Getting Started With Electronic Charting
We receive a lot of inquiries from boaters wanting to get started in PC-based digital navigation, but don't know what's required or how to get started. If you're one of these people, you're in good company.
Electronic navigation programs from companies like Nautical Technologies, Nobeltec and Raymarine and others make real-time navigation available at the flick of a switch and the click of a mouse. Computer-assisted navigation is now commonplace on vessels ranging from weekend cruisers to dedicated offshore passagemakers. The technology has been perfected to the point that it's hard not to marvel at what can be done with a GPS, a laptop computer and some software.
For the purpose of this discussion, we'll focus on PC-based electronic charting, although much of what follows transfers quite accurately to the world of plotters and similar dedicated charting devices. In many ways the personal computer offers a more versatile platform over a dedicated system, starting first with the size and clarity of the available display. Compared to a dedicated plotting system, a PC has more memory, greater disk storage, a more powerful processor, a familiar keyboard and mouse for user input, and it can run sophisticated software to automate navigation chores. Since a computer is also a communications device, PC-based systems can import supplementary external data, like the latest weather information. Finally, it's much easier to design software to support charts in different formats for a computer than it is for a dedicated plotting device. Most plotters rely on chip-based cartography from one or two sources at best (often, a decision which must be made at the time the plotter is purchased). But if a chart can be stored on CD-ROM or DVD-ROM, no doubt a computer program can be written to display and interpret it.
Basically, there are four components of PC-based digital navigation system.
- Laptop Or Desktop Personal Computer
- Electronic Charting System (ECS) Software
- Digital Charts Compatible With The ECS
- GPS (Global Positioning System) Receiver
NOTE: A GPS receiver is not required for viewing charts, but it's use allows real-time navigation, whereby an icon representing your boat moves across the chart to indicate your true position, direction, speed made good, etc. (Or alternately, the boat stays in the center of the screen and the chart moves.) Typically, as you "sail off the current chart", the next chart is retrieved automatically from the library, replacing the current chart on the screen. These, and many other features are dictated by the ECS software, rather than by the charts.
Which computer should you buy? Can I use the one I alreay have? Virtually any of today's new notebook or desktop computers is capable of running charting or communications software as well as most household or office applications. We don't want to give out brand names, but we do suggest that you contact a marine electronics store that specializes in marine navigation and can help you choose a computer that's right for you. If you are just starting out, we would recommend you try to use your current equipment. If you feel the need to upgrade later, you'll have a better idea of what best fits your needs -- both for charting purposes and other onboard needs.
We suggest that the following features be considered in your buying decision to make your computer easier to use and give you more versatility and performance:
- Use your existing laptop or desktop computer. If you're starting from scratch, purchase the best screen you can afford. Active matrix screens are brighter and crisper than dual scan, especially in sunlight. The newer daylight viewable screens are starting to come down in price as demand and competition increase.
- Purchase more RAM versus a faster processor. Most laptops today come with 256 MB RAM as standard, but more and more offer larger standards and upgrades. Increasing RAM will significantly improve system performance for less cost than the next faster processor. Most software packages use disk space as virtual RAM if they need more than you have available as dynamic RAM. But this will slow down your applications considerably.
- If you choose a notebook computer (my recommendation), get one with an internal DVD-ROM player... preferably a player that is also a DVD burner, allowing an easy way to make backups. Electronic charts are less expensive on CD/DVDs and both are more a more robust storage medium. With the use of some good external speakers, you can even play your music CDs through the computer and turn your laptop into a small movie theater.
- Buy a bigger hard drive. Remember: Hardware giveth, software taketh away. If you're purchasing a new system, buy the biggest hard drive you can get. It's usually cheaper to buy it now than upgrade it later, when you run out of space. If you're using an existing system, check the cost to upgrade to a larger capacity.
The actual software that displays and manipulates your electronic charts on screen are called Electronic Charting Systems (ECS, from here on), and are available from companies like Nautical Technologies (CAP'N), Nobeltec (Visual Navigation Suite/Admiral), Raymarine (Raytech Navigator) and many others (see comparison chart).
ECS is available from a wide variety of companies and often a given company will have several offerings.
Nautical Technologies Computerized American Practical Navigator (CAP'N) carries the distinction of being the software of choice for the US Coast Guard and other government agencies. Nobeltec produces their own line of both vector and raster charts, and extend support to many external formats as well. Visual Navigation Suite has many well thought-out features and their Passport vector charts are certainly adequate in most areas (but quality varies by area, check carefully). But Nobeltec's Raster Plus charts are generally less impressive when compared to raster charts available from sources like Softcharts, etc. The strength of Raymarine's Raytech Navigator lies in it's tight integration with other Raymarine instruments. However the software is limited in the types of computer video hardware it supports, especially for the optional radar overlay feature, so careful attention must be paid to the computer system chosen to work with this product.
With the new detailed, full-color electronic charts and computer software to display and manage them, sailors can now bring the highest quality navigation information on board. And with more powerful, less expensive computers, they can own a navigation system that costs less than a single-function chart plotter. Once set up for your needs, the system can also handle an array of functions, from weather fax to communications, not to mention business and recreational uses while on board.
All computer charting and navigation programs work somewhat similarly. The key differences are on how the intricacies of the various navigation techniques, chart updates, nav logs, route planning and different types of electronic charts are handled, as well as the use and display of tide data and current vectors.
First, the software is transferred onto the hard disk of your desktop or notebook computer. The computers serial (Com) port is then connected to a GPS receiver via a supplied cable.
Electronic charts available on both CDs and DVDs can also be loaded onto the computer's hard drive, or the CD-ROM can be accessed directly. When you start the navigation program, it receives the current position from the GPS, displays the appropriate chart for that position and marks your position on the chart with a ship's icon. As the sailboat moves, position changes from the GPS are updated on the chart and you see your vessel's location in real time.
Typically, information such as the vessels heading and speed are also displayed and range and bearings can easily be made using the "rubber band" attached to the vessel's icon. Courses and routes can be entered by pointing and clicking on the chart, or entered manually by typing in coordinates, and then stored for future use.
Several companies offer preplanned coastal routes that can be modified for your departure date and time, boat speed and stops along the way. These routes are displayed on the chart, and the coordinates can be uploaded into the GPS and used via the autopilot for automatic steering.
The great thing about route planning on a computer is the ease and speed of the initial planning and any subsequent changes. For example, if you are heading down the Intracoastal Waterway on a preplanned route, you can enter the time you need to be at a waypoint to make a bridge opening or marina dock time. With a click of the mouse, you can calculate the required departure time.
Routes can be planned on the computer's NOAA raster charts and uploaded to your GPS to be used with its vector charts. This allows the computer to remain safely below at the nav station and the waterproof GPS plotter is used in the cockpit for steering. Granted this is a redundant and expensive navigational system, but using redundant navigation aids is the safest way to go to sea. Besides, if you already own a notebook computer and GPS plotter, the only additional expense is the second set of electronic charts and the navigation software.
The other great benefit of using electronic charts and a computerized navigation program is the wealth of information and data that is immediately available to you. All the information from the coastal pilots, light lists and cruising guides is now available on either the chart CDs or on separate floppies. Some companies include this information on their navigation software CD. With a single click of the mouse you can see this information displayed on the screen.
Electronic charting software is a wonderful navigational aid, but remember it is designed to supplement navigation information from other sources and should not be used as a sole source for navigation. As errors and malfunctions are possible with any electronic system or computer, you must continue to use traditional navigational methods on your paper charts.
Which program would best suit your needs? See the section titled ECS Software for a table of packages from various vendors, for both PC and Mac platforms.
There are primariliy two formats of charts most comonly is use for recreational electronic charting -- Raster Charts and Vector Charts.
Raster Charts are scanned-in digital reproductions of a paper charts... images produced by raster scans of the Mylar master films used to produce the official government paper charts. The Mylar masters are scanned at high resolution, producing a digital video picture that is identical to the paper chart. Geographic information is encoded along with the image to enable positioning of things like a vessel or waypoints on the chart. Using special software, the digital format allows the chart to be displayed on the computer screen and enables the viewer to zoom in or out, easily move around the chart, and incorporate many other functions that cannot be performed with the paper original. Raster images displayed on a screen appear essentially the same as a paper chart, and contain all the same features and information of the original product.
Vector Charts are also digital files, but produced in a very different way. The vector information is a essentially a database of the items that make up the chart -- such as shorelines, buoys, or depth soundings -- along with the location of each feature and details on how it should be displayed. Compared to raster images, vector charts offer some additional flexibility and control because the feature data can be manipulated for display purposes (for example, show any depths less than 10 feet in red, or turn off the display of aids to navigation).
Which is better? Like most things in life, there are advantages and disadvantages to both. It is fair to say that, from a computer's point of view vector charts hold some advantages. Vector charts occupy less disk space, load and display more quickly than raster charts, and can be configured to present information in ways that let one quickly gather information. Raster charts, on the other hand, have the same look and feel of the familiar paper chart and most mariners are more comfortable with this format for general navigation.
But it's more prudent to navigate safely than appease the computer, and in the final analysis raster or vector is not the issue here. The real issue is "what are the best possible electronic charts which can be obtained for the area I plan to cruise, and are they available in a format I can work with?"
Raster or vector, the digital file format used to store and distribute electronic charts is often proprietary, and varies depending on who performed the conversion. This is because in addition to containing the chart itself, the file must take into account other data such as "what chart is this", "what is the chart scale", "what is the reference datum", and so on. Some packagers also include additional features, such as aerial photos or tide and current information, to add value to their brand of cartography. The upshot of it is, different vendors each arrived at their own "best" way of incorporating extra information, or "metadata" into their chart files. The result is a handful of different, usually incompatible formats. But another reason for proprietary formats goes back to the copyright and licensing discussion above.
The GPS receiver could be considered an optional requirement for electronic charting, since you can still display charts without GPS. You can still zoom in and out, scroll, create and save digital waypoints and do many other functions that are not as possible with a paper chart. But a GPS receiver is the component that brings the charting package to life and makes it real-time or dynamic.
Navigating with GPS means having accurate, all-weather, real-time position fixes that are continuously updated. Now introduce GPS with electronic charts and you have a very powerful navigational tool.
With electronic charting, you can view the constantly updated GPS position superimposed on the nautical chart. This spares you the work of plotting latitude and longitude coordinates and laying out your projected courses on a paper chart. At a glance, you can see where you are, where you've been and where you're going.
The Global Positioning System (which does indeed have global coverage) is operated by the Air Force. With 21 satellites now orbiting Earth, GPS is the military's primary radio-navigation system. At any given time, at least four satellites are available to the GPS navigator.
Each satellite transmits a UHF signal. In a manner similar to loran, a GPS receiver calculates position based on the differences in the time that the signals are received. The information from three satellites is as accurate as a calculated, two-dimensional fix. As more satellites are in view, accuracy increases, and even altitude can be established.
The Global Positioning System provides two levels of positioning service: Precise Positioning Service (PPS) and Standard Positioning Service (SPS). The military has access to the encrypted Precise Positioning Service, which provides accuracies of better than 20 meters (66 feet). But for use outside the military, the government applies Selective Availability to the PPS signal. This essentially degrades it to the Standard Positioning Service signal.
The Standard Positioning Service signal provides accuracy of 100 meters (about 330 feet) with 95-percent certainty. This means that if you draw a circle with a 100-meter radius around your actual geographic location, 95 percent of the GPS position measurements for your location would fall within that circle. What this means to you is that your boat's position, as shown on the electronic chart, should be viewed as an approximate location, not an exact one. To be safe draw an imaginary circle of ambiguity with a radius of 100 meters around your on-screen position. It's important to recognize that you could actually be anywhere within that circle. Most ship icons on the electronic chart can be increased in size to represent this circle of ambiguity.
The accuracy of GPS can also be affected by factors such as the tendency of radio signals to bounce from trees, buildings, terrain features and other obstructions (also called multipath propagation); and atmospheric distortion. Through advanced filtering and processing techniques, these effects can be minimized to some extent by GPS receivers.
One of the most vexing problems for new users of charting software is connecting the GPS to the computer so they can communicate. Wouldn't it be great if all you needed to do was connect the blue and the green wire from your GPS to the blue and the green wire from the serial interface cable. Then turn on the computer and see your boat being plotted on the correct computer chart?
But problems occur because of the many GPS manufacturers who interpret the voluntary NMEA 0183 standards in different ways, or because of the myriad types of computers and the way their serial (Com) ports are configured.
In most cases, getting the GPS to "talk" to the computer is fairly simple. But when the two don't, here are some pointers. You'll probably need to first set up the GPS correctly and then find out which wires are used to transmit data. Next, determine which wires on the serial interface cable are used to receive data. This may sound a lot more complicated than it really is. Use the GPS manual and the instructions for the navigation software cable interfacing to guide you. And if you need more help, a quick phone call or visit to their web site can usually clear things up.
Most GPS units have I/O terminals and a cable for connecting to other devices. To transmit information from the GPS to the computer, connect the GPS-signal-ground wire (SG) to the serial-port-ground wire (NMEA B line). Then connect the GPS-transmit-data (TXD) to the serial-port-receive wire (NMEA A line). If you will be uploading data, such as waypoints, from the navigation program into the GPS, you will need to connect the GPS-receive-data (RXD) wire to the serial-transmit wire. Not all navigation programs or GPS units allow you to upload data. These wires are identified by color code in the user's guide.
The navigation and electronic charting programs have a serial interface cable. Most include the cable with the software, though some charge a little extra for it. Software companies also offer (for an additional charge) an optional opto-isolated cable, which we recommend. It isolates your computer from a direct electrical connection and provides a layer of protection.
Next make sure that your GPS unit is set up to transmit the NMEA 0183 standard sentence of RMC or GLL, VTG and DTG. Check your GPS operating manual for instructions on how to do this. If the "talker" (the GPS) isn't speaking the same language as the "listener" (the computer), they will not be able to communicate. The navigation software program will be looking for the correct NMEA sentences on a Com port.
If you are using one of the serial ports for a mouse and the other for a modem, or if your notebook has only one serial port and it's already being used, then you have a problem. But it's easily solved. A serial port PC card will add an extra port and an A/B switch will allow you to use a serial port for the GPS or modem. You may also want to consider using an internal modem.