Maybe you can figure out for use how long one must average the data to get down to a given position accuracy. The fact that you have a poor location is good. You are generating real-world numbers. If I use my GPS I find the location never moves more then a few inches at most. I have a roof mounted antenna and after averaging for an hour the data never gets better.
On Sat, Nov 26, 2011 at 1:20 AM, Hal Murray <[email protected]> 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 74777 > 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 the > 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 by > more than 20 feet in either lat or lon, it's a random number generator. > > Here is the same data with different vertical scales: > http://www.megapathdsl.net/~hmurray/robot/diff.png > http://www.megapathdsl.net/~hmurray/robot/diff-1000.png > http://www.megapathdsl.net/~hmurray/robot/diff-20.png > > Maybe I'll get a chance to collect some data outside in a reasonable > location... > > > -- > These are my opinions, not necessarily my employer's. I hate spam. > > > > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. > -- Chris Albertson Redondo Beach, California _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
