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Old 12-01-2004
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Advanced Electronic Charting


Split-screen technology allows a chart segment to be shown next to a radar, bottom contour, or photo image.
So much has happened in computerized navigation with electronic charts in the last two years that's it's difficult to decide where to start. In my first article about electronic charts, I explained the difference between raster and vector charts. Just in case you missed it, a raster chart is a computer scan of a paper chart while a vector chart is a digitized chart composed of many layers. At that time I also pointed out that the International Maritime Organization (IMO) had only approved the vector-chart format for use with an Electronic Chart Display and Information System (ECDIS). The little brother to ECDIS is the Electronic Charting System (ECS), which formerly used only the raster-chart formats and was not acceptable to the IMO.


Until recently, an ECIDS to IMO standards was only found on ships and megayachts.

Back then there were very few electronic charting systems that met the IMO standards. They were also very expensive and hence only used by large commercial vessels. In early 1999, the IMO allowed the use of raster charts on ECDIS systems as long as the vessel had an up-to-date portfolio of charts. Today, most ECDIS have the capability to use both the raster and vector formats, and in early 2000, the Transas NaviSailor 2400 became the first IMO-certified system. Today there are about a half dozen more and many more systems are being tested for certification. Also, several ECS programs can now use the new vector Electronic Navigation Charts (ENC).

So, what does this IMO certification mean to the average recreational boater with a laptop running a navigation system with raster charts? Perhaps very little, but to the owners of large yachts it means they can now have an inexpensive, certified ECDIS with an Integrated Bridge. More importantly, for all of us it means that electronic charting has come of age and there are at least a half dozen good ECS programs that come close to meeting the IMO's ECDIS standards. In addition, there are several new electronic charts and maps that can enhance your present electronic navigation system.

Perhaps you saw these new charts and maps at some of the boat shows last year. If not, you will definitely see them this year at all the shows. I'm talking about the new aerial-photo maps, the 3-D bathymetric (bottom topography) charts, the Passport World vector charts from Transas also used by Nobletech, the Electronic Navigation Chart (ENC), which is a new vector chart supplied by NOAA and Maptech through a cooperative research and development agreement, and finally the new line of raster charts supplied by SoftChart to compete head-to-head with the NOAA/Maptech charts.

Electronic photo maps supplied by Maptech offer a bird's-eye view of coastal US waters. The photos are taken by the US Geological survey from airplanes flying at 20,000 feet using either black and white or color film. Since color is more expensive, there are more black and white photos available than color. The photos are then given the geometric properties of a map by a process called orthorectification and are then geo-referenced to their actual latitude and longitude. If your are interested, these charts can be viewed on line in a reduced resolution gray scale at www.terraserver.microsoft.com.

"That's right, they are maps and not charts since there is little navigation detail available."

There are several caveats for these maps. That's right, they are maps and not charts since there is little navigation detail available. For safety reasons, you should also view these maps alongside their electronic chart counterparts and never use them alone for navigation and since these photos are only shot every five to seven years, they can be considerably out of date for man-made structures, not to mention, changes due to dredging, storms, and sifting sandbars. Depending on the season when they were taken, these photo maps can hide reefs and rocks. Since these maps are vertical photos, they give you a bird's-eye view, and like a chart, you must make the mental transition to sea-level view. For example, a group of islands that is easily distinguished from a vertical photo map and the chart can often blend into one another or the coastal background when viewed from your boat. For this reason, the oblique photos supplied by Maptech on their Photo Region CDs often give you a better feel for what the harbor entrance will actually look like.


Navionics vector charts are available in several formats.

The 3-D bathymetric charts supplied by Maptech, MaxSea, and SoftChart are primarily aimed at fishermen, but thus can be of value to every boater when navigating in shallow waters away from home port. These charts show a 3-D view of the ocean floor's topography using a green wire framework to display the undersea canyons and ridges. For maximum effectiveness, they should be displayed side-by-side with a standard electronic chart.

Nobletec recently introduced its new vector electronic charts called Passport World Charts. Originally produced by Transas in the early 1990s for the commercial market, these 5,800 worldwide vector charts can fit on one CD. The vector charts produced by Transas, C-Map, and Navionics are the IMO-preferred format because of the ability to manipulate their various layers of data. For example, a contour line on a raster chart is just part of the image whereas the contour line on a vector chart is digital data that can be used with a preset clearance plane, which in turn can set off an alarm when penetrated by a contour line.

The new Electronic Navigation Chart (ENC) from NOAA and Maptech are also vector-based and formatted in the International Hydrographic Organization (IHO) S-57 vector-chart format. Like the latest vector charts from C-Map and Navionics, the new ENC charts are full color and have a chart symbology that's similar to NOAA paper and raster charts. These ENCs are intended for professional mariners and are more accurate than their raster counterparts since they are digitized from original survey data. They also cost more than the raster charts.

SoftChart has a new line of raster charts that also cover the same US waters as Maptech but are more vivid since they use international colors for chart details. They also have mini region packaging so there is no need to buy more charts on a CD than you need.

"The main problem in the past was keeping these electronic charts updated."

The main problem in the past was keeping these electronic charts updated, and every company had the capability of allowing the used ones to be manually updated them from the Notices to Mariners. These computer corrections took up almost the same amount of time as updating the paper charts manually and hence were not always made. The original digital chart data could not be changed and these corrections were accomplished via an overlay on the chart.

Today, however, the digital charts can be updated automatically from a CD or via your computer and the Internet. The overlay corrections can still be used for personal notes, corrections, and information not included in the electronic updates. So if you want to pay for the subscription service, you can always have updated electronic charts on your computer. At sea, these downloads from the Internet can be time-consuming and expensive. Therefore only commercial entities and the military will be using this method. For those boaters who can afford the service, they will be doing the downloads from home prior to a weekend voyage or perhaps from the marina when on a long cruise.


Updated technology at NOAA has led to faster and easier updates.

Recent changes in the method of producing the paper charts have led to this new ability to electronically update  the digital charts on your computer. Today the digital files in NOAA are used to produce the separate films used to print the charts rather than the old method of using the manually updated films to produce the digital image. When NOAA electronically updates a chart, Maptech will compare, pixel by pixel, the new versus the old chart with a resulting file that is composed of only the changes. A subscriber to the update service can go online and download the correction files needed for a particular region. Then the downloaded file is merged with the existing chart files on your computer and a new updated chart is created on your hard drive. This downloaded file can also be used to update your paper charts. The correction patches can be printed out on a color printer and then cut out and pasted to the paper chart in the appropriate places. This sure beats the old manual method of updating charts.

The only catch to all this is the expense. As you would expect, anytime something new is available that will save you both time and work, it tends to be costly. A one-year subscription is $499 per regional CD. But when you consider the value of your boat and the safety of you and your crew, it's a more than fair price. For example, if a CD has 50 charts on it that computes out to less than a dollar per month per chart to always have updated charts for your cruising area. When you consider the value of your time to update them manually, I think you you'll see it's a fair value. In the future, we may see a smaller, less-expensive version designed for recreational boaters and available for individual charts rather than the entire regional CD. The long range goal of NOAA is to get these electronic chart corrections into the hands of all boaters as quickly as possible. In the meantime, we poorer recreational boaters will continue to update our charts the old fashioned wayóby hand.

The other new development is the ability to superimpose your radar images onto your electronic chart. While not entirely brand new, it is new that you can do it for far less today than several years ago.  In my next article, I will explore this development in detail.


Suggested Reading List

  1. Developments in Electronic Charting by Jim Sexton
  2. Electronic Charts 101 by Jim Sexton
  3. Chartplotter Buying Guide by SailNet


Last edited by administrator; 03-03-2008 at 04:47 PM.
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