Re: Gpsd clear fix and merge fix

[raaj lokanathan]

Does this causes the NaN values?

Are there any ways to not to use the isfinite checking in my application? Because I believe  since gpsd already done the isfinite checking when it store it into the structure why it has to do the checking in the application too?

On Thu, 2 Apr 2020 at 8:37 AM, Gary E. Miller <address@hidden> wrote:

Yo raaj!

On Wed, 1 Apr 2020 14:41:28 +0800
raaj lokanathan <address@hidden> wrote:

> I am a bit confuse why is the gpsd is clearing the fix always?

The GNSS receiver takes a bunch of measurements every cycle.  Then it
takes a bit of time to compute a complete fix solution, and then a bit
more time to send the data to gpsd. gpsd collects this into a "fix".
Each fix, with its unique time, is separate from all other fixes.  So
it makes sense that once gpsd is done with one fix, it clears all the
data, and starts over again.

If gpsd starts mushing data from different fixes together, then that
is bad.  If a car or boat thinks its position now, is actually from
many seconds ago, then it thinks it is in the wrong place and could hit
something and do damage.

So gpsd clears between each fix, and the current fix is just the current
fix, and all other data is cleared.

> And how does the merging fix works?

Every GNSS receiver, NMEA, and/or binary, sends data a dribble at a
time.  In NMEA, some data comes from RMC, then some from GLL, etc. gpsd
has to take those bits, as they come in, and merge them into a single
fix with the available data to that moment.

> I don't really understand it.

Few, do.  And you don't need to understand it.  You just need to know
that gpsd gives you the best idea it can of what is happening at the
moment it gives it to you.

RGDS
GARY
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Thanks and regards,

Raaj Lokanathan