Rip Rap October 15, 2002 Issue

Electronic Charting Evolution

The following report was written by RonDoescher, of Westford, MA. It started as a letter to Mailport, and turned into a very interesting brief history of electronic charting. Mr. Doescher is currently a Senior Principal Engineer with the MITRE Corporation. He's a retired U.S. Air Force officer with 20 years of service, and holds a Master of Science degree in electrical engineering from Northeastern University. He spent 10 years helping the U.S. Defense Department develop aircraft mission planning systems.


Your reviews of various leading navigation software products (February 1 and August 1 '02) were interesting and will be a helpful guide for prospective purchasers. You didn't mention datum conversion, however, and this is an especially important consideration because of our emerging reliance upon electronic navigation aid that are referenced to the World Geodetic System-1984(WGS-84) datum.

The accuracy of navigation displays that superimpose route plans and position plots onto georegistered charts, maps, or images is critically dependent on getting the reference datum correctly matched. Most GPS devices have datum conversion algorithms imbedded within their computers. However, the user must ensure a datum match at both the GPS and the navigation software ends to realize their value. MapTech has an internal datum match feature (a "DATUM: OK" flag can be seen in the lower left corner of your illustration) [August 1, page 6], but it wasn't clear if the others you evaluated did.

There are some other subtleties to consider or understand. The WGS-84 model is referenced to mean sea level (MSL). That said, all rendered coastal boundaries and land altitudes are also relative to MSL. Depth contours and markings, however are generally referenced to mean low water (MLW) or mean lower low water (MLLW). Bridge clearances are generally referenced between the bridge height (MSL-based) and the mean high water level (MHW or MHHW).

A map or paper chart produced today by the government is built up from a set of master vellums, each representing a different set of features. Changes or updates to those charts were basically hand-drawn on these vellums, and vector charts (e.g. VMap) were initially digitized from the same vellums used to publish paper charts/maps. As a result, additional errors of feature vs. geoposition registration were sometimes introduced over and above those legally introduced by the original cartographer. Added to that are any errors introduced by datum conversion to the WGS-84 system. Later editions should be drawn from more accurate overhead imagery. I doubt that commercial vector chart producers have access to better data that the U.S. Government.

We all are reaping the payback from the huge investment of tax dollars starting in the mid-1980s that the Defense Department poured into developing and maturing this type of software and data. Many of today's high-tech military aircraft can't even get off the ground without getting a data load from their mission-planning systems. Military aircraft mission planning systems and their databases have followed what I view as a multi-generation evolution that closely tracks the evolution of computer and telecommunications technologies.

The first generation mission planners (mid-'80s) were basically numeric calculators; some used paper maps/charts on a digitizer board (like the "Yeoman") to enter waypoints into a flight plan formatted spreadsheet. In addition, some had avionics "set-up" screens to help with on-board computer initialization. A simple data memory device was used to store information, carry it to the aircraft, and download it into the avionics flight computer.

The second generation introduced early versions of digitized georegistered maps/charts for graphic waypoint entry and situation display. The original digitized map products were scanned at very high resolution - one map/chart on one CD-ROM disc. It also included georegistered gridded databases (altitude) and imagery, and had algorithms to produce the primitive "draped" imagery-over-gridded altitude perspective views that enabled aircrews to "rehearse" a mission. Much work was also done to establish standards on what was a "waypoint," "route," "mark," etc. That may seem trivial, but it was a very complex cultural issue to resolve among aviators of different stripes.

It was about 1989 that the Defense Mapping Agency (now NIMA) started to develop standards for their Compressed Equal Arc-Second Raster Graphic products (CADRG). Clearly, a practical mission planning system now relied upon having a library of controlled products that fitted multiple maps/charts to a CD-ROM (or to an internal hard drive). The "controlled product" aspect meant that government was attempting to get control over the proprietary commercial products rapidly proliferating.

Key to the CADRG were the pixel compression/reduction algorithms developed that allowed '90s-era state-of-the-art graphic machines to load/store/and manipulate them at reasonable speeds and with minimal loss of detail and color contrast. DMA also worked on evolving the CADRG grid methods that allowed seamless "quilting," and the concept of digital "patches" corresponding to the printed Chart Update Manual (CHUM) was developed.

This digitized raster product work quickly evolved into the vector digital product development that is ongoing today. DMA's goal was to completely change the library of all chart masters into a digital vector database; that is, paper chart masters would be computer-drawn vs. maintained manually on vellums.

Third-generation mission planners (late-'90s) began a revolution in the planning software architectures to more effectively utilize the map/chart/imagery/gridded, and other georegistered data becoming available (e.g., weather forecasts from the Air Force Global Weather Center in Omaha). This revolution coincided with the rapid evolution of computer processing, graphic, memory, and data/network connection power. Most of the marine planning/navigation software you've reported on are somewhere between the second and third generation levels in their features.

Fourth-generation systems in development now are emerging as much more distributed processing-based utilizing Web technologies. My guess is that the fifth generation will be more focused on doing planning-on-the-fly directly in the cockpit using mobile Web and improved computer/software technologies.

There's a rich body of military and commercial standards and specifications available now that get into the nitty-gritty specifics. For instance, see www.nima.mil/GandG/pubs.html.

Sailors should understand something of how these products are developed in order to know how far to trust them. As we have all heard, absolute geographic position and depth soundings that appear on many of today's official charts were relative to a local datum and surveys conducted back in the 1700s and 1800s.

The bottom line: Our government has spent hundreds of millions of dollars over the past 20+ years to mature the software and data technologies to support the most sophisticated military aircraft in the world. As a technology spin-off, we the public can now purchase CD-ROMs that include sophisticated "mission planning" software and all scales of charts, imagery, coastal topographic maps, georegistered databases of tide/current/marine facilities, etc. Further, many new businesses have emerged to develop and utilize these technologies, creating new industries and jobs.

I think it's a heck of a story.

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