9 NAVIGATION ELECTRONIC CARTOGRAPHY
It was inevitable that electronic charts would eventually challenge the traditional role of paper ones. When they first appeared they were very expensive but this is another market where street prices have fallen dramatically.
When combined with a GPS you can not only see where you are at any time, but also where you’ve been, since your progress leaves a sort of snail trail behind it. Cartography is the art and science of map-making and in the electronic form there are two distinct types:
Raster These are scanned from paper charts and therefore have much the same look about them. Since scanning is a fast and uncomplicated process, raster charts are relatively cheap to produce but they are heavy users of computer memory – though this has become less important when handled by the larger memories of modern computers.
And there are some limitations. Because the image is a copy of a paper chart, corrections can only be made after an updated chart is issued.
Vector The production of vector charts is a painstaking business. It involves plotting each feature – for instance, the coastline and depth contours – as a series of dots that will later be joined up by a computer to form visible lines. The information originally came from conventional cartography but the plotting process digitises the data directly into a computer file. Because only the dots, rather than the complete lines, are recorded, vector charts need much less memory. An important plus for the vector type is that information can be stored on different layers, which can either be switched on or off at will or will do so automatically as you zoom in and out. This means, for example, that such features as inshore depth soundings or buoys won’t clutter the screen when zoomed out, but will suddenly appear when you zoom in. Also, ‘interrogation’ is possible. This means that when you move the cursor over a feature a window will open to tell you more about it.
Correction of vector charts can be done simply by changing the computer data – a relatively easy task.
Chart plotting hardware
The choice is between running your electronic charts on a laptop computer or on a dedicated chart plotter. Both offer advantages, but most angling boat skippers would choose the latter since marine chart plotters (as opposed to the car type which are very similar) are almost invariably weatherproof.
But there’s little doubt which way the technology is leading us. The expectation is that boats will have a multi-purpose console (or consoles) that will display all important information: charts, radar, speed, depth, fish finding, water temperature, oil pressure and so on. And that’s not a prediction – the equipment is here today and is likely to become more and more affordable as the years roll by.
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It would be difficult to carry as many paper charts as a chart plotter will hold
RYA Seamanship for Sea Anglers
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