On Sunday, February 24, 2019, 12:28:28 PM PST, Steve Kinney <ad...@pilobilus.net> wrote:
On 2/24/19 2:01 AM, jim bell wrote: > https://www.gpsworld.com/how-to-achieve-1-meter-accuracy-in-android/ > > [partial quote begins] > >> Recent changes in hardware and standards make one-meter accuracy >> possible, in some cases as soon as this year. The transcript of a talk >> given to Android developers earlier this year, this article gives a >> short overview of location in smartphones, introduces Wi-Fi round-trip >> time technology and standards, and then explains the Wi-Fi application >> programming interfaces. >> >> /By Frank van Diggelen, Roy Want and Wei Wang, Android Location, Google/ >That's very relevant indeed - one-meter accuracy would remove the need >to put any kind of 'flag' on top of a dead drop container. Without >retroreflectors or etc. marking packages, broad searches of likely drop >areas would not produce results worth paying for. Yes, I have been considering the retroreflector idea, and while I still think it would be a good idea for 'early' deaddrops, any technique in common use would eventually be sufficiently well-publicized that opponents (cops; thieves) would gradually catch on. A retroflector that can be seen much more than 5 meters away would be convenient, but also risky. Retroreflectors which simply lay on the ground, retroreflective surface up, maybe 1/2 inch in diameter, would still be a useful idea. I imagine that they wouldn't be easily visible from more than 2-3 meters away. Yet another marker would be a sprinkling of a modern powdered clothes-washing detergent around the area of the dropped idea, perhaps up to 10 centimeters away. Such detergents have long (50+years) had phosphorescent materials in them, designed to make clothes brigher. There are UV and near-UV LEDs, say 405 nanometers and shorter, which would make those phosphors glow brightly, visible at least at night. This would have the advantage that they would not be visible more than a few meters away. Another advantage is that they would gradually be washed away, leaving little permanent record. Yet another idea would be to place a relatively prominent object in an area, and then place the drop a defined distance and direction away from that object. >Also buyers would >have no need for a means of finding inconspicuous retroreflectors - just >a 'really good' mobile phone. I have been trying to get an answer to what should be a simple question: Do modern cell phones receive and use WAAS corrections? https://en.wikipedia.org/wiki/Wide_Area_Augmentation_System × WAAS is a type of differential GPS in which the corrections are pre-computed and broadcast by geosynchronous satellites at the same frequency as L1 GPS. This on-frequency transmission has the advantage that no separate correction-signal path should be necessary: a receiver which receives the L1 GPS would, in principle, be able to receive the WAAS corrections. Whereas GPS alone is supposed to be accurate to 5 meters, WAAS corrections are said to result in 1 meter (or less) accuracy. What I haven't heard whether cell phones use this? You'd think you'd get the answer with a google search of 'android waas', but I simply haven't found it. I find discussions of this as early as 2010, but very little is discussed over the years. My next step is to find a 'tracker' program for my phone, and then set the phone down and put it in 'track' mode for a few hours. The size of the scatter-plot should show, not the accuracy, but at least the stability of the signal. This might correlate with the accuracy, At least, if I see a 2-meter diameter scatter, I will be able to expect 1 meter stability. The next step is the phones' addition of the Broadcom BCM47755 GPS chip, https://www.broadcom.com/products/wireless/gnss-gps-socs/bcm47755 that chip which uses both L1 and L5 frequencies. It is already working in a Chinese cell phone, the https://www.gsa.europa.eu/newsroom/news/world-s-first-dual-frequency-gnss-smartphone-hits-market Xiaomi Mi 8, although reading of the first reviews over a half-year ago revealed some early bugs. Accuracies of 30 centimeters are espected. I'm come to the conclusion that anyone _placing_ these dead-drops should do so solely with a stand-alone dedicated GPS+WAAS (or GPS-L1+L5) receiver. It looks too mysterious what a typical Google phone can do to track itself, even turning on 'airplane mode' and taking other precautions. A person hunting these dead-drops could still use a smartphone to find the material. Jim Bell ×
