On Thu, Jul 29, 2010 at 6:00 PM, Chris <[email protected]> wrote: > I have done some additional test and believe that what you are > describing (and what I intially suspected) is correct. However, > I think this is a really a software glitch because 0 MPH is a boundary > condition and the software should be smart enough to disregard > normal position variation in sequential GPS fixes at very low speeds.
Okay, so we tell the GPS to ignore any position fixes it sees until it can calculate that it is moving at 5 mph or better... So how do we determine if we are moving at better than the threshold speed if we are ignoring new positions until we are moving? Kind of a catch 22 situation. What if we are moving at a rate below the threshold value? How far do we let the position deviate from what we think is the actual position before we announce that we are at a new location? Obviously the 5 mph rate above is probably a little high. There are GPS units out there that attempt to figure out if the "wandering" is due to calculations, or actual user movement, but those units will by design have to ignore some user induced movements in order to try and cover up the calculated errors. SmartBeaconing and CornerPegging were designed and implemented on resource poor devices many years ago. There wasn't a lot of processor power, nor memory available for sophisticated routines to attempt to eliminate GPS "wandering", nor was there any desire to do so, as SmartBeaconing and CornerPegging were conceived as a way to have vehicular based trackers automatically back off their reporting rates when they slowed down, yet still report the important events as they happened. This was at a time when people set their trackers to beacon every minute or two, and would leave them on 24 hours a day. The airwaves were flooded with vehicles parked in driveways or parking lots screaming out all day long "I'm still here!". You are trying to design a system to drive a finishing nail with a 20 lb sledgehammer... your fingers are going to get sore. What you need to do, is to come up with a routine that not only allows you to continuously vary your beacon rate similar to SmartBeaconing, but also does the fuzzy decision making for when the rate of real position change is less than the variability due to RF vagaries. Get that routine fleshed out, and polished up, and it will be the next best thing since SmartBeaconing... (Uh-oh, I'm going to upset Lynn with his Genius routine!) James VE6SRV
