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Re: [gpsd-users] HDOP and fix mode in the python library

From: Gary E. Miller
Subject: Re: [gpsd-users] HDOP and fix mode in the python library
Date: Wed, 2 Aug 2017 11:18:19 -0700

Yo Fabián!

On Wed, 2 Aug 2017 03:16:20 -0400
Fabián Inostroza <address@hidden> wrote:

> I'm using a SIM5320A 3G+GPS module.

I  see nothing in the SIM5320A datasheet about GPS:

Can you be more specific?

>    1. When the fix is lost, the mode given by the python library
> doesn't get updated, so it is useless.

gpsd only passes on data when it gets data.  Are you saying that
gpsd is getting a 'fix lost' message from your GPS, bit not passing it
on?  Or does the GPS not report NO FIX status?

>    2. Because of (1) I have to use hdop and satellites used to
> determine if the fix is acceptable but when the fix is lost the GPS
> outputs empty hdop, vdop and pdop and keeps outputting satellite
> data. In this situation gpsd uses that information to calculate the
> dilituion values, this sometimes gives very good hdop values but the
> position is completely wrong.

gpsd calculates xDOP internally since so few GPS do it, and do it

Are you saying your GPS does not send gpsd a flag on whether it has
NO FIX. 2D FIX, or 3D FIX?

> 3. When the GPS is stationary it gives
> an empty heading value but gpsd interprets it as 0

Meaningless either way, since the GPS is stationary.

> Note that cgps produces the same results.

As expected.

> Is there a way to disable the hdop calculation done by gpsd without
> recompiling?,

No, but we could explore it as a new feature.  But since the GPS is
outputting emtpy xDOPs that does not seem useful.
> I'm using gpsd 3.16 in an embedded ARM linux board and it is more or
> less difficult to recompile the package

Really?  I recompile gpsd on ARM Linux  sometimes dozens of times a day.

> I have attached a log of the nmea output without fix.

Can you provide a log both with and without fix as one continous

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

            Veritas liberabit vos. -- Quid est veritas?
    "If you can’t measure it, you can’t improve it." - Lord Kelvin

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