Skip to content

Instantly share code, notes, and snippets.

@natevw

natevw/gist:749615

Created December 21, 2010 07:27
Show Gist options
  • Star 0 You must be signed in to star a gist
  • Fork 0 You must be signed in to fork a gist
  • Save natevw/749615 to your computer and use it in GitHub Desktop.
Save natevw/749615 to your computer and use it in GitHub Desktop.
Download ZIP
feed-test
Raw
gistfile1.xml
<feed xmlns="http://www.w3.org/2005/Atom">
<title>a glob of nerdishness</title>
<id>http://www.extinguishedscholar.com/wpglob/?feed=atom</id>
<link href="" rel="self"/>
<generator>CouchApp on CouchDB</generator>
<updated>2010-11-27T16:52:00Z</updated>
<author>
<name>Nathan Vander Wilt</name>
</author>
<entry xml:base="http://rimsky-korsakov.local:5984/dev/_design/glob/_show/post/a_test_post">
<id>http://www.extinguishedscholar.com/wpglob/?p=815</id>
<title>Building CouchDB for PowerPC on Mac OS X 10.5 Leopard</title>
<content type="html">&lt;p&gt; My first Mac was a G4 mini which now mostly just serves an external drive to our home network as a Time Machine backup destination. Since it's powered up 24/7, I've been wanting to make a bit more use of it as a server, which means &lt;a href="http://couchdb.apache.org/"&gt;Couch&lt;/a&gt; of course. &lt;p&gt; Unfortunately, the process wasn't terribly "relaxing" — I couldn't find a PPC build of CouchDB for Mac OS X on the ENTIRE INTERNETS. Yet fortunately, after who knows how many hours of blood, sweat and swearing under my breath, I was able to coax out a working build. For the 3 other CouchDB fans out there who still have a PowerPC machine plugged in and enjoy sysadmin pain, here are my build notes: &lt;ol&gt; &lt;li&gt;First, install git if necessary and follow the instructions for the &lt;a href="https://github.com/couchone/build-couchdb"&gt;build-couchdb&lt;/a&gt; helper scripts until the "rake" part. &lt;li&gt;To avoid a mktmpdir issue in rake, you'll need to get a Ruby 1.8.7 version of Rake working. I don't recommend this route, but when it was all said and done I moved aside /usr/bin/ruby, /usr/bin/rake and /usr/bin/gem (each to /usr/bin/&lt;i&gt;X&lt;/i&gt;-orig) and then followed the first few steps of &lt;a href="http://hivelogic.com/articles/ruby-rails-leopard#ruby"&gt;these instructions&lt;/a&gt; to get newer versions working out of /usr/local/bin instead. &lt;li&gt;To avoid an unsupported architecture crash-and-burn, you'll need to go into build-couchdb/tasks/erlang.rake and comment out a 64-bit option line: &lt;code&gt;#configure.push '--enable-darwin-64bit' if DISTRO[0] == :osx&lt;/code&gt; &lt;li&gt;The CouchDB build doesn't like the Leopard version of libcurl, so build and install &lt;a href="http://curl.haxx.se/libcurl/"&gt;the latest from source&lt;/a&gt;. Temporarily move /usr/bin/curl-config to /usr/bin/curl-config-orig so the build process will use the right curl libraries. (Again, there's maybe a better way to do this, but I wasn't feeling picky at this point...) &lt;/ol&gt; &lt;p&gt; If any of that made any sense, and I didn't forget anything, you may even be able to reproduce this on your own PowerPC Mac at your own risk. PLEASE PLEASE PLEASE let me know if there's a better way to get build-couchdb using the right versions of Ruby and libcurl without desperately mucking around in /usr/bin like I did.</content>
<updated>2010-11-27T16:52:00Z</updated>
<link href="." rel="alternate"/>
</entry><entry xml:base="http://rimsky-korsakov.local:5984/dev/_design/glob/_show/post/another_test_post">
<id>http://www.extinguishedscholar.com/wpglob/?p=806</id>
<title>Fourth generation iPod touch camera focal lengths</title>
<content type="html">&lt;p&gt; Late one night soon after I bought my fourth generation iPod touch, I did some sloppy measurements to try figure out the 35mm equivalent focal length of each of its two cameras. Here is a sloppy summary of my findings. &lt;p&gt; &lt;img src="http://www.extinguishedscholar.com/wpglob/wp-content/uploads/IMG_0101-300x225.jpg" alt="View from the iPod" title="View from the iPod"&gt; &lt;p&gt; The display on my MacBook is 11 5/16 inches wide (287.3375 mm). It fills the back ("720p") camera width at a distance of 14 3/16 inches (360.3625 mm). It fills the front ("FaceTime") camera width at distance of 11 inches (279.4 mm). &lt;figure&gt; &lt;img src="http://www.extinguishedscholar.com/wpglob/wp-content/uploads/iPod-focal-length-setup.png" alt="iPod focal length setup" title="iPod focal length setup"&gt; &lt;/figure&gt; &lt;p&gt; Using some &lt;a href="http://en.wikipedia.org/wiki/Angle_of_view"&gt;basic trigonometry&lt;/a&gt;:&lt;br&gt; &lt;code&gt; a = 2 arctan (d/2f) # a = angle, d = dimension (my "width"), f = focal length, or, subject distance &lt;/code&gt;&lt;br&gt; ...we can find each camera lens's angle of view:&lt;br&gt; &lt;code&gt; 2*Math.atan2(287.3375, 2*360.3625) = 0.7587331199535923 radians (43.47 degrees)&lt;br&gt; 2*Math.atan2(287.3375, 2* 279.4) = 0.9498931263447237 radians (54.42 degrees) &lt;/code&gt; &lt;p&gt; Standard &lt;a href="http://en.wikipedia.org/wiki/135_film"&gt;135 film&lt;/a&gt; is 35mm wide, and it is on this format I wanted to figure out the iPod lens equivalent. I massaged the angle of view calculation into a form that could yield a focal length based on an angle:&lt;br&gt; &lt;code&gt; tan(a/2) = d/2/f &lt;/code&gt;&lt;br&gt; For 35mm equivalent, I plugged in 35 for d ("dimension", my "width") and solved for focal length as a function of angle:&lt;br&gt; &lt;code&gt; tan(a/2) = 17.5/f&lt;br&gt; f = 17.5/tan(a/2) &lt;/code&gt; &lt;p&gt; So, the front ("720p") camera has a focal length equivalent to a 44.9mm lens on a 35mm film camera body (or a 27.44mm lens on an APS-C body). The back "FaceTime" camera is wider, equivalent to a 34.0mm lens on a 35mm film body (or a 21.25mm lens on an APS-C body) &lt;p&gt; Then I looked at the EXIF metadata to see what it says about the camera. For the 720p camera, the metadata records a focal length of 3.9mm. If my 35mm equivalent focal length calculations are correct, this means a &lt;a href="http://en.wikipedia.org/wiki/Crop_factor"&gt;crop factor&lt;/a&gt; of 11.26 and thus a 3.11mm sensor width. &lt;p&gt; Now for the FaceTime camera, the EXIF metadata records a focal length of 3.9mm. Again? So allegedly this would be a 8.72 crop factor and 4.02mm sensor size. However, this camera is lower resolution (640×480 versus 960×720) and I have a hard time believing that it is a larger sensor. (If it were, the per-pixel area would be significantly larger and I'd expect much better quality and low light performance than the back camera.) I suspect the focal length metadata is (or at least was when I first looked...I should check again on the latest iOS) simply wrong for pictures taken with the FaceTime camera.</content>
<updated>2010-11-16T17:16:00Z</updated>
<link href="." rel="alternate"/>
</entry></feed>
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment