Talk:Air geohash achievement

Removed the kite section, due to the availability of the Geohash By Proxy achievement. --Pardey 07:04, 20 October 2008 (UTC)

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)