JASON output from gpsd

[Doug Robinson]

Greetings;
I may be not understanding the output of gpsd, but I am under the
impression that the output of the support socket interface is pretty much
plain NEMA 183. The reason I ask is that the latest version of PolarNavy
is not responding and I am attempting to track down the problem. My
assumptions pretty much work with opencpn as it takes the socket interface
and runs with it, adding in the traffic from my AIS receiver as it goes.

When I queried PolarNavy support I received the following information:
"




*PolarView requires data in NMEA 0183 (or N2K) format. As far as I know,
gpsd provides data in their own (xml based) format, at least by default.
You may want to check with gpsd developers to see if it can be configured
to output NMEA 0183 data as well. -- Polar Navy Support*
"

Well since I have used gpsd for several years to interface to this
application, I was a bit surprised. I also attached a snapshot file which
seemed to indicate that PolarNavy had at least read a header line from the
gpsd interface although I know not what it meant. I would hope that my
problems lay with the group permissions and not with an
underlying requirement for the PolarNavy folks to build a custom interface.
Since I am not a programmer the follow on request from PolarNavy support
has me questioning my assumptions.
"








*I don't have any successful user reports of PolarView working with gpsd.
I am also fairly sure about gpsd data format. See this page for
information: [www.catb.org <http://www.catb.org/gpsd/gpsd_json.html>] In
particular, note: "Clients may communicate with gpsd via textual requests
and responses over a socket. <...> The GPSD protocol is built on top of
JSON, JavaScript Object Notation." If you are certain that gpsd provides
data in NMEA 0183 format - could you please let me know how you would
access NMEA 0183 data stream from gpsd? If you have a way to do so - I may
be able to provide instructions to use that data stream in PolarView. --
Polar Navy Support*
"
My answer is to look at the snapshot which in my book should answer the
question as to how I would interface and I expected it to work.....am I off
base here?

Doug Robinson
Master
s/v Nemesis

[Eric S. Raymond]

Post by Doug Robinson
Greetings;
I may be not understanding the output of gpsd, but I am under the
impression that the output of the support socket interface is pretty much
plain NEMA 183.

No, by default it's a custom protocol built on JSON.

There's a "raw" option to allow sentences to be passed though from the
attached devices; if they emit NMEA, it will be NMEA. There's also an
"nmea" option that synthesizes NMEA from whatever the device ships and
includes that in the socket stream.

Read gpsd_json(5), especially the desription of the WATCH command,
for how to set these options.

Post by Doug Robinson
"*PolarView requires data in NMEA 0183 (or N2K) format. As far as I know,
gpsd provides data in their own (xml based) format, at least by default.
You may want to check with gpsd developers to see if it can be configured
to output NMEA 0183 data as well. -- Polar Navy Support*"

Polar Navy Support is deeply confused. There is no mode in which gpsd
emits XML data. There is one *client* program in the distribution that
emits XML.