Shallow Thoughts : : Nov

Akkana's Musings on Open Source Computing and Technology, Science, and Nature.

Wed, 24 Nov 2010

Article: Troubleshooting running processes, part I

How do you troubleshoot a process that's running away, sucking up too much CPU, or not doing anything at all? Today on Linux Planet: Troubleshooting Linux Servers: top and Other Basic System Tools.

This is part I, covering basics like top, strace and gdb. Part II will get into hairier stuff and tips for debugging Python applications.

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[ 21:06 Nov 24, 2010    More linux | permalink to this entry | comments ]

Sun, 21 Nov 2010

Lunar Water Strip-Mines?

You may have seen the headlines a few weeks ago, when everyone was crowing "Water on the Moon!" after the LCROSS results were finally published. Turns out the moon is wetter than the Sahara (woo!) and all the news sites seemed excited about how we'd be using this for a lunar base. It only takes a ton of rock to get 11-12 gallons of water!

I wondered, am I the only one who thinks 12 gallons isn't very much? I couldn't help envisioning a tiny lunar base surrounded by acres of mine tailing devastation.

So I calculated how much rock it takes to make a ton (assuming basalt; lunar highland anorthosite would be a little less dense). Turns out it's not very much: a ton of basalt would make a cube about 8.6 feet on a side. So okay, I guess it would take quite a while to work up to those acres of devastation. It was an interesting calculation, anyway; rock is a lot less dense than I thought.

You can read the details in my SJAA Ephemeris column this month, Full of Moon.

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[ 19:55 Nov 21, 2010    More science/astro | permalink to this entry | comments ]

Mon, 15 Nov 2010

More advanced GIMP tricks for cutting parts out of photos

[Butterfly in space, screenshot]

My previous Linux Planet article covered beginner tips for cutting foreground objects out of photographs. Part 2, from last week, covers some more flexible advanced techniques you'll want to use as your GIMP skills increase.

Find out how to put a butterfly in space!

Read it here: More GIMP tricks for cutting objects of photos

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[ 15:14 Nov 15, 2010    More gimp | permalink to this entry | comments ]

Mon, 08 Nov 2010

No (live) tarantulas, but lots of woodpeckers

November is normally far too late for tarantulas to be on the move -- mid-October is their normal season around here. But a friend commented she'd seen some at Alum Rock last week, so over the weekend we hauled ourselves out there and went hunting.

And we saw tarantula sign -- unfortunately consisting of two dead tarantulas lying mangled on the trail. No live ones. It was an unseasonably warm day, so perhaps it was too hot and the spiders were still hiding in their holes.

[Acorn woodpecker] It was lovely walk nevertheless. We saw a six-point buck chasing a doe with two other does trailing behind him ... why were the does following? No idea, but the whole procession crashed around through the brush and eventually came out and crossed the trail right behind us. We gave them space -- you don't want to get too close to a buck during this season.

And the pecking was fierce over by the dead Eucalyptus above the end-of-the-road parking lot, where a large family of acorn woodpeckers were pecking and laughing chattering as they stored their acorns for the winter. We saw at least seven on the tree at once, though counting was tricky because birds kept flying off to find more acorns while other birds flew in.

Most of the ground squirrels have already retired for the cold season -- we only saw a few out, fattening up before hibernation -- but we heard quite a few invisible chipmunks giving their sonar-ping calls as we walked past.

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[ 23:02 Nov 08, 2010    More nature | permalink to this entry | comments ]

Wed, 03 Nov 2010

Garmin GPX timestamp bizarreness

My last entry mentioned some work I'd done to one of my mapping programs, Ellie, to gather statistics from the track logs I get from my Garmin GPS.

In the course of working on Ellie, I discovered something phenomenally silly about the GPX files from my Garmin Vista CX, as uploaded with gpsbabel.

Track log points, quite reasonably, have time stamps in "Zulu time" (essentially the same as GMT, give or take some fraction of a second). They look like this:

<trkpt lat="35.289519913" lon="-115.227057561">
  <ele>1441.634277</ele>
  <time>2010-10-14T17:51:35Z</time>
</trkpt>

But the waypoints you set for specific points of interest, even if they're in the same GPX file, have timestamps that have no time zone at all. They look like this:

<wpt lat="35.334813371" lon="-115.178730609">
  <ele>1489.917480</ele>
  <name>001</name>
  <cmt>14-OCT-10 11:18:51AM</cmt>
  <desc>14-OCT-10 11:18:51AM</desc>
  <sym>Flag, Blue</sym>
</wpt>

Notice the waypoint's time isn't actually in a time field -- it's duplicated in two fields, cmt (comment) and desc (description). So it's not really intended to be a time stamp -- but it sure would be handy if you could use it as one.

You might be able to correlate waypoints with track points by comparing coordinates ... unless you spent more than an hour hanging around a particular location, or came back several hours later (perhaps starting and ending your hike at the same place). In that case ... you'd better know what the local time zone was, including daylight savings time.

What a silly omission, considering that the GPS obviously already knows the Zulu time and could just as easily use that!

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[ 22:09 Nov 03, 2010    More mapping | permalink to this entry | comments ]