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NWCLARK TPF grant report #51

From:
Nicholas Clark
Date:
September 7, 2012 13:23
Subject:
NWCLARK TPF grant report #51
Message ID:
20120907202258.GD9834@plum.flirble.org
I didn't do anything billable this week, as I was at YAPC::Europe, and then
felt completely shattered afterwards and took the next few days off.

I did ask Larry what the story was behind pack and Venus, and wrote it down
before I forgot it:

Larry recalls that the hex and bit string formats (H, h, B, b) were added to
pack for processing data from NASA's Magellan probe. Magellan was in an
elliptical orbit, using the antenna for the radar mapping when close to
Venus and for communicating data back to Earth for the rest of the orbit.
There were two transmission units, but one of these failed, and then the
other developed a fault whereby it would randomly flip the sense of all the
bits. It was easy to automatically detect complete records with the correct
sense, and complete records with all the bits flipped. However, this didn't
recover the records where the sense flipped midway. A colleague of Larry's
was able to pretty much eyeball where the records flipped, so they wrote an
editor named kybble (a pun on the dog food Kibbles 'n Bits) to enable him to
manually correct the records and recover the data. For this purpose pack
gained the hex and bit string format specifiers.

Nicholas Clark



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