Bookmark and Share Email this page Email Print this page Print Feed Feed

Raster charts go to higher resolution

Oct 29, 2013
An example of a RNC at 400 dpi

An example of a RNC at 400 dpi

NOAA

Recently NOAA has released a flurry of news regarding their chart products. First there was an announcement that the agency will no longer print charts for chart dealers to hold in inventory, then a press release that most nautical charts will be available for free download as PDFs. Now NOAA, via its Coast Survey arm that is rsponsible for nautical charts, has announced that NOAA raster navigational charts (RNC) will go from 254 dots per inch DPI to 400 dpi. This higher resolution will reduce the "jaggies" when the charts are zoomed and will generally make them easier to read. 

From the press release: The NOAA RNC is a geo-referenced digital image of the traditional paper chart. When it comes to digital graphics, higher resolution is generally better than lower resolution. Dots per inch (dpi) measures the image resolution: the higher the dpi, the better the resolution, the clearer the image. Today, cartographers at Coast Survey are busy improving the resolution of NOAA RNCs, increasing the chart images from the current 254 dpi to 400 dpi. This change improves the clarity, readability, and aesthetics of this highly popular digital charting product.

Coast Survey maintains over a thousand RNCs that are available as free downloads. Our Marine Chart Division is transitioning the entire suite, updating and checking quality on all the charts, and we expect all RNCs to be upgraded to the 400 dpi by January 2014. Don’t worry, we aren’t taking anything offline. You won’t even notice that we’re changing the RNCs, except that you’ll see clearer images after your chart has been changed to 400 dpi.

This improvement in RNC clarity will make it easier and faster for mariners to interpret the information on the chart. Less time puzzling through ragged graphics means more time to increase situational awareness.
We’ve included a 400 dpi test dataset on the NOAA RNC webpage, so RNC users can give it a try. The test dataset includes BSBs for Detroit, Long Island Sound, Puget Sound, and Tampa Bay. We hope that users and developers will let us know if you discover any problems with the test dataset. (Submit comments here.) We’ve listed some frequently asked questions below.

FAQs
Does this change the actual format of the RNC? 
No. The only change is the resolution of the chart image.

Will higher resolution files have bigger file sizes? 
The average increase in file size is around 50 percent, but that is easily handled by today’s computers, mobile apps, and display systems.

When will all the high-resolution RNCs be available for public download? 
If the transition goes as planned, NOAA expects to upgrade all RNCs to 400 dpi by the end of 2013.

I currently use the NOAA RNC suite in my chart plotter. Will the high-resolution RNCs work as well?
We expect no compatibility issues in this upgrade. If you do have technical problems with this upgrade, contact your software provider for technical assistance. We encourage software providers to let us know of any difficulties during the testing period. Submit comments and questions to NOAA’s Nautical Inquiry & Comment System.
 

Add your comment: