US Air Traffic

Found this fascinating video of US air traffic over a day. I can’t imagine how much fuel that lot burnt up over the course of the animation.

Found via LawGeek.

Meloe Proscarabaeus

Found this unusual beetle:

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A little research revealed that it is an oil beetle, genus Meloe. I’m not too sure on the species, but the Proscarabaeus is most common in the UK and blue-black, so I’ll plump for that one. Though, according to my invaluable book, it’s a big one.

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More Conjoined Grapes

A quick search on Google revealed that my conjoined grapes are by no means unique.

There’s two more examples here along with some other foodal anomalies.

Space Research and Pretty Pictures

I know there’s more to space research than pretty pictures, but there do seem to be a lot of them about at the minute. ESA’s Mars Express has snapped this little lot of the northern pole’s ice cap (and a other interesting features.)

Then there’s Cassini, which is still out there, producing some stunning pictures. There’s the Hubble telescope too, which looks like it might last a bit longer still, after a little jiggery-pokery.

Precision and Accuracy

I was pleasantly surprised at the accuracy of the tracks I was getting out of my GPS unit until the other day.

Then I noticed something odd; the tracks in places follow a very smooth curve, apparently matching the road I was following. At certain points there are glitches, where the track jumps a few metres then carries on in a smooth curve.

The Above image shows the same section of path walked on two separate occasions. Note how the track for the higher resolution data (yellow) deviates from the former track. Also note the sudden re-alignment and the consequent parallel nature of the paths. (Scale of 1m/pixel)

This highlights to me, the difference between precision and accuracy. The precision of GPS units looks impressive, but precision is not the same as accuracy.

Precision is how well defined a value is, for example 3.141593, is precisely defined to the 6th decimal point. This does not mean, however that the value is correct - i.e. it is not necessarily accurate.

Accuracy is a measure of how correct a value is, for example 3.14 ± 0.02. This tells us that there’s no point in quoting a precision of six decimal places (as above) because the remaining four decimal places will almost certainly be wrong.

Relating this back to my GPS example we can see that the unit precisely tracked a curve, but not necessarily the correct curve. The curve looks correct because it precisely follows a neat curve, but it is not accurate because it is the wrong curve.

I’m assuming that the jump occurs when the unit locks to a new satellite, or a building reflects the signal.

Zissou

Go and see Life Aquatic. It’s brilliant and I’m not the only one who thinks so.