[time-nuts] Survey plot as art.

Gary E. Miller gem at rellim.com
Mon Jan 9 00:28:04 EST 2017

Yo Hal!

On Sun, 08 Jan 2017 20:41:25 -0800
Hal Murray <hmurray at megapathdsl.net> wrote:

> gem at rellim.com said:
> >> The Adafruit receiver outputs NMEA format data.  The lat/lon values
> >> are sent as dddmm.mm format (ddd=degrees, mm.mm=minutes)  This
> >> restricts the resolution of the values.     
> > Yes, easy to see the quantization in the Adafruit plot.  
> Something doesn't look quite right.  If the problem was as simple as
> reduced lat/lon resolution, I'd expect the output to be on a grid.
> Instead, what I see is more like a grid that was also missing 1 out
> of N slots.  Where is that coming from?  How do I predict N?

Yes, the raw data shows that it is not using all the possible
precision.  It does skip lat/lons that are representable.

I'm almost at 45N, so that partlly explains why the lat missing codes
are smaller than the lon missing codes.

> I expect it's something like roundoff after the conversion from mm.mm
> to meters, or something like that.

No rounding happening in gpsd.  That is in the raw NMEA.

> Just to make sure we are on the same wavelength, this is the graph
> I'm looking at.
> https://www.febo.com/pipermail/time-nuts/attachments/20170108/051ba89d/attachm
> ent-0003.png


Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
	gem at rellim.com  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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