--- In [email protected], "Fred Hillhouse" <fmhillho...@...> wrote: > > If you look closely at you GPS position, you will notice that it is almost > always showing movement. Of course, I am assuming you have one with a > display but this can be observed on a mouse type and PC as well. This > movement can be caused by several things, such as the satellites are always > changing position, signal strength changing and multipath to only name a > few. At 4 MPH for a high speed setting, it is quite likely you will trigger > a beacon every 61 seconds. > > The resulting data from the GPS can indicate many angles of change as well. > One second, the data may put you north of the last data point and then the > next seconds provide data south of either previous position. This is a 180 > degree direction change which will certainly trip the angle trip point. > Again, it is likely you will get a beacon very often. > > In a perfect world with a GPS showing exact location all the time this never > would happen. > > For more information: > http://gpsinformation.net/multipath.htm > > If your GPS does WAAS it can be better but it will need to see the geo > stationary satellites. > > This link will describe it a bit: > http://gpsinformation.net/waas/acquire-waas-a.html > > Surveyors have a very accurate system. Maybe it would be worthwhile to > investigate the equipment they use. > > > Best regards, > Fred > > > > _____ > > From: [email protected] [mailto:[email protected]] On Behalf > Of Chris > Sent: Wednesday, July 28, 2010 21:25 > To: [email protected] > Subject: [tracker2] Smart Beaconing anomaly at 0 MPH possibly caused by turn > settings > > > > > I was experimenting with a low speed Smart Beacon Profile on a T2 (with > integrated 5W VHF transceiver) and encountered an unexpectedly high > beaconing rate when parked. My settings were as follows: > > Slow Speed: 0.0 MPH TX rate: 7193 sec > High Speed: 4 MPH TX rate: 61 sec > Turn angle: 15 deg Max TX rate: 3 sec > > The shallow turn angle and fast TX rate was set to see if I could reliably > double beacon on street corners. > > The issue arose when parked: Initially, as anticipated, the T2 did not > beacon, but after 10 minutes sitting, it began beaconing every few seconds > until I shut it off. After thinking about what could cause this it occurred > to me that beaconing may be triggered when the uncertainty in sequential GPS > readings causes the T2 turning algorithm to be satisfied. However, since I > don't know the details of the turning algorithm I can only guess how to > avoid this boundary condition. > > Can anyone shed some light on this? >
My initial feeling is that what you describe might well be responsible for the beaconing I observed. However speed was reported as 0 on the individual GPS points. I would have expected that both the GPS and the T2 would be aware of this issue and apply a threshold filter to eliminate spurious speed reports. Still unless I made a user error that I haven't identified, this does seem like a likely explanation.
