC®?
NGA, as a recognized government hydrographic organization, with representation to both IHO and IMO, has well over 160 years experience in compiling and producing high quality standard nautical charts and publications. Software validation helps ensure the data integrity of the final DNC® product.

How does NGA get the data to build DNC® and is foreign data less accurate than that in the US?
NGA shares maritime safety information with any country desiring to promote navigational safety. In the U.S., NOAA [NOS], the U.S. Army Corps of Engineers and the U.S. Coast Guard are major suppliers of data. Also, the Navy (Naval Oceanographic Office) conducts hydrographic surveys in data deficient areas around the world in cooperation with many foreign countries. Navy provides this data to NGA for new or revised nautical charts. All Navy data is incorporated into the latest editions of DNC®. Foreign data is handled with care, regarding language issues and geodetic accuracy needs and is incorporated into the DNC® libraries. All foreign sources used with DNC® are updated with the corresponding foreign Notice to Mariners which are then included in the VDU patches.

Is it more economical to produce, maintain and distribute digital charts instead of paper charts?
Yes. The development of the DNC® database has been expensive, but improvements throughout our process has resulted in contract costs being reduced significantly Maintenance of the digital database will be considerably more economical than recompiling and distributing paper charts and applying weekly Notices to Mariners. Digital data is much more versatile and provide more valued information. NGA is currently evaluating EPOD (Electronic Print On Demand) technology which will enable users to print charts from DNC®. This capability will provide hardcopy alternatives to customers that want to use DNC®, but do not have Electronic Chart Display capability.