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SoftCharts
digital charts are raster, whereas C-Map and Navionics charts are vector.
Basically, raster charts are simple pictures of familiar paper charts,
while vectors are tracings turned into databases of chart information,
then displayed as graphics by the plotter.
Raster
charts are created by scanning the official works of hydrographic offices,
and some users favor them because they show every detail and nuance laid
down by the original cartographer. It takes tremendous effort for the
various private vector shops to convert all these details into mathematically
defined lines, symbols, and text, but the results take better advantage
of the processing power of plotters (and onboard computers).
The
pros of vector start with cleanly drawn lines and letters and solid colors.
Data is layered, so elements can be turned on and off for clearer presentation
on smaller screens or when zooming out. Numbers are real, so depths can
be shown in meters or feet, even fathoms. Vectors can be turned course
up, and all the soundings and labels will remain right side up—nice
for comparing to a split-screen radar image. Also, data can be attached
to any object on the chart; you’ll learn to move the NavNet cursor
over a buoy or port information symbol to get a small pop-up data window
and access to a full page of information.
The
cons are that “noncritical” data is left off of vector charts
to make the tracing process less expensive. You won’t see much of
the shoreside information that you get on a paper or raster chart. There
is also the possibility of error in the tracing process. I’ve seen
such errors, though minor and in remote areas. Watch out for those! Lastly,
vector charts are ultimately drawn by a machine and thus lack some of
the little niceties a real cartographer is capable of—like placing
an island name just where it won’t get in the way of other data.
In my opinion, they don’t look as good.
C-Map
has recently introduced a new vector specification called NT+ that includes
numerous valuable improvements, and Navionics is planning to introduce
its own new data format “soon.” It’s also worth noting
that new ways of mixing and blending cartography seen in the latest Nobeltec
and RayTech products suggest that the functional differences between raster
and vector will eventually fade away. —B.E.
Got
a marine electronics question? Write to Electronics Q&A, Power
& Motoryacht, 260 Madison Ave., 8th Fl., New York, NY 10016. Fax:
(917) 256-2282. e-mail: PMYElectronics@primediamags.com.
No phone calls please.
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