0426: "Geohashing"

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Banksy
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Re: "Geohashing" discussion

Postby Banksy » Wed May 21, 2008 8:51 pm UTC

Yah I know I'm a failed geek for this, but can someone please tell me how to actually work this?
The idea sounds fantastic, but I've no idea how to work it
All this speak of algorithms and stuff makes me cry :'(

Thanks guys :)

I'll just go hand in my geek badge now...
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Re: "Geohashing" discussion

Postby miguelandres » Wed May 21, 2008 9:21 pm UTC

Only one person in these forums (other than me) has noticed this actually is Googleplex in Mountain View, California...

1600 Amphitheater Parkway, Mountain View, CA

http://maps.google.com/maps?f=q&hl=es&geocode=&q=N37.421542+W122.085589&ie=UTF8&t=h&ll=37.421759,-122.086118&spn=0.005947,0.010042&z=17&iwloc=addr

asteroid
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Re: "Geohashing" discussion

Postby asteroid » Wed May 21, 2008 9:49 pm UTC

the alt text--could it be referring to <a href="http://en.wikipedia.org/wiki/The_Game_%28treasure_hunt%29">The Game</a>? (Sorry if anyone brought this up on pages 2 or 3; i didn't have the patience to read them)

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Re: "Geohashing" discussion

Postby Luthen » Wed May 21, 2008 9:59 pm UTC

I thought it was a reference to Comic 238

Also the forum uses BBCode. Links are:

Code: Select all

[url]address[/url]
or
[url=address]words that'll appear[/url]
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Re: "Geohashing" discussion

Postby aquaone » Wed May 21, 2008 10:24 pm UTC

this is lame and silly... but was the best i could do with the limited access on my shell. :wink:
it will calculate a geohash for the current day by either a location (e.g. geohash.pl -l 'Seattle, WA') or by lat/lng (e.g. geohash.pl -L '57.696809,11.986084').
if anyone wants to extend it with Finance::QuoteHist and some more Date::Manip code, feel free.
i started to but couldn't get Finance::QuoteHist to work on my shell. :x

Code: Select all

#!/usr/bin/perl
use strict;
use Date::Manip qw( UnixDate );
use Digest::MD5 qw( md5_hex );
use Finance::Quote;
use Geo::GeoNames;
use Getopt::Std;
use Math::BigInt;

my( %opts, $dow, $lat, $lng, $md5 );
getopts('l:L:hv', \%opts);
# help
if( defined $opts{h} || ( ! defined $opts{l} && ! defined $opts{L} )) {
   usage();
   exit();
}

# date
my $date = UnixDate( 'today', '%Y-%m-%d' );

# dow lookup
my $q = Finance::Quote->new;
$q->timeout( 60 ); # override if you want to
my %quotes = $q->fetch( 'usa', '^DJI' );
my $dow = $quotes{'^DJI','open'} || '';
die "ERROR: DJI open could not be determined\n" if( ! $dow );
defined $opts{v} && print( "dow: $dow\n" );

# md5sum
$md5 = md5_hex( "$date-$dow" );
defined $opts{v} && print( "md5: $md5\n" );

# location
if( defined $opts{l} ) {
   my $geo = new Geo::GeoNames;
   my $res = $geo->search( q => $opts{l}, maxRows => 1 );
   ( $lat, $lng ) = ( $res->[0]->{lat}, $res->[0]->{lng} );
} elsif( defined $opts{L} ) {
   if( $opts{L} =~ /^(\d+)(\.\d+)?\,(\d+)(\.\d+)?$/ ) {
      ( $lat, $lng ) = ( $1, $3 );
   }
}
die "ERROR: could not determine lat/lng\n" if( ! $lat || ! $lng );
defined $opts{v} && print( "lat: $lat\nlong: $lng\n" );

# output
printf( "%d.%s,%d.%s\n", $lat, substr( Math::BigInt->new( "0x".substr $md5, 0, 16 ), 0, 5 ), $lng, substr
Math::BigInt->new( "0x".substr $md5, 16, 16 ), 0, 5 );
sub usage() {
   print <<EOF;
geohash.pl 0.3 - http://xkcd.org/426/
Calculates a geohash based on a given date and location
  -l 'loc'     uses the given location, e.g. 'Seattle, WA'
  -L 'lat,lng' uses the given latitude and longitude
  -h           display this text
  -v           verbose

created by aquaone <milkman\@eroticdairyproducts.com>
EOF
}

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botanydave
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Re: "Geohashing" discussion

Postby botanydave » Wed May 21, 2008 11:00 pm UTC

What Projection & Datum are used here?
I assume the datum is WGS84 (GPS standard). But depending on the map projection, I could be quite a ways away from the other xkcd fans standing about in a forest.

Demetrious
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Re: "Geohashing" discussion

Postby Demetrious » Thu May 22, 2008 12:03 am UTC

Just joined the forums, despite years of reading, just so I can take part in this meet-up (and actually socialize with people!) Anyone heading to the Florida area? I've got some coordinates locking me into an area close to Snake Bight in the Florida Everglades. So who's joining me! :lol:

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Re: "Geohashing" discussion

Postby seventoes » Thu May 22, 2008 12:16 am UTC

Ha.. mine is DIRECTLY in the middle of a small lake..

42.179467°, -83.861537°
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Re: "Geohashing" discussion

Postby Sungura » Thu May 22, 2008 12:30 am UTC

Okay...bit confused. I finally figured out I could click over to Michigan to get something within my area. But meet ups apparently are only for local time at 4:00 on Saturdays, so only the location it gives for Sat are meet up times, correct?
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Re: "Geohashing" discussion

Postby Luthen » Thu May 22, 2008 1:35 am UTC

Hmm... now its moved up to a dam that my granddad chief engineered (more or less) the construction of.
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Re: "Geohashing" discussion

Postby Daedalus » Thu May 22, 2008 1:47 am UTC

tarehart wrote:
AtG wrote:There is a limited number of hash outputs, 2^64. In 2^64+1 days there must be two equal outputs. You want proof of the opposite?


Oh.

Well, I still love the idea of geohashing.


2^64 days is about fifty quadrillion years. What's the estimate for the heat death of the universe again?

elyena
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Re: "Geohashing" discussion

Postby elyena » Thu May 22, 2008 2:10 am UTC

Anyone headed to 27231 Township Road 485, Calmar, AB T0C0V0?
Gogo Edmonton and area folks.

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Re: "Geohashing" discussion

Postby morpo » Thu May 22, 2008 2:34 am UTC

Ahh! Can't believe I'm graduating in a few days. To my fellow Cornellians - This Saturday, 4PM. Be there. If it's on Cayuga lake I'm swimming.

esmooths wrote:
ccccc wrote:First-post-inspire'd!

Ithaca, NY sits right in the center of its graticule. And the surrounding scenery is pretty nice. This seems like a good combination.



The day that the meeting point is at the top of the Cornell clocktower, I WILL go, no matter what.

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AtomicLlama
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Re: "Geohashing" discussion

Postby AtomicLlama » Thu May 22, 2008 2:37 am UTC

amysrabbitranch wrote:Okay...bit confused. I finally figured out I could click over to Michigan to get something within my area. But meet ups apparently are only for local time at 4:00 on Saturdays, so only the location it gives for Sat are meet up times, correct?


The meetup location for Saturday is actually based on Friday's Dow opening because the markets are closed on Saturday. So you can find the location for the Saturday meetup anytime after the market opens on Friday.

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Senefen
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Re: "Geohashing" discussion

Postby Senefen » Thu May 22, 2008 2:58 am UTC

Mine's in a national park halfway up the state (Victoria, Australia).
It's on a road at least, would be a good place to meet up if it wasn't so far. :(
Can I be bothered? Probably not.
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nyeguy
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Re: "Geohashing" discussion

Postby nyeguy » Thu May 22, 2008 3:01 am UTC

This works for the Denver Metro area well if you take the west half, though the area is divided down the middle. It will almost always produce results out in the mountains, often in South Park.
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Re: "Geohashing" discussion

Postby martinultima » Thu May 22, 2008 3:11 am UTC

Interesting concept - I wonder what kind of variations (and outright abuses) we can come up with?

I propose we forward this to the Debian people - should provide a much more secure way to generate SSL keys ;)
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Re: "Geohashing" discussion

Postby 1 1 2 3 5 8 13 21 » Thu May 22, 2008 3:25 am UTC

Okay, considering the various flaws:

1) MD5 is insecure. Horribly insecure. Well, for this application it doesn't really matter, but we're GEEKS, DAMNIT. Insecure doesn't cut it!
2) The Dow Jones is volatile, but provides entropy only 5 days a week, meaning that Sunday's Dow Jones opening would be known Thursday night (As Thursday's closing would be Friday's opening, and the NYSE not opening on the weekends, and the date is known in advance), giving a malicious prankster time to prepare. UNACCEPTABLE!

Proposed revision:

Entropy: Date in ISO8601 format: IE February 6, 1984 would be 1984-2-6
High/Low temperature of NYC (Specifically, La Guardia Airport) for the previous day in Fahrenheit: EG 85/59
Sunrise/Sunset for NYC the CURRENT day: EG: 5:33,20:12
Separate each entropy addition with a semicolon.

Example feed into the hash algo, using examples given: 1984-2-6;85/59;5:33,20:12

The formatting of the entropy is quite vital, as using different standards would result in divergent meeting places.

The concept is interesting, but without additional entropy, is flawed as it gives people meeting on Sundays exposure to undue risk of malicious pranksters. The window is significantly reduced with the addition of more entropy.

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Re: "Geohashing" discussion

Postby Archangel » Thu May 22, 2008 3:26 am UTC

Love the concept. Pity it doesn't always work very well around here because there's too much water.
Also, it covers quite a large area; would sometimes be quite a mission to get to the meetup point.

I don't think the web-based finder thing mentioned in the comic is quite working properly for locations in the southern hemisphere either. Looks like it's scrolling vertically the wrong way...

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Re: "Geohashing" discussion

Postby 1 1 2 3 5 8 13 21 » Thu May 22, 2008 3:36 am UTC

martinultima wrote:Interesting concept - I wonder what kind of variations (and outright abuses) we can come up with?

I propose we forward this to the Debian people - should provide a much more secure way to generate SSL keys ;)


As I outlined in my post, I alluded to an abuse... predicting Sunday's meeting place on Thursday night, head out there, and prepare some 'surprises'. Imagine surrounding the area with military-grade stink-bombs, and igniting them when a group gathers? Or just burying a couple of fish and eggs, for the less motivated... by Sunday, the smell would be particularly rank. Set up a fluidized sand pit. Et cetera.

ToastyKen
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Re: "Geohashing" discussion

Postby ToastyKen » Thu May 22, 2008 3:41 am UTC

Has anyone noticed that Randall has taken a rather pessimistic view of the market? He's expecting the Dow to tumble over 2000 points by Friday morning. :P

In fact, the last time the Dow opened that low was on November 2, 2005! I wonder if that date has any significance?

3-Nov-05 10,470.49
2-Nov-05 10,406.29

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Re: "Geohashing" discussion

Postby tradiuz » Thu May 22, 2008 4:23 am UTC

ToastyKen wrote:Has anyone noticed that Randall has taken a rather pessimistic view of the market? He's expecting the Dow to tumble over 2000 points by Friday morning. :P

In fact, the last time the Dow opened that low was on November 2, 2005! I wonder if that date has any significance?

3-Nov-05 10,470.49
2-Nov-05 10,406.29


Did you notice that the date in the comic is 2005?
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strix99
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Re: "Geohashing" discussion

Postby strix99 » Thu May 22, 2008 4:29 am UTC

Re: "Geohashing" discussion

Postby ToastyKen on Thu May 22, 2008 3:41 am UTC
Has anyone noticed that Randall has taken a rather pessimistic view of the market? He's expecting the Dow to tumble over 2000 points by Friday morning. :P

In fact, the last time the Dow opened that low was on November 2, 2005! I wonder if that date has any significance?


I think your missing that the date that was used in this comic is May 26th 2005.

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Re: "Geohashing" discussion

Postby Avram » Thu May 22, 2008 5:05 am UTC

I hate Alberta.

All the locations I've looked at are somewhere out in the endless stretches of farmland. How exciting.

EDIT: And to the people complaining about hashing economic data, here's a suggestion: take the day's date in 8-digit form. Let the resulting number be x. Then, hash an agreed-upon number (the more you choose, the less the algorithm repeats) of sequential digits of pi, beginning from pi's xth digit (and continuing up to x+8th).

Although that would allow us to predict future meetup locations, which of course would not be as much fun.

rheyns
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Re: "Geohashing" discussion

Postby rheyns » Thu May 22, 2008 5:29 am UTC

This is a very fun idea, and since the GooglePlex is less than a mile from my house I may just show up this Saturday :-P

One small problem though, when I do:

Code: Select all

echo "2005-05-26-10458.68" | md5sum

on my system I get

Code: Select all

357e5cac889681628fdd754c1a235919

which doesn't match the comic. Could someone enlighten me if I'm doing it wrong?

Now I know the Googleplex is just a convenient example but for some reason this still bothers me. Guess I was expecting honesty in nerddom or something.

/Still an awesome comic
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Re: "Geohashing" discussion

Postby bluesheep » Thu May 22, 2008 5:34 am UTC

Glad to see there are some seattle-ites here, other forums I dabble in never have any.

I'd happy to join in a few saturdays this summer. Not this saturday though.
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Re: "Geohashing" discussion

Postby muffin of doom » Thu May 22, 2008 5:54 am UTC

Too bad I live on an island. I tried every date for the past month, and only one of them produced a location that was not in the middle of the ocean. (May 11 would have been on a golf course.) Oh well, I doubt there are any other xkcd readers around here anyway. :(

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Re: "Geohashing" discussion

Postby phlip » Thu May 22, 2008 5:57 am UTC

rheyns wrote:One small problem though, when I do:

Code: Select all

echo "2005-05-26-10458.68" | md5sum

on my system I get

Code: Select all

357e5cac889681628fdd754c1a235919

which doesn't match the comic. Could someone enlighten me if I'm doing it wrong?

Try this:

Code: Select all

echo -n "2005-05-26-10458.68" | md5sum

That gives me the expected result.

What you're doing is taking the MD5 of "2005-05-26-10458.68\n".

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enum ಠ_ಠ {°□°╰=1, °Д°╰, ಠ益ಠ╰};
void ┻━┻︵​╰(ಠ_ಠ ⚠) {exit((int)⚠);}
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virgletati
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Re: "Geohashing" discussion

Postby virgletati » Thu May 22, 2008 6:45 am UTC

I'm also a little confused; using the tool on http://xkcd.com/geohashing for the date on the comic, I got:
http://irc.peeron.com/xkcd/map/map.html?date=2005-05-26&lat=37&long=-123&zoom=8&abs=1
but that is clearly different from the position in the comic, a rather lovely spot in "golden gate national recreation area": http://maps.google.com/maps?f=q&hl=en&geocode=&q=37.857713,+-122.544544&ie=UTF8&t=h&z=16&iwloc=addr

I don't understand how miguelandres got his location!

Interestingly, my computer rounds a little differently from Randall's, apparently, so I got the decimal conversion to be (37.857713, -122.544543) instead of (37.857713, -122.544544). However, this is exactly the same spot in google maps.

Also I noticed that in order to get the same md5 hash, you need to include the dashes in the date as well as between the date and the Dow opening. I tried playing around with the hash and this doesn't seem to be the source of the disparity between the tool and the comic, but I just thought it was a little unintuitive.

By the way, the Dow open on day N is totally not the same as the close on day N-1, from http://finance.google.com/finance/histo ... startdate= (the only part of the perl script for the tool I *can* read).

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Re: "Geohashing" discussion

Postby lukewarm » Thu May 22, 2008 7:47 am UTC

nyeguy wrote:This works for the Denver Metro area well if you take the west half, though the area is divided down the middle. It will almost always produce results out in the mountains, often in South Park.


Having a meetup location somewhere in South Park would be AMAZING!

= hash chaser

Ozzah
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Re: "Geohashing" discussion

Postby Ozzah » Thu May 22, 2008 9:47 am UTC

This is an interesting idea ... I like it.
Except that about 3/5 of the 1° box I live in is in water, so I have a large chance of not being able to swim that far.
And that when I enter some dates e.g. "2008-05-22" I get the response: "Market data is not available for 2008-05-22" and I'm not really sure what to make of it. :(

Other than that, it's cool! :)

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Re: "Geohashing" discussion

Postby grefab » Thu May 22, 2008 11:20 am UTC

I played around with LaTeX this night and modified the algorithm to place the points in a circle (with the start as center) rather than within a rectangle, just because I like circles more and thought this would be fairer for the surrounding area. :) I know this would be much nicer with graphics, but I didn't had the leisure to play with tikz.

Don't take it seriously, I did it to avoid studying for my next exam... :(

so long,

Gregor
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Vanguard
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Re: "Geohashing" discussion

Postby Vanguard » Thu May 22, 2008 11:31 am UTC

I figured this was a play on words on Geocaching but...

I don't get it.
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ikkleste
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Re: "Geohashing" discussion

Postby ikkleste » Thu May 22, 2008 11:45 am UTC

Daedalus wrote:
tarehart wrote:
AtG wrote:There is a limited number of hash outputs, 2^64. In 2^64+1 days there must be two equal outputs. You want proof of the opposite?


Oh.

Well, I still love the idea of geohashing.


2^64 days is about fifty quadrillion years. What's the estimate for the heat death of the universe again?


on top of that the hash outputs are already in significant excess of the number of unique locations with in a degree square, even by the equator (where the degree square fields are largest) you've still only got 1.2 x 1010 unique square meter locations (which i'm sure is more than accurate enough for any meet/adventure). This means that there are approx 1.5 billion hash values/m2.

You are going to start revisiting locations long before hash values repeat.

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Re: "Geohashing" discussion

Postby Luthen » Thu May 22, 2008 12:12 pm UTC

Only if the Dow is truly random, it is only likely to jump a certain amount in any day and there's a pretty high chance that over a few months it open with same value twice. Admittedly, it would have to do so on two Fridays to effect the randomness of the hash.
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amorya
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Re: "Geohashing" discussion

Postby amorya » Thu May 22, 2008 12:26 pm UTC

So, we need to combine the idea with this.

For example, this Saturday I'll be at 52.284247,-1.521596. By cunning manipulation of stocks I can induce many other XKCDers to turn up too :)

Amorya

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Re: "Geohashing" discussion

Postby One Thousand Words » Thu May 22, 2008 12:34 pm UTC

Annoyingly I live just to the west of the Greenwich Meridian [Cambridge UK], so if the location is right on the east side of my graticule (as it was yesterday), its all the way to the west of the one next door.

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Re: "Geohashing" discussion

Postby spartagus » Thu May 22, 2008 1:22 pm UTC

Today it looks like i better get my scuba gear ready, the Atlantic ocean is cold this time of year!
I plugged in my birth date and got a spot very close the stable I ride at. That's a little creepy.

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Re: "Geohashing" discussion

Postby Pixel » Thu May 22, 2008 3:46 pm UTC

I'm afraid this may ruin my last bits of resolve against getting a GPS for my car. I think it says something about me that "I can use it to stop getting lost, find more optimal routes places(saving gas), and not have to depend on printing out google maps" was not enough reason to get one, but "I can use it to find a randomly generated lat/long coordinate from a comic!" is.

I'm thinking this TomTom 130.
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Re: "Geohashing" discussion

Postby Random832 » Thu May 22, 2008 6:04 pm UTC

grefab wrote:I played around with LaTeX this night and modified the algorithm to place the points in a circle (with the start as center) rather than within a rectangle, just because I like circles more and thought this would be fairer for the surrounding area. :) I know this would be much nicer with graphics, but I didn't had the leisure to play with tikz.

Don't take it seriously, I did it to avoid studying for my next exam... :(

so long,

Gregor


It needs to be possible for two different starting points to result in the same answer, or it’s useless for meetups – did you consider this? (I can’t tell if your algorithm does this).

Choosing the nearest point (of your calculated point plus or minus one degree in either direction) would give an end-result domain that is centered on your starting point whilst allowing the same meetup point to be selected by other people.

I haven’t verified that this holds true for the vicinity of the prime meridian, 180°, or the equator.
Last edited by Random832 on Thu May 22, 2008 8:00 pm UTC, edited 2 times in total.


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