Very good explanation.
Never said anything about being a figment of imagination, but NEMA is ONLY a
communications protocol, the rest, as you stated, is done in the firmware
and software.

"Dennis Pogson" wrote in message
...
MikeT wrote:
Well, I am no expert, BUT,
NEMA is a protocol for outputting differences between course, turning
info, etc, nothing o do with mapping at all. The Maps actually take a
proportionally lat-lon coordinate, and place this in the place where
they belong on a particular mapping system, BBS, and a bunch of new
ones. They are apples and oranges.

So these NMEA sentences that I see being downloaded from my Garmin,
complete
with lat./long. co-ords, are just a figment of my imagination? My mapping
progarm is pulling them out of thin air?

In reality, your mapping program reads the position co-ords from the GPS
and
translates this into a pixel position on the map. The co-relation between
the pixel position and the lat./lon. co-ords is done when you calibrate
the
map in that particular program.

NEMA is just a communication language that identifies certain things
such as errors in course and sends that error out to be plotted in
radar, or autopilot, etc it does not care at all about any maps that
were provided to you for visual ease of use.

Allot of the newer mapping systems are in fact usable among the
different manufacturers, but there are different methods for creating
layers which allow a position to be indicated on a map that translate
to a DMS position.

But, maps ARE not all interchangeable, period, I have had 3 GPS
receivers and have had to have 3 different formats of software in
order to be able to properly correlate a position to a map.

You can get a position off of just about any mapping system on a PC,
but you may have to manually upload that info to a GPS.

Now as far as just the GPS receiver attached to a PC, there is
probably much more flexibility as to software compatibility as the PC
can handle translations, but to say all of them are interchangeable
is probably a incorrect and un-safe statement.

Mike
"Gualtier Malde (Chuck)" wrote in message
...
I came across a Garmin 18 WAAS-enhanced GPS for a laptop. That led
me to search for other types and brands, but I didn't get many
answers.

These units are sold with road use in mind. What if I wanted to use
one with nautical charts? Does anyone know if the BSB and roadmap
formats are the same?

I'd like to hear from anyone who might be using this equipment.

--
Satellite photocharts of the UK & Ireland
available, excellent detail and accurate
calibration using Oziexplorer.
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