| For centuries navigators had to devote most of | | | | are likely to have been designed specifically for |
| their time and effort to working out their position. | | | | use as a chart plotter, and although the choice of |
| Now, to a very large extent, GPS can be relied | | | | cartography is limited - usually to one particular |
| upon to take care of that. The snag is that even | | | | supplier and one particular type of cartridge - the |
| with quick plotting techniques, human navigator | | | | coverage is generally good and cartridges are |
| working on a paper chart can't hope to keep up | | | | readily available. |
| with the flow of information available from GPS | | | | PC plotters consist of specialist plotting software |
| receivers. | | | | that can be loaded into almost any personal |
| One solution is to use chart plotters to display | | | | computer, though laptops are the most popular |
| current position on an electronic chart. Of course, | | | | for the job. |
| chartplotters have their drawbacks, but their | | | | PC plotters are good because the initial outlay is |
| great strengths are that they update the position | | | | relatively low (especially if you already own a |
| continuously, without human intervention, and | | | | suitable computer) and because the computer |
| without introducing such very human errors as | | | | itself is very much more versatile than a |
| plotting 55°45'.6N instead of 55°46'.5N. | | | | dedicated plotter. Some PC software can use |
| The simplest chartplotters do no more than this. | | | | cartography from a variety of different suppliers, |
| Most, however, allow you to mark waypoints, | | | | but additional or updated charts are not always |
| plan routes, and measure directions and distances, | | | | readily available. |
| while some can work out the course to steer to | | | | Raster charts v vector charts |
| allow for tidal streams, or even plan the optimum | | | | Although there are many different suppliers of |
| route to follow to allow for forecast changes in | | | | electronic charts, the charts themselves can be |
| wind strength and direction. They can then show | | | | divided into two main groups: raster and vector. |
| how your actual position compares with your plan, | | | | Raster charts can be regarded as electronic |
| give simple steering instructions to a human | | | | photocopies of paper charts, produced by |
| helmsman, or control an autopilot. | | | | scanning a master copy of a paper chart, in much |
| Chart plotters are a combination of three main | | | | the same way as a fax machine scans a |
| groups of components:o the hardwareo the | | | | document that is about to be sent. The chart is |
| cartographyo the software | | | | broken down into a vast number of tiny dots |
| The hardware is the physical equipment (the | | | | (pixels), and the position and colour of each pixel is |
| casing, display, control panel, and so on) and the | | | | recorded. Instead of sending this information |
| internal electronics, such as the power supply, | | | | down a telephone line, as a fax machine does, the |
| processor and memory. They may be designed | | | | chart scanner stores it on the cartographer's |
| from the outset as chart plotters; they may be | | | | computer, from where it can be copied onto |
| combined with some other equipment such as | | | | floppy discs or CD ROMS, and supplied to |
| marine radar or autopilots; or they can be | | | | customers. |
| desktop or laptop PCs or even PDAs (Personal | | | | Raster charts are relatively cheap and simple to |
| Digital Assistants). | | | | make, but each chart uses up a lot of memory |
| The cartography refers to the electronic charts. | | | | or disc space. Because they are electronically |
| They are available from various sources, in | | | | copied straight from the paper chart, they are |
| different formats and on different media, such as | | | | familiar in appearance, and contain exactly the |
| CD ROMs, floppy discs, PCMCIA cards, flash | | | | same information: nothing is added or taken away. |
| memory cards, or custom-made cartridges of | | | | The drawback of this is that they can only be |
| various shapes and sizes. | | | | used effectively at about the same scale as the |
| The software is the link between the two, | | | | original chart: if you zoom in, then letters and |
| converting the electronic cartography into a form | | | | symbols become huge, but without any extra |
| which can be displayed on the screen, enabling us | | | | detail becoming visible; while if you zoom out, |
| to carry out navigational tasks, and | | | | names and symbols become illegible. |
| communicating with other electronic equipment | | | | Vector charts are produced by electronically |
| such as a GPS receiver and autopilot. | | | | tracing raster charts. The fundamental difference |
| Dedicated hardware v PC | | | | is that lines are not stored as strings of darkened |
| In general terms, most dedicated hardware | | | | pixels, but as lines. Vector charts originally became |
| plotters are produced by specialist marine | | | | popular for small boat hardware plotters because |
| electronics companies, and are supplied with their | | | | although they are more expensive to produce, |
| own software already installed. | | | | they occupy much less memory. The vector |
| Dedicated hardware is good because it is rugged | | | | format also allows more flexibility in the way the |
| and waterproof (at least to some extent) and is | | | | chart is used: a vector chart can be zoomed in or |
| designed to operate from an unreliable 12-volt | | | | out much further than a raster chart, but the |
| supply. Its control panel and operating procedures | | | | letters and symbols always stay the same size. |