Category Archives: linux

ffmpeg on raspbian / Raspberry Pi

Since http://www.jeffreythompson.org/blog/2014/11/13/installing-ffmpeg-for-raspberry-pi/ is a bit messy, here is how you can compile ffmpeg with x264 on raspbian. Changes are building in your home directory, getting just a shallow git clone and building with all CPU cores. Also no unnecessary sudo…

Read the comments below!

# In a directory of your choosing (I used ~/ffmpeg):

# build and install x264
git clone --depth 1 git://git.videolan.org/x264
cd x264
./configure --host=arm-unknown-linux-gnueabi --enable-static --disable-opencl
make -j 4
sudo make install
 
# build and make ffmpeg
git clone --depth=1 git://source.ffmpeg.org/ffmpeg.git
cd ffmpeg
./configure --arch=armel --target-os=linux --enable-gpl --enable-libx264 --enable-nonfree
make -j4
sudo make install

Read the comments below!

Hopefully someone, somewhere will provide a repository for this kind of stuff some day.

It takes just 25 minutes on a Raspberry Pi 3. Not hours or days like some old internet sources on old Raspis say.

In case you are wondering v4l2 should work with this.

Let’s Encrypt with Lighttpd

Save the page https://gethttpsforfree.com/ locally and use a clean browser to open the HTML file.
Create your keys and everything.
Cat domain.key and chained.pem into a new pemfile.
Grab the Let’s Encrypt Authority X1 (IdenTrust cross-signed) pemfile from https://letsencrypt.org/certificates/
Put those two files in a safe place on your server.
Don’t forget to set proper permissions on the files.
ssl.ca-file = "/path/to/lets-encrypt-x1-cross-signed.pem" # the Let's Encrypt certificate
ssl.pemfile = "/path/to/pemfile.pem" # your pemfile

Restart lighttpd.
Done.

Converting coordinates with cs2cs

In the spirit of Blog Little Things and after reading WEBKID’s You Might Not Need QGIS earlier, here you go:

So you have thousands or millions of coordinates in “the wrong” or “that stupid” coordinate reference system and want to convert them to “the one you need”? Easily done with proj‘s cs2cs tool. You feed it a list of coordinates and tell it how you want them transformed and put out.

Let’s say you have these crazy accurate super coordinates in EPSG:4326 (WGS84) in a file called MyStupidCoordinates.txt (for example from copying columns out of Excel).


9.92510775592794303 53.63833616755876932
9.89715616602172332 53.61639299685715798
9.91541274879985579 53.63589289755918799
9.91922922611725966 53.63415202989637010
9.92072211107566382 53.63179675033637750
9.89998015840083490 53.62284810375095390
9.90427723676020832 53.60740624866674153
9.95012889485460583 53.64563499608360075
9.89590860878436196 53.62979225409544171
9.92944379841924452 53.60061248161031955

and you want them in the much superior and wonderfully metric EPSG:25832 (ETRS89 / UTM zone 32N). You simply use +init=sourceCRS +to +init=targetCRS. if you have no idea what CRS your coordinates are in, enjoy 5 minutes with http://projfinder.com/ and you will either know or you might want to take a walk (don’t forget to try them flipped though).

cs2cs +init=epsg:4326 +to +init=epsg:25832 MyStupidCoordinates.txt

and it will print


561164.00 5943681.64 0.00
559346.79 5941216.81 0.00
560526.52 5943401.54 0.00
560781.36 5943211.12 0.00
560883.46 5942950.37 0.00
559524.51 5941937.29 0.00
559830.54 5940223.00 0.00
562807.40 5944515.43 0.00
559245.50 5942706.43 0.00
561505.49 5939488.65 0.00

You probably want more decimal places though, since your input coordinates were accurate down to the attodegree. For this, you can specify the output format with -f

cs2cs +init=epsg:4326 +to +init=epsg:25832 -f "%.17f" MyStupidCoordinates.txt


561164.00100000295788050 5943681.64279999211430550 0.00000000000000000
559346.79200000269338489 5941216.80899999570101500 0.00000000000000000
560526.52400000276975334 5943401.53899999428540468 0.00000000000000000
560781.36300000245682895 5943211.12199999392032623 0.00000000000000000
560883.46400000224821270 5942950.37499999348074198 0.00000000000000000
559524.51200000231619924 5941937.29399999510496855 0.00000000000000000
559830.54200000269338489 5940223.00299999490380287 0.00000000000000000
562807.39800000295508653 5944515.43399999290704727 0.00000000000000000
559245.50000000221189111 5942706.42899999395012856 0.00000000000000000
561505.48800000257324427 5939488.65499999187886715 0.00000000000000000

Perfect!

You could direct these transformed coordinates into a new file called MyCoolCoordinates.txt by adding a redirection of its output:

cs2cs +init=epsg:4326 +to +init=epsg:25832 MyStupidCoordinates.txt > MyCoolCoordinates.txt

You can find out more about cs2cs by reading its manpage:

man cs2cs

PS: You can handle that Z coordinate, right?

Partial 3D model of Comet 67P/Churyumov-Gerasimenko through photogrammetry

The ESA asked people to use their imagery of the Comet 67P/Churyumov-Gerasimenko. They released an archive of photos under the CC BY-SA. I took them, threw them into a trial version of Agisoft Photoscan and generated a textured mesh in it. I then exported it as .obj-model, loaded it in Blender and exported it to a WebGL scene with blend4web. In other words, I just threw some programs at it.

67p_photoscan_blend2web

You can see the result in your browser at http://hannes.enjoys.it/geo/67p.html (~7 Megabytes). Be aware that while I used a lower quality version for this web version, the higher quality versions I tried were not actually that much “better”. The quality is limited by the resolution of the imagery and of course the fact that we do not have full coverage of a well-lit comet. Still totally fascinating and lots of fun to try.

You can download a higher quality .obj at http://hannes.enjoys.it/geo/67p.7z (~12 Megabytes), you can import that straight into Blender.

Now could someone turn the VisualSFM suite into something that is fun to use on Linux so I can try without Photoscan? ;)

PS: I should add that I have not used Photoscan without ground control points for a completely foreign object before. Someone with more experience should be able to get a better result out of it. If you do and you read this, please share your wisdom!

“Commandline File Hosts”

These are the “terminal to URL” file hosts I know. Please tell me about others. The speed tests are not scientific at all, my servers might be uncapable of better speeds because of saturation or bad routing.

https://transfer.sh/

curl --upload-file "01_Name_Game_(Intro).mp3" https://transfer.sh/

Maximum Filesize: 5 Gigabytes
Expiration after: 2 weeks
Uses HTTPS!
Serves error 500 for non-existing files. Does not serve direct downloads anymore. Bleh.
Download URLs are modeled after your original filename (“special” characters are replaced): https://transfer.sh/SGNl/01-name-game-intro.mp3
1GB.zip upload: ~30-110 Megabit/s
1GB.zip download: ~240 Megabit/s

http://curl.io/

curl -F "file=@01_Name_Game_(Intro).mp3" http://curl.io/send/abcd1234

Maximum Filesize: 20 Gigabytes
Expiration after: 4 hours
Requires you to visit their website to get a key (URL) assigned.
Download URLs are random and but it serves original filename with content-disposition: http://curl.io/get/kegcxfza/85866a9bcfaf6f8eccab136238c07f659d580b25
1GB.zip upload: ~60-75 Megabit/s
1GB.zip download: 100 Megabit/s

http://chunk.io

curl --upload-file 01_Name_Game_\(Intro\).mp3 chunk.io

Maximum Filesize: 50 Megabytes
Expiration after: 6 months
They might increase filesize and expiration if there is enough interest, as of now you can not “sign-up” for those.
Download URLs are unreadable, filenames are lost: http://chunk.io/f/afb01d527ceb4d03b9bf9e62bb32263e
1GB.zip upload: ~8 Megabit/s (until it errored :) )

http://purrrl.link/
Requires sign-up.

Shutting down the operating system by playing a “kill song” in MPD

I use a 20€ Dockstar with Archlinux ARM on it as MPD music server. Since I like to turn off electronic devices when they are not needed and pulling the plug is not something you should do to running computers, I was looking for a solution to somehow shut it down from any mpd client. So I added a specific song as “shutdown file”. Once that song is played, the system will cleanly shut down and power off.

Here is the systemd .service file I came up with:

# cat /etc/systemd/system/mpdtosystemshutdown.service
[Unit]
Description=MPD to system shutdown

[Service]
ExecStart=/bin/sh -c "sleep 10 && /usr/bin/inotifywait -e open /path/to/path/music/shutdown.mp3 && mpc clear && shutdown -h now"

[Install]
WantedBy=multi-user.target

You need: inotify-tools and mpc (in addition to mpd)

  1. The service sleeps for 10 seconds in the beginning because I keep the music on an external USB harddisk which gets mounted after the multi-user target is reached. This is an ugly workaround but should be good enough. A better solution would be using a udev rule or systemd mount unit to only start the service when the harddisk is mounted.
  2. Then inotifywait will monitor shutdown.mp3 for being opened by mpd (or anything else). Once this happens inotifywait will quit successfully.
  3. mpc will clear the mpd playlist as you do not want shutdown.mp3 to be played again right after booting, do you? I surely did not.
  4. Finally the system is being shut down and powered off.

You probably have to add shutdown.mp3 to your mpd database before starting this service or the database update might trigger it. Updating the database afterwards is save and does not trigger the shutdown.

Don’t blame me if this ends up with an infinite reboot loop.