5 ms·

Interesting to note that the removal of selective availability enabled the creation of Geocaching ( https://en.wikipedia.org/wiki/Geocaching#History https://en.

by tomerv 5y ago

Interesting to note that the removal of selective availability enabled the creation of Geocaching ( https://en.wikipedia.org/wiki/Geocaching#History https://en.wikipedia.org/wiki/Geocaching#History ).

yborg 5y ago
It also enabled the modern mobile navigation industry. I was working on automotive navigation systems in the early 90s and SA was a killer for the product, options were various dead-reckoning and inertial sensors or differential GPS, both of which ended up being cost-prohibitive. But you can't do usable route guidance with a 100m CEP in an urban area.
- londons_explore 5y ago
  With modern high powered CPU's, more detailed maps, and particle filters (which require all that cpu), dead reckoning has become much more viable. I suspect you could go hours driving round a city with the GPS and WiFi location turned off before losing your position - simple wheel speed, gyro and compass is sufficient for most stuff.
  - NickNameNick 5y ago
    You'd also need to account for slope.
    - seanp2k2 5y ago
      I’ll be overjoyed the day that the compass in the vehicle can tell my phone what direction the vehicle is pointed to avoid making a left instead of a right out of a driveway. Yes, there are solutions to these problems in theory, but in real-world application today they’re still pretty lame / inaccurate, and the solutions still seem far away (try getting a few auto mfgs to agree to a standard way of communicating a compass heading to a phone over CarPlay or Android Auto)
      - michaelmrose 5y ago
        I've used a phone that didn't have a built in compass and one that does. The one that has an actual compass knows which direction I'm facing even without moving. The one that didn't would usually have no idea until I started moving. They make external GPS units that plug into your car and connect to your phone wirelessly for example Garmin GLO that are supposed to improve accuracy although I haven't used one myself and thus can't vouch for it.
        londons_explore 5y ago
        The built in compass in a phone is pretty inaccurate for driving because it can't compensate for the unknown shape of the body shell of the car it's in.
    - hunter2_ 5y ago
      When turn-by-turn directions specify traveling 1 mile down a very steep grade, do they mean 1 mile along the slope, or 1 mile along a flattened map? Only the former would match the car's odometer, of course.
  - exikyut 5y ago
    Hmmm. What about the sensors on my phone? For a while now I've wanted to know my realtime speed in the underground sections of the local rail/metro network. I suspect the most accurate measurements would be done using wideband SDR, iff I were able to acquire absolute position references for the signals I was seeing. Not likely, especially for something I might like to let others play with and/or generalize. Everywhere I read about the subject the general consensus is that using accelerometer and gyro data from the average phone is a fool's errand. I have zero experience with the field so I wouldn't know if failure was incorrect signal processing or just had sensors.
    - londons_explore 5y ago
      Without wheel speed sensors, distance and speed errors quickly accumulate. With a particle filter and enough computation, that error can be eliminated after the fact. Ie. At the time you won't know where you are, but after you get out of the metro and the particle filter reconverged you'll know where you were with more accuracy at some point in the past.
      - exikyut 5y ago
        Ah. I see. Thanks very much for that insight - so that's why it's possible, but not generally interesting and/or widely pursued.
askvictor 5y ago
There were already workarounds in place before they switched off SA - the introduced error was consistent within a given area, so provided you had a fixed location that broadcast its coordinates, you could correct for the error. I believe there were products and possibly even standards that did all of this; would have been even easier in today's world of mobile internet. I have suspicions that this was a large reason for disabling SA - your enemy can work around it, so it's not much use, but if you get your enemy hooked on it without the work-around, you can turn SA back on in a war situation.
- seanp2k2 5y ago
  Also, WAAS https://www8.garmin.com/aboutGPS/waas.html https://www8.garmin.com/aboutGPS/waas.html
deleted 5y ago
[deleted]

by tomerv 5y ago

yborg 5y ago

It also enabled the modern mobile navigation industry. I was working on automotive navigation systems in the early 90s and SA was a killer for the product, options were various dead-reckoning and inertial sensors or differential GPS, both of which ended up being cost-prohibitive. But you can't do usable route guidance with a 100m CEP in an urban area.

londons_explore 5y ago
With modern high powered CPU's, more detailed maps, and particle filters (which require all that cpu), dead reckoning has become much more viable. I suspect you could go hours driving round a city with the GPS and WiFi location turned off before losing your position - simple wheel speed, gyro and compass is sufficient for most stuff.
- NickNameNick 5y ago
  You'd also need to account for slope.
  - seanp2k2 5y ago
    I’ll be overjoyed the day that the compass in the vehicle can tell my phone what direction the vehicle is pointed to avoid making a left instead of a right out of a driveway. Yes, there are solutions to these problems in theory, but in real-world application today they’re still pretty lame / inaccurate, and the solutions still seem far away (try getting a few auto mfgs to agree to a standard way of communicating a compass heading to a phone over CarPlay or Android Auto)
    - michaelmrose 5y ago
      I've used a phone that didn't have a built in compass and one that does. The one that has an actual compass knows which direction I'm facing even without moving. The one that didn't would usually have no idea until I started moving. They make external GPS units that plug into your car and connect to your phone wirelessly for example Garmin GLO that are supposed to improve accuracy although I haven't used one myself and thus can't vouch for it.
      - londons_explore 5y ago
        The built in compass in a phone is pretty inaccurate for driving because it can't compensate for the unknown shape of the body shell of the car it's in.
  - hunter2_ 5y ago
    When turn-by-turn directions specify traveling 1 mile down a very steep grade, do they mean 1 mile along the slope, or 1 mile along a flattened map? Only the former would match the car's odometer, of course.
- exikyut 5y ago
  Hmmm. What about the sensors on my phone? For a while now I've wanted to know my realtime speed in the underground sections of the local rail/metro network. I suspect the most accurate measurements would be done using wideband SDR, iff I were able to acquire absolute position references for the signals I was seeing. Not likely, especially for something I might like to let others play with and/or generalize. Everywhere I read about the subject the general consensus is that using accelerometer and gyro data from the average phone is a fool's errand. I have zero experience with the field so I wouldn't know if failure was incorrect signal processing or just had sensors.
  - londons_explore 5y ago
    Without wheel speed sensors, distance and speed errors quickly accumulate. With a particle filter and enough computation, that error can be eliminated after the fact. Ie. At the time you won't know where you are, but after you get out of the metro and the particle filter reconverged you'll know where you were with more accuracy at some point in the past.
    - exikyut 5y ago
      Ah. I see. Thanks very much for that insight - so that's why it's possible, but not generally interesting and/or widely pursued.

askvictor 5y ago

There were already workarounds in place before they switched off SA - the introduced error was consistent within a given area, so provided you had a fixed location that broadcast its coordinates, you could correct for the error. I believe there were products and possibly even standards that did all of this; would have been even easier in today's world of mobile internet. I have suspicions that this was a large reason for disabling SA - your enemy can work around it, so it's not much use, but if you get your enemy hooked on it without the work-around, you can turn SA back on in a war situation.

seanp2k2 5y ago
Also, WAAS https://www8.garmin.com/aboutGPS/waas.html https://www8.garmin.com/aboutGPS/waas.html

deleted 5y ago

[deleted]