xkcd

In today’s comic, I have the rain-stick thing happening in Jaynestown, when it actually happens in Our Mrs. Reynolds.  I lose three nerd points.

When writing the comic, I actually compiled a list of references to wood in Firefly by searching the scripts. They included Badger serving Jayne wood alcohol and Inara likening Mal’s sword technique to ‘chopping wood’ (both in Shindig). I should put it on Wikipedia so nobody has to duplicate my efforts.

Note: I actually wrote this post from the road early this morning to try to stave off the subsequent flood of email, but in my sleepiness I accidentally published it as a “page” instead of a “post” (a WordPress distinction that’s confused me before). So, all told, this was not a good day for my internet skills.  I think I’ve dropped from 1337 to 1334, maybe 1335 tops.

A while back, I was home in Virginia for a little while, and my friend James decided it was time to build a trebuchet

Pictured: James, Doug

I say measure once, cut eighty or ninety times.

As you can see by Doug’s hat, trebuchets are very serious business.

I had to leave before we could test it, but they finished up the last touches in my absence. This week, we got a chance to fire it for the first time.

The projectile (three full Dr Pepper cans taped together) vanished off into the woods. Firing successful! In the video, you can see falling leaves cut by the projectile.

In other news, Geohashing is working out wonderfully. At the most recent meetup I attended, we flew a camera from a kite and then tried to spell words under it.

There’s a new feature in the map-locating program where you can suggest and vote on alternate meetup sites for a given day. So far, the pattern is generally that we show up at the location, then find a nearby park or restaurant to hang out at. Bringing games and activities is encouraged.

I wasn’t able to make it to the most recent meetup because I was at MoCCA. By the way — thank you to Chris Hastings of Dr. McNinja for his generous hospitality. He gave me a place to sleep with no advance warning and didn’t even get mad when I spent the night sick on his couch, beat him at Mario Kart, and stole half his stuff. (If anyone wants a good deal on some of his erotic Batman fan art, let me know.)

This afternoon (starting 4:00-ish), some friends and I are heading to Belle Island in Richmond, VA, which is an alternate location for today’s geohash. I hear there are fireworks or something?

Geohashing has been great fun so far. There are hundreds of users on the wiki, and I’ve gotten to wander places like this:

There’s been a small change to the algorithm to deal with time zones. This change does not affect anyone in North/South America (excluding Greenland), does not affect Saturday meetup times anywhere, and does not change any currently known upcoming meeting times. The change:

For every location east of Longitude -30 (Europe, Africa, Asia, and Australia), use the Dow opening from the previous day — even if a new one becomes available partway through the day.

Put differently (the same functionally for everywhere except islands in the mid-Atlantic):

Consider any Dow openings published after noon local time to have occurred on the next day.

This is necessary to deal with time zone problems. For a lot of Europe, the Wednesday Dow opening was learned near sundown Wednesday, which meant they couldn’t use it to get to daytime meetups. For east Asia, they had to visit weekday locations the next day. A bunch of solutions were discussed, and I decided this was the cleanest.

The official map tool is being updated with the new behavior concurrently with this blog entry. The first coordinates that will be affected by it are Tuesday’s. Again, this does not affect anyone in the Americas.

Moving on — Saturday’s meetups are looking good! Today’s location in Boston was fantastic. I wasn’t planning to go, but it looked so interesting on Google Maps that we couldn’t resist checking it out. The picture above is one of several. Saturday’s meetup is in a less picturesque place than Friday or Sunday — suburban Hopewell. We’ll probably gather only briefly at the actual point, then head to the nearby state forest for walking or town center for food and such.

Also, good luck to phire, who was last seen on IRC an hour ago, leaving to mountain-climb to today’s coordinates in Christchurch, New Zealand. Congrats to the Denver graticules for getting organized so fast (and in a split city, at that!). And thanks to everyone for going along with this idea! The weekday trips have been great fun so far, and I look forward to getting the meetups going over the next few weekends!

Summer seems to have arrived, at last.

As you may have noticed, today’s comic contains an algorithm for converting dates into local coordinates. For a given day, you can calculate what that day’s coordinate is for your region. Dan has put together a tool for calculating a day’s coordinates and show it using Google Maps. Note that you can’t calculate a day’s coordinates before the stock market opens on that day (about 9:00 EST) — except for weekends and holidays, when it uses the most recent opening price.

We’ve been having fun trying to reach these coordinates for some time now, when the coordinate is reachable — that is, when it’s not over water, in a military base, or in the middle of Bill Gates’s house.

If you happen to be looking for somewhere to go, driving to the coordinates can be an adventure. If you do, please take pictures and drop them on the geohashing wiki (feel free to help fill it out).  I’m gonna get some rest and then, at 10 AM tomorrow, see if I can get to the Boston coordinates (I have no way of knowing where they’ll be until then, of course).

And finally, when the coordinates are reachable, meetups are Saturday afternoon at 4:00.

Edit: I answered a bunch of questions in a comment below.  Further discussion is also happening on the wiki. I’m going to get some sleep and then head out to today’s coordinates (or as close as I can get).

Last week, I wrote a short Python script that uses a USB GPS device under Linux to help with navigation.  It doesn’t have maps or anything — it just gives distances and, while you’re moving, the direction to the destination (as in “two o’clock”).  It prints this info on the terminal and speaks it using speech synthesis.

I joked about this in Comic #407, but it’s actually a pretty practical way to get around.  Just knowing what direction something’s in is a huge step toward finding it.  This past week I’ve used it successfully to find my way around towns I don’t know, and we even used it while driving to navigate to an out-of-town destination.

Plus, there’s the bonus that when you’re walking, wearing an earpiece, laptop in the bag, listening to the computerized voice whisper “TARGET DIRECTION THREE O’CLOCK DISTANCE ONE POINT THREE KILOMETERS ETA FIFTEEN MINUTES” into your ear, you feel like a cyborg.  I’ll have to set it up with a female voice and rename it “jane.py”.

Edit: I’ve just been testing the recent changes to this script, and it’s really not in a condition where I should be posting it anywhere.  But if you can use it as a starting point for hacking, here’s the link.  Some of you might find it useful sometime soon.

So there I was at the stroke of midnight, contemplating the four-knights opening by the dim glow of a flashlight, ears popping under the extra five pounds per square inch of pressure.

On Friday night, Dan (who you may remember as the Robot9000 bot author), Finn and I invented midnight underwater speed chess.

A nice feature is the naturally-enforced clock.  You have as much time per move as you have air in your lungs. Protip: don’t use a glass set.

Now we just need to combine it with chess boxing.

What’s the world’s center of population?

The center of population for a region is, roughly, the center of mass of the inhabitants. The Census bureau defines the center of population of the US (currently in Missouri) as

the point at which an imaginary, flat, weightless, and rigid map of the United States would balance perfectly if weights of identical value were placed on it so that each weight represented the location of one person on the date of the census.

This definition breaks down for populations on curved surfaces. For the earth as a whole, the center of mass obviously falls deep inside the planet.

This problem is easy to fix. I figure a better definition would be the point at which the sum of straight-line surface distances to each person is minimized. This is equivalent to the standard definition for a flat region, but it has the advantage that you can use it to define the center of population for a sphere.

I’ve never seen anyone who’s calculated the earth’s center of population so defined, but it doesn’t seem like it would be hard. Does anyone have the answer?

Bonus: find the center of population for other groups. What is the center of population of native English speakers? internet users? … bloggers?

Edit: I was standing the shower just now when I realized that the generalization I was using had to be wrong. I got it from this page on Wolfram Mathworld,

The centroid of point masses also gives the location at which a school should be built in order to minimize the distance travelled by children from cities, located at the positions of the masses, and with equal to the number of students from city (Steinhaus 1999, pp. 113-116).

and did try to check out the citation while writing, but it was to a book and I was much too lazy for that. However, I think the Wolfram paraphrasing is wrong — it’s not the distances that are minimized; it must be some other quantity. You can see that this is wrong for center-of-mass of two people at A and one person at B. It’s probably sums of squares that are minimized (as suggested in a comment, and which works for the three-person example) but I don’t see an obvious proof of this.

I was cleaning my room when I found this list in a pile of papers:

It’s my handwriting from the last couple years, and it looks faintly familiar, but for the life of me I have no idea what it means or why I wrote it.

… can anyone help figure this one out?

A number of people have asked me about building the robot sketched in yesterday’s strip. You’re definitely welcome to, and I’d love to see the results.

There are a couple engineering details that might trip you up. Rotating the webcam is one of them — I don’t make this explicit, but the idea in the blueprint was that there would be a servo inside the robot rotating the retaining magnets, which could be powered off the main battery. In practice, it might be better to put the servo on the outside and power it off the webcam battery — or, if you can find one cheap, simply use an omnidirectional camera.

The reason this is necessary is that I don’t think the internal robot, which is holding the webcam, will spin easily on hard surfaces. This is also the reason the robot uses Mechanum wheels instead of a simpler and cheaper design with a powered wheel on each side and castors or bearings on the front and back. If anyone has any ideas for making the robot spin more easily, I’d love to see them. Or perhaps you can try building the simpler design and see how quickly and reliably it can turn. If it works, it eliminates about half the cost of the project.

If anyone sends in any interesting material on this, I’ll be happy to put it up on a wiki somewhere so other people can tweak the design and develop a how-to. As far as I know, no one has built a robot quite like the one in the comic, so it’d be a great project.

Possible additional feature: cover the robot with little flaps or ridges, add some tweaks to protect the camera, and it becomes amphibious.

Edit: I’ve covered a few additional questions, including why the camera isn’t inside the ball, in this comment.

Quick, name a few recent popular movies where the two top-billed stars are female.

Here’s a miscellaneous survey I just did, tallied by gender of top billed/second billed star:

	M/M	M/F	F/M	F/F
20 biggest movies of 2007	10	10	0	0
20 biggest movies of 2006	11	7	0	2
20 biggest movies of 2005	11	7	2	0
20 biggest movies of 2004	10	9	1	0
20 biggest movies since 1977	15	5	0	0
IMDb Top 20 of All Time	15	5	0	0

There were about 110 movies with a male lead and 5 with a female lead. Of the second-billed females, nearly all are written as love interests of the first-billed man. There were over sixty movies in the sample with two male stars top-billed. The only movies with two top-billed female roles, on the other hand, were The Devil Wears Prada and Scary Movie 4.

My cousin has been working on tallying (by hand!) all movies with two top-billed female stars. She reports that there are staggeringly few of them, and the roles fall mainly in two genres: mother-daughter bonding movies and horror films.  Hollywood is not creating female heroes.

Suppose we had a generic Michael Bay/Jerry Bruckheimer movie with some evil organization (say, a shadow government headed by Dick Cheney or whatever) bent on destroying something (say, the internet). Who would you rather see battling their way through the system to stop them — another basic Bruce Willis/Denzel Washington/Vin Diesel character? Or River Tam, Sarah Connor, Lola from Run Lola Run, or Beatrix Kiddo? Not only could the film industry suck less in the examples it sets, we could have some awesome movies.

Notes: If anyone wants to expand my list into a more comprehensive and authoritative survey, I’d love to see the results. I did my tally by hand, using The Numbers for the basic lists and stars, plus IMDb and Wikipedia to get a consensus on billing order.