On Fri, 19 Aug 2005 11:51:05 +0200, "Meindert Sprang"
wrote:
Because the wind speed and direction are contained in two different SeaTalk
datagrams, the Raymarine converter just translates each datagram into an
NMEA sentence, where the speed is averaged over a longer period, thus the
lower frequency of the sentence. In my multiplexers (www.shipmodul.com), I
collect both datagrams (speed and direction) and output one NMEA sentence
with both fields filled.
Yeah, I've dealt with this issue on both Seatalk and Nexus hardware.
I didn't realize it was explicitily legal for them to do it that way.
Until now I thought it was just a gray area in the spec. Anyway, it
was an easy fix, as you say. I architected my program from the
beginning with data integrity as a major requirement. It takes each
little atomic chunk of NMEA data it acquires (position, speed,
whatever) and treats it separately. When it gets an update, it flag
that datum as valid and starts a timer. If it hasn't received another
update when the timer expires, it flags that datum as invalid and
issues an alarm by turning the relevant display red. So the code was
already 95% there to handle the partial data.
Unfortunately, that won't help the OP, as I haven't addressed changing
the actual NMEA sentences before forwarding them to other apps. It's
not that hard, but I've had a design philosophy of not screwing around
with the raw data. I just display it and hand it on to the next
application or hardware unchanged.
I just fixed another ST50 issue for a customer (or it might be his
multiplexor- not one of yours by the way - since the customer
indicates Seatalk--NMEA conversion is handled by the mux). When the
ST50 is set to display wind speed in m/s, MWV and VWR sentences
indicate that the windspeed is in m/s, but the value is actually in
knots. I correct the data on the fly for display purposes. It was an
interesting problem.
__________________________________________________ __________
Glen "Wiley" Wilson usenet1 SPAMNIX at world wide wiley dot com
To reply, lose the capitals and do the obvious.
Take a look at cpRepeater, my NMEA data integrator, repeater, and
logger at
http://www.worldwidewiley.com/