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Re: GPSD For Real Time Application

From: Greg Troxel
Subject: Re: GPSD For Real Time Application
Date: Tue, 31 Dec 2019 15:32:02 -0500
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (berkeley-unix)

Kashyap Gada <address@hidden> writes:

> Couldn't agree with you more but if you look at my first post I've tried to
> restrict my questions to gpsd (leaving aside point 2). Later I may have
> moved off track responding to replies with more questions. Apologies for
> that. But I too don't have all the answers yet. For example - I asked 'gpsd
> accepts all what gps sends to it and forwards it even at higher frequency'
> - Here Gary  responded that gpsd forwards at lower frequency. It isn't
> clear. Does it mean that if we require to interface a gnss receiver with
> more than 10hz update rate the same wont reflect on the client side? If
> yes, then i dont feel it would serve any purpose to someone who want full
> speed update rate.

Gary replied.  But by all means try it, and write some test code to
evaluate what you got back.  You could even submit the test code for
inclusion in the contrib subdir.

>>Keep in mind that with gpsprof, it will show statistics relative to the
>>average observation, which is different from the correct result.  So you
>>may want to higher a surveyor to establish a control point for your
>>static tests.
> Could you please elaborate the last sentence. Did you mean 'hire' a
> surveryor ? If yes could you please explain what the surveyor do?

Sorry, an error of some kind between brain and outgoing bits.  Yes, hire.

Accuracy means the difference between your measurement and the correct
value.  gpsprof will calcuate the average over the input and compare
each position to that average.  But that does not tell you how far that
average is from the correct value.  A receiver that outputs values that
are consistently 10m more north than it should will still look good on

So I am suggesting that you find or establish a physical monument that
has a known location.  And, you will then have to understand the
relationship of your country's surveying datum and what you are getting
with GPS.  In most of the US, the relevant datum is NAD83(2011) epoch
2010.0, which is not what GPS uses.  I have no idea about your local
datums and whether ignoring this is minor or a big deal.  But if you are
talking 5m at 95/99%, it seems unwise to ignore it.

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