The places where accuracy matters the most will be impossible to get GPS signals into If there is a so called leaky coax system (used for cell phone operation) they tend to create strange anomalies on GPS tracks. (I know because I often carry a GPS logger when I am in the city just so I can see visually later where Ive been.)
Sometimes when I go into a tunnel it does pick up signal for quite a ways. But the location during that section of trace is never right, its bizarrely wrong.
I have never been on the London Tube but it appears to be exactly like NYC subways in terms of people being close together. The kind of places where "social distancing" is impossible. The worst areas are the ones where people are moving very fast in both directions. (curious, do people in London obey UK traffic rules, "driving" on the left hand instead of the right, when walking??) Here the lanes for walking mimic the cars, so youre always walking on the right and the opposite dirction is on your left.
Anyway, in Manhattan, especially in major subway transit points, there are huge numbers of people all walking through the same spaces, where its impossible to stay two meters apart.. (See "
Koyaanisqatsi" by Godfrey Reggio, a film from 1982 of fast motion photography for some great scenes taken in NYC.) During the morning or evening rush hour (both of which are actually two or three hours long) there are lots of people in places like multilevel stairways (some people out of breath and breathing deeply) and six way intersections, and long two way escalators underground. You cant adjust your position once you get on the escalator if somebody starts coughing, during rush hour there are people very close together. They have a small space in the middle between the up and down escalatators and each side's stairway is narrow, maybe 1M wide. These escalators are very long and whatever ventilation they have is of the "air blows in one end and out the other" variety. Thats no longer adequate.
That is a problem. they need more fresh ventilation in the middle of those long stairways and similar spaces. Instead of focusing their efforts on half-baked schemes that dont seem destined to work for their intended purpose, they should concentrate on the actual problem, the epidemic and mundane seeming problems like ventilation. Also they should stagger arrival times for workers.
To spread the commute hours out so the density is reduced. Specifically, making being in tight spaces and public transit, particularly, safer.
Because the main reason cities like New York and London work as well as they do is GREAT public transit.
People all getting private cars is a non starter, its just plainly impossible. Also many people dont like cell phones, and either dont have one or if they do, don't use it as these people who seem glued to cell phones do. I personally prefer reading when I am away from computers, things like physical newspapers and books. And I'm sure I am not the only one.
Accuracy matters a great deal. IMHO.
If they are using a technology that cannot be accurate enough according to its own developers, maybe its not the right technology!
The only alternative would be to use absolute location - GPS - which, as pointed out raises obvious privacy concerns. Also, I don't believe Apple allow for continuous location tracking on any app. I'm sure there will be a version that uses location tracking, but users would have to opt in, and I'm sure the powers-that-be are pretty hesitant because of an inevitable backlash.
The phrase "accurate enough" implies there is a known level of accuracy desired. There isn't. Even if somehow current smart phones had the ability to measure proximity to other phones with mm accuracy - at what point would it flag up "possible contagion contact" ? Would it be a sliding scale? Would that only be inside enclosed spaces? All the app really needs to do (for now) is to know whether or not the phones owner has been tested, and the result, and how often they have come into reasonably close proximity to other users that aren't in their household. I'm sure the devs working on this aren't making any kind of claims about efficacy - right now they're busy ironing out bugs and it will be an on-going experiment.
Yes and I doubt the developers themselves are epidemiologists. Any small degree of accuracy is better than the current situation. Even if it errs on the side of caution, generating some false positives, it will still mean fewer people, than now, will need to be isolated to control the spread.
Its technically impossible to get what they say they are trying to do, isnt that what the code comments seem to be saying?
GPS does not work in subways - at all. Not at al, nor does it work in most city buildings, at all. Outdoors, relative to indoors, there is practically no danger, maybe not no danger, but it is much much reduced. Even under the best of conditions, the only place GPS is going to be accurate is outdoors. Indoors, because the GPS antenna in a phone (typically a chip antenna on the PCB) is never going to be oriented as it should be, its always going to be next to this big thing that easts up most of the signals. (your body) So the location it calculates jumps around a lot unless you take care to make ot accurate. (I put my little tracking box in the "cd" pocket in my backpack and go to great lengths to check it that it hasnt shifted so the top is facing the sky. And when I go down in the subway I know from experience the GPS trace is going to be useless and vanish so I turn it off so as not to create a big jag between when I go into the subway and come out. Instead I get individual GPX files. (cheap non-RTK GPS logging produces various kinds of files, mine produces a "GPX file" the way its set up now. I use a program called GPSBabel to turn those traces into KML files.