Wednesday, 31 August 2011

Reverse engineering SARS' queueing system

On Monday I had to visit SARS to submit an IRP6.  I'm what's called a "provisional taxpayer", which means I get to deal with the taxman about twice as often as people who aren't.

Previously their queueing system was just a long line of people waiting their turn.  Then, some years ago they started offering chairs - a little more comfortable, but the queueing system was basically the same: one's seat determined one's position in the queue, so it was like a big game of Musical Chairs.  And finally, about a year ago, SARS started issuing numbers at the reception desk: one could now sit anywhere and simply wait right there until one's number came up.  The numbers appear on a screen, but also, a Stephanie Hawking type computer voice reads the numbers aloud.

I had been trying to read a few pages of The Great Disruption, but Stephanie's staccato voice proved too distracting - like a numbers station's siren call.  So I decided to make lemonade.  For a bit more than an hour I jotted down the time and the new number - with the aim to write exactly this post.

Now that I see the graph, it's a bit disappointing.  I was hoping to see points along more lines of different slopes and intercepts than the two segments visible here - which I know both to be from the "INCOME TAX RETURNS" stream.  (By the way, why are these things always in all-caps?)  There seemed to be multiple virtual queues running simultaneously, each allocating numbers from distinct ranges.  Perhaps I just didn't collect enough data - perhaps somebody needs to spend a whole day there.  Maybe next time.

Wednesday, 24 August 2011

Time lapse movie from stills recipe

Using external tools to sort stills, and stdin as "listfile":

ls -rt webcam-20110819-1* |mencoder -o /tmp/couch.avi -mf fps=10:type=jpg mf://@/dev/stdin -ovc copy

I need this to check if the dog lies on the couch while I'm out shopping!

Monday, 22 August 2011

How many people get hit by celebratory gunshots into the air?

Nissemus tweets:
Wonder how many people have been hit by "celebratory" rounds fired into the air falling back to earth? #Libya
I've often wondered the same.  I think the number must be quite low.  Factors to consider:

  • If fired at a steep angle, the bullet is in the air so long that it has time to bleed off excess velocity, and to reach terminal velocity on the way down.  While still dangerous, possibly lethal (depending what part of the body it hits), it is not as dangerous as a bullet fired straight at a living target.
  • It will be very difficult to fire a round such that the projectile lands anywhere near the point of firing. If a large number of people celebrating a victory are gathered together, then a celebratory round fired from that crowd will be unlikely to hit anyone in that crowd.
  • Outside of such a gathered crowd, the density of people outdoors will be comparatively low.  Manila has the highest population density at 43079/km²; if every last resident of Manila proper were outdoors, they would still only cover about 1/50th of the target surface area available to an unaimed bullet.
  • Tripoli, specifically, is not as densely populated as Manila; Wikipedia notes a density of 4205/km².
  • Let's allow that most Tripoli residents are outdoors during the celebrations.
  • An upright human body might present about 0.5m² cross section for a falling bullet to hit.  Sometimes more, sometimes less.  Let's err on the side of caution.
Then, of every km² of land area, humans in Tripoli occupy at most about 2000m².  That is, 0.2%.  My guesstimate of an answer then to Nissemus' question would be that you might see one falling-bullet injury (not all of which would result in death) for every 500 rounds fired.