Re: [gpsd-dev] ✘NMEA_MAX

[Gary E. Miller]

Yo Eric!

On Mon, 28 Mar 2016 21:06:38 -0400
"Eric S. Raymond" <address@hidden> wrote:

> > And in another twist.  cm accuracy mean lat/lon use 7 digits after
> > the deciaml point, not 6.  I'll dive in to find where that is
> > getting truncated.  With luck it will not break too many
> > regressions...  
> 
> Uh oh. This'll be interesting.

Actually, not too bad yet.  The JSON has been using 9 digits past the
decimal point and that is more than we need.  Looks like most of the
precision loss was confined to the output formatting.  I think all that
code has been consolidated into deg_to_str();

From this wikepedia article:

https://en.wikipedia.org/wiki/Decimal_degrees

At the equator 0.0000001 is 11.132 mm, 7 digits past the decimal
point is about the needed cm precision.

I infer for cm level precision the output formats should be:

    d = DD.ddddddd
    m = DD MM.mmmmmm'
    s = DD MM' SS.sssss"

I made a bad mistake, and 'scons check' did not catch it.  So the test
converage needs to be expanded a bit...

I think what I just pushed is right, but I would appreciate a few folks
double checking my math, and checking for stray side effects.

And all the Skytraq doc reminds me that gpsd needs its own doc depository.

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

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