Re: [gpsd-users] NMEA Minimum Set to Get Most Data

[Gary E. Miller]

Yo Joshua!

On Wed, 7 Feb 2018 10:11:58 -0500
"Joshua Quesenberry" <address@hidden> wrote:

> I'm playing around with different NMEA messages to see what a good
> minimum set is.

It really depends on what you are trying to do: time keeping, 
antenna testing, simple navigation, complex navigation, etc.

> 1)      Is there a recommended set already?

Many of the different gpsd drivers implement what the code writer
thought was the optimal set for that GPS lingo.

> It looks to me like GPGGA, GPVTG, GPGSA, and GPGSV would be fairly
> encompassing of all of the data shown in cgps.

Yeah, but then gpsmon shows a different set, depending on the GPS lingo.

> One issue I'm running into is that GPSD does not appear to be using
> speed/track information provided by the GPVTG message, rather it only
> appears to be using the information in GPRMC message. I do not want
> to use GPRMC because it lacks information I need that's in GPGGA.

At each new fix time, gpsd clears its data set, then adds new bits of
data as they come in.  Sometimes a later sentence will over write the
data from an early sentence that is more accurate.

You really have to trace out each case, there are way too many to
generalize.

> Also, when I send only GPGGA if I look at the GPSD Client node in ROS
> I see speed populated.

That would be a bug.

> 3)      I assume speed is being interpolated somehow when it's GPGGA
> only?

Nope, not that I have ever seen.  YMMV.

RGDS
GARY
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Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
        address@hidden  Tel:+1 541 382 8588

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