Archive for January 2007

Riding the BART back to SFO

26 January 2007
Categories: Transportation

I like the BART, even if the grungy upholstered seats do creep me out a little. There are several details to aid passengers that show that some good thought was put into it…

  • Computer-generated voices tell not only what kind of train is boarding, but also how long the wait will be until the next several trains arrive.
  • The voice is female for platform 1 (southbound) and male for platform 2 (northbound)—so once you’ve heard one announcement, for every one thereafter you instantly know as the announcement begins whether the info will be pertinent for your direction of travel.
  • Tactile warning strip along the edge of the platform, for the benefit of the visually impaired, changes colour and pattern (parallel bumps rather than diagonal, like the difference between the stars on 48- and 50-star flags) at the places where the doors of the train will be—and some of these have additional washboard strips further in from the edge, but only in the places where a 2-car train, the minimal length, will stop. That way those 4 door locations are always guaranteed to have a door.

Oddly, there are a number of things here that you don’t see on the CTA:

  • Prominent signs for fire extinguishers
  • Posted explanations for how to manually override the doors
  • A station sign showing the location of the emergency third rail cut-off

I’m sure all these things exist on the CTA (well, not sure about the extinguishers, but the door overrides and power cut-offs definitely do), but attention is not called to them—it would only serve as an invitation to tamper with them. Don’t know how many times I’ve seen some jerk pull the (unmarked) red ball to get off just a few seconds sooner than everyone else, or to make up for (nearly) missing their stop. Yet in San Francisco, knowledge of these items is boldly promulgated, and the public is trusted to use that information appropriately. Go figure.

Later, aboard the plane, I got to wondering… Why should the overwing doors not be used in the event of a water landing? And, if the bag dangling from the oxygen mask does not inflate, what’s it there for?

Arrrrgh… Mythbusters misses the boat

21 January 2007

Mythbusters put on a very fun two-hour “Pirate Special” recently. It addressed a Hollywood staple of swashbuckling—leaping from a yardarm and using a dagger stabbed through the face of a sail to slow one’s descent to the deck (“busted”)—as well as the fascinating revisionism that pirates wore eyepatches not due to opthalmological damage, but rather to give one eye the benefit of night vision when charging below decks during daylight attacks (intriguingly “plausible”).

Unfortunately, they came to the wrong conclusion for the prime “myth” addressed on this episode, which was this: in battle, a pirate is more likely to take damage from the splinters a cannonball produces in striking the ship, rather than from the cannonball itself.

The Mythbusters verdict? “Busted.”

The reason? They were unable to produce the requisite money shot on camera, that of a viciously long and sharp splinter of oak stabbing gruesomely through the flesh of a dead pig carcass.

Despite the explosive violence of impact the pigs appeared unharmed, and Jamie and Adam claimed that, despite the scary-looking clouds of debris flying around, it just wasn’t as dangerous as a fast-moving iron ball, which they showed could penetrate four back-to-back pigs with velocity to spare. Sure, a direct hit from a cannonball is going to be devastating. But to call the wood shrapnel “harmless” flies completely in the face of the historical record, which shows that death and injury from large splinters of wood was commonplace in the era of wood-hulled naval warfare. (Adam, seeking consolation, lamely suggests that perhaps a scratch from the splinters could cause a nasty infection, given the microbes living on the wood and the poor hygiene of the day.)

Their conclusion also ignores the evidence of their own high-speed footage, which shows what looks to be a five-foot length of two-by-six lumber being knocked completely free of their solidly built ship’s hull mock-up and striking two of the pigs in the head with enough force to cause the board to flex. Sure, it’s not a jugular-gouging shard, but that’s bound to hurt.

The reason they misjudged the potential of shrapnel damage can be summed up in Jamie’s last line: “Maybe we should try a bigger cannon.” Their final test used a mid-1880s-era replica firing 6-pound shot. According to Patrick O’Brian’s Men-Of-War: Life in Nelson’s Navy, this is on the very small end of the cannonball scale: 12-, 18-, 24-, and 32-pounders were commonplace, “and a 32-pounder could smash through two feet of solid oak at half a mile.” You can’t tell me that’s not going to generate big, sharp splinters moving at deadly velocity.

What they ultimately ignored was the wording of the myth in the first place. Setting aside their mishandling of the “amount of damage” assessment, the operative question is the likelihood of being hit by one or the other. This becomes a question of statistics, and area of effect—one which was answered in their very first sub-scale test.

Using an air cannon and a 2-inch ball bearing, they fired shots at boards of pine, white oak, and red oak. Behind the boards were two backstops coated with foam board to catch splinters, each placed at a 45° angle to the target board and with enough gap between to allow the shot to pass through to a sandbag backstop behind.

In these tests, the answer was clear: the cannonball will do damage to anything it strikes, which in this case was a field of damage along an imaginary cylinder only two inches in diameter. Meanwhile, shrapnel blasted away from the point of impact in a broad cone—making the field of potential damage several feet wide within just a few feet. Unless your pirates are ludicrously lined up in close proximity (as the pig carcasses were in one of the scale tests), and hit by a very lucky dead-on shot (a one-in-a-million shot when using inaccurate iron cannons on the high seas), the odds are much, much greater that they will be hit by wood shrapnel instead of cannonballs.

I hope the Mythbusters find that bigger cannon, and a place to fire it, so they can revisit this “myth” and demonstrate, conclusively, that it is most definitely “confirmed.”

Minor tweak, major improvement

3 January 2007
Categories: Self-referential

On Tuesday, 2 January 2007, I made a minor update to my Blues Brothers map that both improved its function and reduced the number of extraneous image GETs.

The long of it… Previously, when clicking on a marker, the popup balloon would be undersized for the content. Part of the screen capture image and any text below it would be superimposed on the map rather than on a nice clean white background, making it hard to read. Clicking on the marker a second time would redraw the balloon in a proper size, but each click sends another GET command for the image (even though the subsequent clicks usually result in a “304 – not modified” response).

I was stuck on thinking that a fix would require some complicated and obscure tweaking of the Google Maps API, but the actual solution is mindlessly simple. My sudden realisation may be considered a dope-slap epiphany. When the balloon is first drawn, the image has not yet been downloaded, so the browser doesn’t know how big it is. It assumes that the image is 0 pixels high, and draws the balloon accordingly. (This seems like a silly assumption, but I suppose it’s better than assuming it’s 1000 pixels high.) Then the image is downloaded, and since it’s much more than 0 pixels high, it overshoots the bottom of the balloon. Follow-up clicks redraw the balloon, and now since the browser knows the image size in advance, the balloon is drawn in a proper size.

To fix it, all I needed to do was include the height of the image in its tag, thus giving the browser advance warning. I added another variable to the data set: iheight. The elegant part of this is that with only a few exceptions, all of the images are 100 pixels high. Therefore the iheight declaration only needs to be included in the exceptional entries. The code now checks for iheight==null, and if so automatically sets the value to 100. All the code to accomplish this only increased the total download size by 207 bytes. This margin is more than absorbed by a reduced need to click twice on each marker.

By early Wednesday morning, the logs were showing success. A visitor arrived and viewed nearly every marker on the map—yet only clicked once on each.