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

[Joshua Quesenberry]

Usage would be complex navigation and data logging, essentially trying to fill 
as much of gpsdata struct, as possible.

Can anyone explain why in driver_nmea0183.c that GPVTG is intentionally not 
being processed? At line 1797 in the tarball I just pulled it says: "ignore 
Velocity Track made Good".

Thanks,

Josh Q

-----Original Message-----
From: Gary E. Miller [mailto:address@hidden 
Sent: Wednesday, February 7, 2018 11:52 AM
To: Joshua Quesenberry <address@hidden>
Cc: address@hidden
Subject: Re: [gpsd-users] NMEA Minimum Set to Get Most Data

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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