[DebianGIS-dev] Bug#456149: gpsdrive: Doesn't display my altitude

[Andrew McMillan]

On Mon, 2007-12-17 at 00:10 +0100, Andreas Putzo wrote:
> On Dec 14  20:19, Andrew McMillan wrote:
> > > > GPSDrive is not displaying any altitude reading from my GPS (a Garmin
> > > > 60CSx).  If I telnet to the gpsd port on my local machine I definitely
> > > > do see my altitude coming through on the various data streams available.
> >
> > The GPS itself is a Garmin GPSMap 60 CSx which has a barometric
> > altimeter, can see 10 satellites at the time and is itself displaying
> > altitude and '3D' in it's own status.
> > 
> > Here is a sample from connecting to gpsd now.
> 
> There are no GSA sentences in your sample log and i think gpsdrive
> heavily relies on them to determine whether it knows the altitude or
> not.
> According to the manual of the 60CSx the device should use GSA. 
> Did you set the Serial Data Format in the Interface Setup menu to NMEA
> and if not, can you please verify if the problem persists with this
> setting?

I can set the serial data format to 'NMEA', but it doesn't make a
difference because I'm using the USB connection.  It looks like the
Garmin will only output in the 'Garmin' format via the USB connection,
so gpsdrive is depending on the 'on the fly' translation done by gpsd
for non-NMEA units.

On the other hand, gpsd is certainly *providing* the altitude within the
NMEA output, viz:

$GPGGA,055148,4106.5421,S,17452.2917,E,1,09,,94.9,M,16.836,M,,*42

It looks like the GSA sentence is not produced by gpsd when it's doing
it's on-the-fly translation. It does provide a 'q' command which returns
essentially the same data, so it could probably be added.

On the other hand, perhaps using the GSA message as the sole source of
altitude data seems short-sighted, especially if there are GPS out there
which can provide greater altitude accuracy by combining the GPS data
with other sensors internally.

I've filed bug #456634 against gpsd asking if it can also provide GSA
sentences when synthesizing NMEA output, but I think it would still be
nice if gpsdrive were capable of using the GGA output as an alternative
as well.

Thanks for your help.

Regards,
					Andrew McMillan.

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