[time-nuts] DGPS at home
iteration69 at gmail.com
Sat Nov 26 10:35:48 UTC 2011
Those sure look like GNU plot graphs :)
Sorry, i didn't mean to change subjects but i do like gnu plot.
On Sat, Nov 26, 2011 at 4:20 AM, Hal Murray <hmurray at megapathdsl.net> wrote:
> > If you do a test, let us know your findings.
> I think the answer will depend upon how good the location is. If the
> limitation is ionosphere delays, two units near each other should have
> similar errors. If the limitation is multipath, being near each other
> probably won't help much.
> This was a good excuse to make some graphs.
> I have lots of data. Most of it is from units that are indoors and barely
> work. Not surprisingly, the location data is far from good.
> Conveniently, I had a pair of units next to each other and grabbed all the
> NMEA data for over a month. I took a random day. One of the units had
> valid samples, the other had 32439. There were 28651 seconds that had good
> data from both units. I wrote some hack software to merge the data on the
> seconds that overlapped then plotted the difference in lat/lon.
> I've seen samples off by miles. Yes, not many samples but a few. :) Data
> collection may need another filter: don't treat a sample as "good" unless
> previous few samples were good. Remember, this is a crappy location.
> Quick summary for those who don't like graphs, if you ignore anything off
> more than 20 feet in either lat or lon, it's a random number generator.
> Here is the same data with different vertical scales:
> Maybe I'll get a chance to collect some data outside in a reasonable
> These are my opinions, not necessarily my employer's. I hate spam.
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