Talk:Air geohash achievement
Distance allowed for valid expedition
I just tried to figure out how near I have to be to the hashpoint while flying, using the 10 arc second rule. While doing that, I read Robyn's calculations on 2008-10-16 59 -122 and I think there is an error/misinterpretation by whoever first said "10 arc seconds". To get the 300 metre radius, Robyn took 10 arc seconds of the world's radius/circumference (6370 km and 40000 km resp.); But this means the "coordinates reached" radius neglects altitude above sea/ground level: It is 309m while flying at an altitude of 1 metre above sea level and only half a metre more while flying in a passenger plane at an altitude of 10km. I don't think that's what has been intended while creating the achievement. On the other hand, when starting counting from ground level, 10 arc seconds are about 0.5 centimetres for every 1 kilometre altitude, and that's not possible to achieve. I think we should change the requirement to "percentage of altitude", but how large should this percentage be? For a remotely controlled device, 1 metre at an altitude of 10 metres above ground should be possible with a few tries, this would be 10% and give 1 kilometre for a passenger plane flying at 10 kilometres. Or a larger percentage (20%) up to a certain altitude (1km / 1 mile...), and less above that. Please give your opinion. - Danatar 11:31, 9 November 2008 (UTC)
- I understood the "ten arc seconds" rule to mean within ten seconds of latitude and ten seconds of longitude as displayed on my cockpit GPS. That requires some precision in flying, and GREAT precision in camera clicking. Most of my air hashes are eight or nine seconds out in latitude or longitude. I don't see any sense in making the precision vary with the altitude, because it is no harder to fly a straight line at any given altitude. If there were to be a variation dependent on aircraft parameters, it should be on speed, because a pilot going 100 kts in a Cessna has more time to click the camera to capture the point than someone going 0.8 Mach.
- My 300 metre radius was calculated like this: One degree of latitude is 60 nautical miles. Therefore one minute of latitude is one nautical mile, a.k.a. 6000 feet. Ten seconds is one sixth of a minute, so 1000'. And that's about 300 m. I was flying east-west lines, so I was guaranteed to be at the exact second of longitude of any point, therefore the latitude would be the only offset. The maximum altitude for an airplane above the surface of the Earth would be about ten kilometres (I personally rarely fly over three). I haven't done the math, but that altitude is negligible (less than 0.2%) compared to the radius of the Earth, so the size of the area that is within 10 seconds doesn't really change with altitude.
- I think the current rule is fair: not too easy, not too hard. I have documented one or two missed geohashes, but there have been others. I'm in no way guaranteed to get a point even if it's right in front of me. It would be easier for a private pilot in a rented C150 who could drop the flaps and approach the point at 60 knots, and then turn around and try again if the first attempt were unsuccessful, especially if he had a buddy to work the camera.
- Perhaps the term "arc seconds" is just a misunderstanding. -Robyn 17:17, 9 November 2008 (UTC)
Would a FlightAware tracklog and an airline receipt or boarding pass be sufficient proof? While glancing at these for a commercial flight that I was a passenger on, I noticed that I passed within 2 miles of two different geohashes within the same flight. It's not unreasonable to think that a well-traveled person could check this for all of their flights and then find that they had snagged themselves an air geohash. Sure, it's not as hard as flying your own plane, but luck counts for something, right? Heck, if you wanted to pay for the old tracklogs, you might be able to get evidence of someone achieving a geohash _before_ geohashing was invented! - ErWenn ??:??, 25 November 2009 (UTC) (forgot to sign this when I posted it)
- I just had a look at the FlightAware tracklogs and there are only 2 decimals shown, i.e. the distance is rounded to about 1 km with a 500 m accuracy. That's more than 10 arc seconds (16 north-south, >20 east-west), so I think it's not accurate enough.
- In general, being a passenger on a commercial flight is perfectly acceptable. But I think you need to bring your own tracklogger with a better accuracy (and I recommend more than one acquisition per minute). Or you can
make the pilotask the pilot to fly through multiple hashpoints and take pictures of the plane's GPS. - Danatar 11:17, 26 November 2009 (UTC)
- Good point. I guess I'll have to keep my GPSr out and sit next to the window (couldn't keep a lock on the satellites from seat two). On a related note, I was thinking about the difficulty involved in getting good evidence at high speeds and it occurs to me that there's a maximum amount of deviation possible in certain vehicles at certain speeds. So I think that evidence for speed, time, and location for two points on opposite sides of the geohash should count (or even evidence for velocity and location (including bearing) for one point, if it's close enough). The question would be how close to the geohash those points would have to be to count as proof. (We might also have to take into account turbulence shifts, but I don't know how significant that would be horizontally.) So if you had two data points 8.3 miles and one minute apart, and your plane had a maximum speed of 560mph, then even supposing the plane could change direction instantly, the furthest away from the midpoint between those two points you could get would be 2.13 miles. That's a pretty big distance, so I'd need either a better estimate, perhaps taking into account the turning radius, or more frequent data points. I'll think more about this... ErWenn 16:22, 26 November 2009 (UTC)
Restarting an old debate, but FlightAware's technology has increased since 2009. At least for the flight I checked, their tracklogs now have 4 digits shown, which I believe would be in accuracy. I assume this means that FlightAware hashes would now be kosher (with the required proof of course), correct? I didn't get one, but some other lucky geohasher might. -Haberdasher 17:31, 25 August 2012 (EDT)
- I just looked into this for myself, hoping to land an AirHash for my Thanksgiving trip to Boston. Indeed the FlightAware tracklogs now give 4 decimal places in degrees (still at 1 minute intervals). Ten seconds of arc is about 0.0003 degrees, so four places should be adequate. I was prepared to show a plot generated from the FlightAware data with the hashpoint coordinates overlaid, a scan of my boarding pass, and (for interest only) some photos shot out the window during the relevant part of the flight. Sadly, the plane did not go far enough east over Massachusetts Bay on its approach to Logan to let me claim success; I needed -70.8870 and the farthest east the southbound plane got was -70.9333. Given how effectively it has showed me that I did not reach the coordinates, I'd be willing to take it as adequate proof that someone else had. Mcbaneg (talk) 18:32, 30 November 2015 (EST)
- Sourcerer got lucky on a commercial flight over 2018-01-31 43 19. The expedition report explains things in more detail. I found it easy to get the evidence. My Garmin eTrex 20 updates the screen every second and I had configured it to allow screen grabs, clicking after each screen update. I got two grabs showing under 300 metres and about 10 grabs in total. Cruising speed is about 220 m/s. I was also able to load the GPX track into Google Earth. This confirmed the screen shots. Hashpoints go by every 10 to 15 minutes on a 737, 800. Even at mach 3 you'd have plenty of time to reporgram for the next hashpoint. The 300 or 310 metre rule draws a 600 or 620 metre stripe across the graticule. With equatorial graticules 111km wide, there's about 0.5% chance of hitting a hashpoint with a blindfolded pilot. Nearer the poles, it gets easier. Regular flyers should catch hashpoints quite frequently. Sitting by the window helps a lot with GPS lock. Avoid the barometric altimeter feature in the GPSr or you'll get the cabin pressure instead of true altitude. --Sourcerer (talk) 12:24, 5 February 2018 (UTC)