0426: "Geohashing"

This forum is for the individual discussion thread that goes with each new comic.

Moderators: Moderators General, Prelates, Magistrates

Kleptonis
Posts: 4
Joined: Wed May 16, 2007 10:40 am UTC

Re: "Geohashing" discussion

Postby Kleptonis » Thu May 22, 2008 6:12 pm UTC

Yesterday's geohash took me to my high school. Convenient? :?

1 1 2 3 5 8 13 21
Posts: 13
Joined: Fri May 16, 2008 7:29 pm UTC

Re: "Geohashing" discussion

Postby 1 1 2 3 5 8 13 21 » Thu May 22, 2008 7:35 pm UTC

Luthen wrote: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.

Except that doesn't matter. The dates of the two identical openings will still be different, and thus the hash will come out different.

Pyrotix
Posts: 51
Joined: Wed Sep 19, 2007 2:38 pm UTC

Re: "Geohashing" discussion

Postby Pyrotix » Thu May 22, 2008 8:54 pm UTC

You just use the function to append something to the end of your latitude longitude right?

Anyone in the downtown Toronto area planning on going to Saturdays location? (if its not in Lake Ontario)

miguelandres
Posts: 2
Joined: Wed May 21, 2008 9:18 pm UTC

Re: "Geohashing" discussion

Postby miguelandres » Thu May 22, 2008 9:43 pm UTC

virgletati wrote: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.


Hmm I got it from the original location, put it in google maps and voilà. But the result from the geohashing got me to that middle of nowhere place you showed.

However, I disagree with you, the md5 hash in my Mac doesn't say the same as in the comic, and I tried some different options.

Code: Select all

HaruhiMacBook:~ miguelandres$ echo "2005-05-26-10458.68" | md5sum
357e5cac889681628fdd754c1a235919  -
HaruhiMacBook:~ miguelandres$ echo "2008-05-26-10458.68" | md5sum
d1bcdda27931f7b0a72aa766fd489287  -
HaruhiMacBook:~ miguelandres$ echo "2005-05-2610458.68" | md5sum
f7d42acd94fdb787b005596031100f8b  -
HaruhiMacBook:~ miguelandres$ echo "2008-05-2610458.68" | md5sum
04c40936f5f0faf1c4c3ac88f8469990  -

User avatar
phlip
Restorer of Worlds
Posts: 7573
Joined: Sat Sep 23, 2006 3:56 am UTC
Location: Australia
Contact:

Re: "Geohashing" discussion

Postby phlip » Thu May 22, 2008 10:27 pm UTC

miguelandres wrote:the md5 hash in my Mac doesn't say the same as in the comic, and I tried some different options.

phlip wrote: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".

Code: Select all

enum ಠ_ಠ {°□°╰=1, °Д°╰, ಠ益ಠ╰};
void ┻━┻︵​╰(ಠ_ಠ ⚠) {exit((int)⚠);}
[he/him/his]

Thalagyrt
Posts: 37
Joined: Wed May 07, 2008 2:11 pm UTC

Re: "Geohashing" discussion

Postby Thalagyrt » Thu May 22, 2008 10:49 pm UTC

Miami's meetup location for today lies (almost) directly on the Florida Turnpike. 8)

User avatar
Luthen
Posts: 2021
Joined: Thu Feb 21, 2008 6:42 am UTC
Location: Dealing with xkcdian immigration
Contact:

Re: "Geohashing" discussion

Postby Luthen » Thu May 22, 2008 11:25 pm UTC

1 1 2 3 5 8 13 21 wrote:
Luthen wrote: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.

Except that doesn't matter. The dates of the two identical openings will still be different, and thus the hash will come out different.

Yes, you're right, I'm an idiot.

In other news, my one for today is on a freeway on-ramp.
My fancy new blog Image I am not a vampire! Image PM my location for a prize!*

rnew: ALL GLORY TO THE HYPNOAVATAR!
*Terms + conditions changeable

grefab
Posts: 2
Joined: Thu May 22, 2008 2:10 am UTC

Re: "Geohashing" discussion

Postby grefab » Fri May 23, 2008 12:42 am UTC

Random832 wrote:
grefab wrote:...modified the algorithm to place the points in a circle (with the start as center) rather than within a rectangle, ...

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).

It actually doesn't. It simply calculates a position somwhere within a circle-shaped surrounding around a starting point. My intent was to create a circle-shaped area, because in my graticlue I live in a corner, so that with high probability a reachable point means a lot of driving. :)

Of cource this isn't the best method for creating meetup-points, but one can modify it to accomplish this (e.g. by rounding the coordinates), but that would result in the same problem.

Random832
Posts: 2525
Joined: Wed Oct 10, 2007 4:38 pm UTC

Re: "Geohashing" discussion

Postby Random832 » Fri May 23, 2008 1:46 am UTC

grefab wrote:
Random832 wrote:
grefab wrote:...modified the algorithm to place the points in a circle (with the start as center) rather than within a rectangle, ...

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).

It actually doesn't. It simply calculates a position somwhere within a circle-shaped surrounding around a starting point. My intent was to create a circle-shaped area, because in my graticlue I live in a corner, so that with high probability a reachable point means a lot of driving. :)

Of cource this isn't the best method for creating meetup-points, but one can modify it to accomplish this (e.g. by rounding the coordinates), but that would result in the same problem.


Try my suggested algorithm: Calculate the one for your own graticule and the eight adjacent spaces and pick the closest one. That way it’ll match with the points everyone else is getting.

Note: You'll actually only need three adjacent spaces, the ones that are closer to your start point.

User avatar
IW4
Posts: 19
Joined: Fri Mar 14, 2008 4:09 am UTC

Re: "Geohashing" discussion

Postby IW4 » Fri May 23, 2008 1:35 pm UTC

So now that the NYSE has opened for the day, the calculating site isn't loading. I'm absolutely not surprised; too many people like me with too much time on their hands (but not enough to manually hash the index) and not enough to do on a Saturday night.

Now if only I weren't in Montana tomorrow.

User avatar
phlip
Restorer of Worlds
Posts: 7573
Joined: Sat Sep 23, 2006 3:56 am UTC
Location: Australia
Contact:

Re: "Geohashing" discussion

Postby phlip » Fri May 23, 2008 1:53 pm UTC

IW4 wrote:(but not enough to manually hash the index)

Code: Select all

phlip@boris:~$ echo -n 2008-05-24-12620.90 | md5sum | cut -c 1-16,17-32 --output-delimiter=' '
206c010b0db51d78 8c2b217d762e9546

So the magic offsets this Saturday are 0.126648..., 0.547533... (decimal)

Code: Select all

enum ಠ_ಠ {°□°╰=1, °Д°╰, ಠ益ಠ╰};
void ┻━┻︵​╰(ಠ_ಠ ⚠) {exit((int)⚠);}
[he/him/his]

sexybobo
Posts: 6
Joined: Wed Oct 17, 2007 9:34 pm UTC

Re: "Geohashing" discussion

Postby sexybobo » Fri May 23, 2008 2:09 pm UTC

* 39.126648°, -94.547534°
Any one in KC going to be there it looks like it is in some ones back yard but i will be on the street in front at 4pm tomorrow.

User avatar
SimonBob
Posts: 34
Joined: Tue May 20, 2008 8:13 pm UTC
Location: Ottawa, ON
Contact:

Re: "Geohashing" discussion

Postby SimonBob » Fri May 23, 2008 2:11 pm UTC

Holy guff -- very definitely going to be able to make it to tomorrow's Ottawa location, or at least as close as I can get to it on Melrose. It seems the Dow is cooperating nicely with the introductory weekend; hopefully the weather will do the same.
The Mammon Industry
Because it can't be art until the gods get the money.

teucer
Posts: 42
Joined: Wed Aug 08, 2007 4:28 pm UTC

Re: "Geohashing" discussion

Postby teucer » Fri May 23, 2008 2:40 pm UTC

SimonSwift wrote:Okay, but does anyone else actually live in Minnesota?

*crickets*


~Siswi


Yes. And in the most populous grid section of it, too.

Irritatingly, though, it's a 90-minute drive to the meetup for me, and I've got plans for a good chunk of the afternoon. I think I have to give it a miss. (Though, oddly, if I pretend to be in the northern suburbs, it gets closer. Still, I probably won't be there.)

User avatar
Miike
Posts: 107
Joined: Sun Feb 18, 2007 10:45 pm UTC
Location: Pittsburgh, PA
Contact:

Re: "Geohashing" discussion

Postby Miike » Fri May 23, 2008 3:08 pm UTC

So is there a reason the calculator is all over the place right now? It SHOULD just be using the start data but seems to be updating with the Dow every time...?

gumbo
Posts: 12
Joined: Mon Apr 07, 2008 4:29 pm UTC

Re: "Geohashing" discussion

Postby gumbo » Fri May 23, 2008 3:13 pm UTC

My Saturday is looking too busy to make a meetup, but it looks like a reasonable location based on my home address: a little north of Harper's Ferry, not far from the river, in what looks like somebody's farmland (but close enough to the road that a roadside meetup would work.)

Checking out the other 3 DC quadrants, the Baltimore one puts you in the middle of a residential neighborhood that looks full of big, expensive houses with swimming pools. Pool party!

The SW corner (which includes most of DC) puts you in farmland out in Virginia. The SE corner quadrant puts you in a big empty field that's probably somebody's farmland down in southern MD.

Aristocrates
Posts: 1
Joined: Fri May 23, 2008 3:21 pm UTC

Re: "Geohashing" discussion

Postby Aristocrates » Fri May 23, 2008 3:26 pm UTC

Regarding the map being all over the place: When I turned on the debugging info, I noticed that every time the Update button was clicked, one or more zeroes were added to the end of the Dow opening.

I'm thinking that because the Dow opening was a multiple of ten cents, 12620.9, the tool is trying to express it as 12620.90, and getting a bit confused.

I wonder if a similar bug would occur for an integer dollar amount.

User avatar
dharmamama
Posts: 64
Joined: Mon Nov 26, 2007 1:37 am UTC
Location: lower left side of each post

Re: "Geohashing" discussion

Postby dharmamama » Fri May 23, 2008 4:04 pm UTC

My meetup place is do-able, but it's race weekend, so traffic will be horrendous all day Saturday.

Any NASCAR fans here?

yeah, me neither.

bjh
Posts: 2
Joined: Fri May 23, 2008 5:54 pm UTC

Re: "Geohashing" discussion

Postby bjh » Fri May 23, 2008 6:15 pm UTC

Aristocrates wrote:Regarding the map being all over the place: When I turned on the debugging info, I noticed that every time the Update button was clicked, one or more zeroes were added to the end of the Dow opening.

And not only that, but the first run seems to have an extra zero (according to the debugging output).

I have not been able to get http://www.xkcd.com/geohashing to match the Saturday numbers of "0.126648..., 0.547533... (decimal)" mentioned in a previous reply. Does it work for anyone?

Mr. Pants
Posts: 2
Joined: Fri May 23, 2008 6:20 pm UTC

Re: "Geohashing" discussion

Postby Mr. Pants » Fri May 23, 2008 6:42 pm UTC

So, I slogged through the pages of "I don't get it", "My point is here", and "you should do it this way". Maybe some official erratum for international concerns are needed?

What I was hoping to find were some resources about local law and zoning. How do I know if a spot is legal? I know these concerns aren't congruent with the whimsy of xkcd, but I really don't like cops. With gas prices as there are, an added Trespassing Fine will blow the budget for sure.

User avatar
spotrh
Posts: 8
Joined: Mon Sep 24, 2007 2:02 am UTC
Location: Arlington, MA
Contact:

Re: "Geohashing" discussion

Postby spotrh » Fri May 23, 2008 7:00 pm UTC

Sadly, the Boston geohash for Saturday looks to be in someone's front yard, almost certainly private property.

tarehart
Posts: 7
Joined: Wed May 21, 2008 5:08 am UTC

Re: "Geohashing" discussion

Postby tarehart » Fri May 23, 2008 7:06 pm UTC

I just realized that the best game to bring on a geohashing excursion is bocce.

Mounky
Posts: 4
Joined: Wed Nov 07, 2007 8:19 pm UTC

Re: "Geohashing" discussion

Postby Mounky » Fri May 23, 2008 7:18 pm UTC

Every time I zoom in, out, move the map, or press the update button I get a comletely new meetup spot. Anyone else have this problem?

User avatar
sqrt(-1)<3pi
Posts: 28
Joined: Mon Feb 04, 2008 9:49 pm UTC

Re: "Geohashing" discussion

Postby sqrt(-1)<3pi » Fri May 23, 2008 7:43 pm UTC

Mounky wrote:Every time I zoom in, out, move the map, or press the update button I get a comletely new meetup spot. Anyone else have this problem?


I'm getting this problem today, but i wasnt yeterday or wednesday. I dunno, but i hope it's fixed soon so i can go on an adventure tomorrow!
public static String reCurse()
{
``````return "Damnit!" +reCurse();
}

[the 4th root of n]*([the previous number - 1] to the 4th)-(the product of the 2 numbers in brackets)=the answer to Life the Universe and Everything, where n is the page of my post in the intro thread

ccccc
Posts: 7
Joined: Wed May 21, 2008 7:13 am UTC
Location: Ithaca, NY

Re: "Geohashing" discussion

Postby ccccc » Fri May 23, 2008 9:37 pm UTC

Yes, this is an unfortunate time for things to suddenly stop working on the only centrally-located implementation we have... :(

Does anyone have the correct coordinates for today (i.e. for this Saturday)?

Edit: Can anyone independently confirm that these are correct (as was posted above)?
0.126648..., 0.547533...

Stefanwulf
Posts: 1
Joined: Fri May 23, 2008 4:28 pm UTC
Location: Washington, D.C.

Re: "Geohashing" discussion

Postby Stefanwulf » Fri May 23, 2008 9:46 pm UTC

gumbo wrote:The SW corner (which includes most of DC) puts you in farmland out in Virginia. The SE corner quadrant puts you in a big empty field that's probably somebody's farmland down in southern MD.


The SE corner of the DC area zones (only the southern two include the city proper) seems to be closer to a street than the SW one. The problem now is that I'm concerned that I'm looking at a different big empty field than other people, thanks to reports of the map's unreliability. If anyone else is in DC and planning on trying this tomorrow, I'm currently getting 38.400246°, -76.722772° for the SE zone, which hopefully matches with yours.

gandazgul
Posts: 3
Joined: Fri May 23, 2008 10:20 pm UTC

Re: "Geohashing" discussion

Postby gandazgul » Fri May 23, 2008 10:35 pm UTC

How are you guys transforming the hex number to decimal(float)?

using the calculator that comes standard with Ubuntu I get for today's ( MD5(2008-05-23-12620.90): 667694a9e6b55f07b90793d5d2eed3c7 ) hash:

hex = dec
0.667694A9E6B55F07 = 0.400246898
0.b90793d5d2eed3c7 = 0.722771873
like the ones here http://irc.peeron.com/xkcd/map/ : offset = 0.4002468981550087, 0.7227718731909889 :)

but... and here is my problem the PHP function hexdec() or base_convert() ignores the . in the hex strings and gives me some totally different numbers...

so... can you tell me how to do this? Randall, man, how did you do it? :)

thanks,

PS: I have set-up a Dow Jones Industrial Average opening price source here: http://sctree-it.sytes.net:50324/dow.php, I am getting the number from google's finance website. The url format complies with XKCD standard, ?yy=%Y&mm=%m&dd=%d&dbg=true, the last parameter shows the value of the variables in each step of the process, to get just the opening price don't include it. To get today's opening price don't pass any parameters... if you do pass parameters for today's date before 4:00pm is going to return yesterday's opening price.

My attempt at implementing a google map to calculate today's point and give you information about it is still under development and can be found here: http://sctree-it.sytes.net:50324/geohash.php, this one has the same parameters as dow.php. Hope you like it.

NOTE: this server is a server at home, I rarely turn it off so its very reliable but please don't abuse it... thank you. :)
Last edited by gandazgul on Sat May 24, 2008 2:36 am UTC, edited 1 time in total.

User avatar
Mitora
Posts: 156
Joined: Sun Apr 13, 2008 11:37 pm UTC

Re: "Geohashing" discussion

Postby Mitora » Fri May 23, 2008 10:58 pm UTC

Can someone figure out Hackensack NJs for me? Or NYC? I live in NY but NJ would be easier to find.
Image

grisson
Posts: 11
Joined: Tue Nov 13, 2007 7:36 pm UTC

Re: "Geohashing" discussion - A buglet, I think.

Postby grisson » Fri May 23, 2008 11:59 pm UTC

From the http://xkcd/geohashing page.
For Rock Hill SC on May 24:
Debug info from the screen the first time before clicking map:
Graticule: (34, -81) - (35, -80)

After entering 2008-05-24 and clicking map:
Graticule: (34, -82) - (35, -81)
and there is no pointer on the screen

After clicking update :
Graticule: (34, -82) - (35, -81)
Market open on 2008-05-24 = 12620.90
MD5(2008-05-24-12620.900): 3ae7c530ce1c202b485f276f80c3a53e
Split: 3ae7c530ce1c202b, 485f276f80c3a53e
offset = 0.23009903375178497, 0.28270193550339556
34.230099033751784 -81.2827019355034
Setting food link: http://local.google.com/maps?f=l&hl=en& ... &z=13&om=0

and there is a pointer on the screen, which I suspect is the real location but....
After clicking Update AGAIN!
Graticule: (34, -82) - (35, -81)
Market open on 2008-05-24 = 12620.9000
MD5(2008-05-24-12620.90000): a8b945c49dfd064088580bdbd455c24c
Split: a8b945c49dfd0640, 88580bdbd455c24c
offset = 0.6590770344755478, 0.532593480271621
34.65907703447555 -81.53259348027161
Setting food link: http://local.google.com/maps?f=l&hl=en& ... &z=13&om=0

I'm thinking this is a bug.

User avatar
Miike
Posts: 107
Joined: Sun Feb 18, 2007 10:45 pm UTC
Location: Pittsburgh, PA
Contact:

Re: "Geohashing" discussion

Postby Miike » Sat May 24, 2008 2:50 am UTC

tarehart wrote:I just realized that the best game to bring on a geohashing excursion is bocce.



Close. But if you're up to carrying it, croquet for the win!

Thalagyrt
Posts: 37
Joined: Wed May 07, 2008 2:11 pm UTC

Re: "Geohashing" discussion

Postby Thalagyrt » Sat May 24, 2008 4:21 am UTC

The Miami meet-up is in the middle of the water several miles west of Key Largo. :(

SocialSceneRepairman
Posts: 199
Joined: Sat May 24, 2008 4:17 am UTC

Re: "Geohashing" discussion

Postby SocialSceneRepairman » Sat May 24, 2008 4:27 am UTC

And for the all-important 42N, 71W...

Gaskill Cir., Hopedale, MA.

Get off 495 at exit 19 and go west on 109. Merge onto route 16 after what looks like about a mile and keep driving through the better part of Milford and Hopedale (four miles or so), until you see Hammond Rd. on your right. Go about half a mile and you'll see it on your right.

Since it looks like a residential street, it's probably best not to be more specific than that.

Takers?

User avatar
phlip
Restorer of Worlds
Posts: 7573
Joined: Sat Sep 23, 2006 3:56 am UTC
Location: Australia
Contact:

Re: "Geohashing" discussion

Postby phlip » Sat May 24, 2008 6:51 am UTC

gandazgul wrote:using the calculator that comes standard with Ubuntu I get for today's ( MD5(2008-05-23-12620.90): 667694a9e6b55f07b90793d5d2eed3c7 ) hash:

hex = dec
0.667694A9E6B55F07 = 0.400246898
0.b90793d5d2eed3c7 = 0.722771873
like the ones here http://irc.peeron.com/xkcd/map/ : offset = 0.4002468981550087, 0.7227718731909889 :)

Yep, these numbers are correct, for Friday. I posted the Saturday numbers above (I just double-checked them, they're still right). For completeness (since the DOW'll still have the same problematic value), the Sunday offsets are 0.941775, 0.182874.

Probably the easiest way to calculate the decimal fractions in PHP would be:

Code: Select all

hexdec($piece_of_MD5_string) / 0x10000000000000000

Code: Select all

enum ಠ_ಠ {°□°╰=1, °Д°╰, ಠ益ಠ╰};
void ┻━┻︵​╰(ಠ_ಠ ⚠) {exit((int)⚠);}
[he/him/his]

gandazgul
Posts: 3
Joined: Fri May 23, 2008 10:20 pm UTC

Re: "Geohashing" discussion

Postby gandazgul » Sat May 24, 2008 7:07 am UTC

phlip wrote:
gandazgul wrote:using the calculator that comes standard with Ubuntu I get for today's ( MD5(2008-05-23-12620.90): 667694a9e6b55f07b90793d5d2eed3c7 ) hash:

hex = dec
0.667694A9E6B55F07 = 0.400246898
0.b90793d5d2eed3c7 = 0.722771873
like the ones here http://irc.peeron.com/xkcd/map/ : offset = 0.4002468981550087, 0.7227718731909889 :)

Yep, these numbers are correct, for Friday. I posted the Saturday numbers above (I just double-checked them, they're still right). For completeness (since the DOW'll still have the same problematic value), the Sunday offsets are 0.941775, 0.182874.

Probably the easiest way to calculate the decimal fractions in PHP would be:

Code: Select all

hexdec(<16 digits of MD5 string>) / 0x10000000000000000


phlip, thanks a lot. I was doing it like this:

Code: Select all

for ($i = 1; $i <= 16; $i++)
{
   $lat_offset += intval(substr($md5, 16 - $i, 1), 16);
   $lon_offset += intval(substr($md5, 32 - $i, 1), 16);
   $lat_offset /= 16;
   $lon_offset /= 16;
}


I translated this from the JS code used here: http://irc.peeron.com/xkcd/map/xkcd.js and it works, but your way is cleaner :).

My implementation is going great. I also want to make a version that will map the point adding the offset to your complete coordinates, not just the int part. I think that way you will get closer points. For a group you can establish a source point that is fixed... like the integer coordinates... my aim with this is to "fix" the graticulates like the NY one that are half in the water.

What do you guys think?

User avatar
phlip
Restorer of Worlds
Posts: 7573
Joined: Sat Sep 23, 2006 3:56 am UTC
Location: Australia
Contact:

Re: "Geohashing" discussion

Postby phlip » Sat May 24, 2008 7:19 am UTC

gandazgul wrote:it works, but your way is cleaner :).

Well, my way assumes that the hex string is exactly 16 digits long. Your code is more generic... pretty easy to turn it onto something that would work for any length of string. Also, I'm not sure if mine would work in JS.
[edit] It looks like parseInt(md5stuff,16)/0x10000000000000000 does work in JS... at least in both IE6 and Firefox, which are the only ones I have access to...

gandazgul wrote:For a group you can establish a source point that is fixed...

Still, you'd lose one of the advantages of the current system, which is that two people who live close to one another can get the same meetup point, without any prior collaboration between the two (or, indeed, knowing the other even exists).

Code: Select all

enum ಠ_ಠ {°□°╰=1, °Д°╰, ಠ益ಠ╰};
void ┻━┻︵​╰(ಠ_ಠ ⚠) {exit((int)⚠);}
[he/him/his]

gandazgul
Posts: 3
Joined: Fri May 23, 2008 10:20 pm UTC

Re: "Geohashing" discussion

Postby gandazgul » Sat May 24, 2008 4:29 pm UTC

phlip wrote:[edit] It looks like parseInt(md5stuff,16)/0x10000000000000000 does work in JS... at least in both IE6 and Firefox, which are the only ones I have access to...


I'm keeping both :), yes you are right the for() can be worked for any length... nice to know for any projects in the future.

phlip wrote:
gandazgul wrote:For a group you can establish a source point that is fixed...

Still, you'd lose one of the advantages of the current system, which is that two people who live close to one another can get the same meetup point, without any prior collaboration between the two (or, indeed, knowing the other even exists).


hmmm... no... if you both use the same implementation and this implementation has fixed start points for cities you'll both get the same point without knowing each other... What I propose is to, in the cities or metropolitan areas, move the graticules to arbitrary positions so they fit the whole city or are completely inland. The NY city graticule for example is half water, half of the points are going to be in the Atlantic :) not a fun place to go (providing you don't have a boat). When you click the map, it recognizes those coordinates and instead uses a predetermined point that makes the graticule appear completely inland, and then it gives you the point for today, it will be the same point for all those who use this implementation. It's a small change to the original algorithm. if you can convince everybody to use it his way it's better still :)

NY is not alone by the way... San Francisco is half (diagonaly) in the Pacific, Long Beach is completely in the water, San Diego, The north of Chicago and Milwaukee are in the lake.

The other problem I think this is solving is division... NY and Philadelphia for example are completely divided, they fall in 4 graticules they should fall in one...

it's just a thought. :)

Doctor
Posts: 22
Joined: Mon Sep 24, 2007 6:41 pm UTC

Re: "Geohashing" discussion

Postby Doctor » Sat May 24, 2008 5:25 pm UTC

Randy,

Thank you for fulfilling my request for a tougher challenge for locating meetups. Extra thank you for making the meetups perpetual.

I also assume you know that I'm out of town today and again from Thursday till August, so I'm totally missing out till then. :(((((((

Any XKCDers willing to meet in Moscow region?

cwolves
Posts: 2
Joined: Sat May 24, 2008 5:35 pm UTC

Re: "Geohashing" discussion

Postby cwolves » Sat May 24, 2008 5:51 pm UTC

My proposed twerk for accounting for water:

Pull data from a coastline database, e.g.: http://rimmer.ngdc.noaa.gov/mgg/coast/getcoast.html. The best data they have seems to be 1-70,000 scale which is good enough. Check your calculated point against this and simply jump to the nearest coastline.

There's two problems with this, using this database anyway. First, the data they provide doesn't have any indication of which direction land is, it's a list of points making up the coastline but you have no way of knowing if the point you currently have is in the water or on land. Granted you can accurately guess this most of the time in the US by simply checking the longitude (<100, ocean is south-east, >100 ocean is west), but then you get bays, florida, other thin strips of land/water, etc.

Problem #2: this data doesn't seem to include lakes. Some larger ones, yes, but the San Jose meeting point is right next to a lake today and this data doesn't see that.

So I still like my idea, I just need better data to run it against :) Anyone know of a source?


As for cities, I like the idea submitted by someone else that you simply take the closest generated point to you. This makes the algorithm graticules more dependent on population centers and geographical features as opposed to "arbitrary" (lat/lon) lines. MOST of the time, everyone in a city will, this way, have the same meeting point. Granted, if you have two points that are equal distance from a city, it will depend on where in the city you are, but for cases pointed out where cities are bisected by two or more areas, there's much less of a problem. I don't think there's any way to completely guarantee that everyone in a given city will get the same point unless you manually define all the graticules, which is a horrible idea.

Eehk
Posts: 2
Joined: Sun May 25, 2008 4:26 am UTC
Location: Monroe, WA;Cannon Beach, OR
Contact:

Re: "Geohashing" discussion

Postby Eehk » Sun May 25, 2008 4:49 am UTC

This is my first post. It took Geohashing to finally get me signed up here, been a long time reader of the comic, and more recently, the blag.

I've just acquired a GPS receiver from my dad, and this sounds really fun. I'm in the Seattle block, and I see a bunch of other people are too on the wiki. I may try to get to some meet-ups over the summer. When fall rolls around I'll be in Cannon Beach, OR at school, which is going to have a ton of cool spots to explore along the coast. Awesome.

Not sure how frequently I'll be able to do this (gas money, work, etc.) but I'm really looking forward to it. Thanks for the awesome adventure generator Randall! Also, thank you in advance to everyone else around my area who I may get the honor of meeting sometime. :D

User avatar
Clumpy
Posts: 1883
Joined: Thu Jul 19, 2007 4:48 am UTC
Contact:

Re: "Geohashing" discussion

Postby Clumpy » Sun May 25, 2008 7:15 am UTC

This one had me laughing so hard, I laughed myself right back around the scale to sad and fell into deep depression. Thanks a lot, XKCD!


Return to “Individual XKCD Comic Threads”

Who is online

Users browsing this forum: No registered users and 98 guests