[Flightgear-devel] GPS NMEA ASCII data stream

[marthter <mar...@ya...>]

On 11-07-14 04:16 AM, Stuart Buchanan wrote:
> Martin Muc wrote:
>> Just trying Flight Gear for the first time today.  What a  ridiculously
>> top-notch open source project.  Just awesome.  Congrats and thank  you to
>> everyone who's made it so.
> Glad you like it. It's only as good as the people who contribute.
>
> Sorry I don't have many useful answers for you:
>> Now, first question, on the  downloads page it says:
>>
>>          "64-bit overlay: If you run 64-bit  windows, you can download the self
>> extracting 64-bit version of  FlightGear.  This installs over the top of the
>> standard 32 bit version so  you will need to install that first."
>>
>> What are the benefits of this?   Does it result in faster performance?  reduce
>> memory usage?  what?  Clearly it  is optional since the main fgsetup-2.0.0.exe
>> has installed an run  fine.
> Sorry, I don't know the answer to this. FG (used) to have some memory occupancy
> issues when flying long distances, so there might be a benefit from being able
> to access more memory, but that's a guess.
>> And my main question, has anyone built a mock GPS  display in any of the
>> cockpits? and if so has anyone thought of simulating,  outputting, or logging
>> the NMEA GPS ASCII data stream for time, position,  heading, speed, waypoints,
>> etc?
> Have a look at the Docs/ directory of your FG install point. From memory (I'm
> not at my FG computer right now), there's a README.IO and a README.Protocol file
> which may help.
>> I would be interested in adding this  feature, so I will mention it on -devel,
>> but I thought I'd ask on -users first  and see if it is already implemented,
>> known, used by users who can help/answer  before asking developers.
>>
>> I have checked the FAQ and there's nothing  there mentioning GPS, but I just
>> did a google search with "site:flightgear.org  gps" and these two wiki pages
>> http://wiki.flightgear.org/index.php/GPS   and
>> http://wiki.flightgear.org/GPS_internals  mostly answer my question that  the
>> GPS modelling has been, apparently, thoroughly done.  Great.  So the only
>> question then is has the NMEA ASCII output been considered?
>>
>> ...answering  my own question again, I see NMEA is mentioned as a command line
>> option here http://wiki.flightgear.org/Command_line_options and I've now found
>> it in  the FlightGear launch Wizard too.  Great.
>>
>> Okay, last question, I  just tried sending that NMEA output to a file and it
>> has NMEA sentences for  GPGSA, GPRMC, and GPGGA.  Can it also send GPGLL, GPGSV,
>> and GPVTG, and if so,  how can I enable this?  Or is this a -devel question and
>> I should ask  there?
> I think this is a -devel question.
>
> -Stuart
Okay I've looked at the code in this section and there are three similar 
C++ files for nmea, garmin, and A400 (not sure if I'm remembering that 
last one correctly, I'm at a different machine at the moment).

There is some minor opportunity for code re-use as all three existing 
source files have NMEA checksum calculators, although this is only 20 or 
30 lines of code.

For my own purposes (testing other devices that operate in an aircraft), 
I'll either be modifying the existing nmea source file, or doing a 
copied-and-modified "nmeagll", say, to include GPGLL, GPGSV, and GPVTG.

Is there interest in my contributing this change back?  If I just 
changed how the existing nmea output worked, to add additional lines to 
the output, would a Release Notes note about the change be sufficient? 
or it should be added as a new output protocol (e.g. "nmeagll") to have 
as little effect as possible on anyone currently using nmea?

Thanks.

Martin