By far the easiest method of configuring a fleet of Compound Pi servers is to get a single Pi running the Compound Pi daemon successfully, using an automatic network configuration, then clone its SD card for all the other Pis.
This quick start tutorial assumes you are using the Raspbian operating system on your Pis, and Ubuntu as your client.
Before doing anything it’s worth thinking about what hardware to use in your setup. Firstly, there’s the selection of Pi to use. The primary concern here is RAM size. Compound Pi uses each Pi’s memory to store captured images to avoid dealing with any lengthy delays writing to SD cards (this isn’t simply a matter of slow SD cards, but avoiding periodic flushes of the Linux disk cache which can severely impact the timing of shots).
To this end, the more RAM in your Pi, the better. Compound Pi is capable of running on a model A or A+ (256Mb of RAM) but after the GPU has taken its share (128Mb) and the OS and Compound Pi server have grabbed theirs, there’s typically less than 100Mb left for data storage. The model B or B+ (512Mb of RAM) is a better selection typically providing over 300Mb of temporary data storage. However, the Pi 2 model B (1Gb of RAM) is the obviously the ultimate choice as it typically has 800Mb or more of available memory for data storage, and the faster processor doesn’t hurt either.
The next important selection is the network between your client and Pi servers. Compound Pi can run over WiFi (in fact, this was the first configuration it was tested in) but there are numerous reasons why WiFi is sub-optimal:
While WiFi may be tempting because of the lack of wires needed between the client and all the Pi servers, it is certainly not the optimal setup for running Compound Pi.
Although it costs significantly more, the ultimate Compound Pi setup would involve power over Ethernet (POE), allowing a single cable to run to each Pi carrying both data and power. Given you have to run one cable anyway for power, this minimizes the number of cables, while providing the best connectivity. The only downside is the cost of a POE capable switch (typically >$100) and a POE HAT for each Pi to split out the power from the data.
Ensure your Ubuntu client machine is connected to the same network as your Pis (whether by Ethernet or Wifi doesn’t matter). Then, execute the following to install the client and an NTP daemon:
$ sudo add-apt-repository ppa:waveform/ppa
$ sudo apt-get update
$ sudo apt-get install compoundpi-client ntp
The NTP daemon will most likely be installed to synchronize with an NTP pool on the Internet (e.g. pool.ntp.org). This is fine, but check that it’s working with the following command line:
$ ntpq -p
remote refid st t when poll reach delay offset jitter
==============================================================================
*aaaaaaa.aaaaaaa nn.nnn.nnn.nnn 3 u 109 1024 377 4.639 -2.101 21.233
On the Pi you intend to clone, configure networking to use DHCP to automatically obtain an IP address. Edit the /etc/network/interfaces file and ensure that it looks similar to the following:
auto lo
iface lo inet loopback
iface eth0 inet dhcp
allow-hotplug wlan0
iface wlan0 inet manual
wpa-roam /etc/wpa_supplicant/wpa_supplicant.conf
iface default inet dhcp
This configuration should ensure that the first Ethernet and/or WiFi interfaces will pick up an address automatically from the local DHCP server. If you are using WiFi, complete the WiFi configuration by editing the /etc/wpa_supplicant/wpa_supplicant.conf file to look something like the following:
ctrl_interface=DIR=/var/run/wpa_supplicant GROUP=netdev
update_config=1
network={
ssid="my_wireless_ssid"
psk="my_wireless_password"
proto=RSN
key_mgmt=WPA-PSK
pairwise=CCMP
auth_alg=OPEN
}
Execute the following command to install the Compound Pi server package and the NTP daemon (the latter is required for time-synchronized image capture):
$ sudo apt-get install compoundpi-server ntp
This should pull in all necessary dependencies, and automatically install an init-script which will start the Compound Pi daemon on boot-up. Test this by rebooting the Pi with a camera module attached. You should see the camera module’s LED light up when the daemon starts. If it doesn’t, the most likely culprit is the camera: try running raspistill, ensure you’ve activated the camera with sudo raspi-config, and ensure the CSI cable is inserted correctly. You can control the Compound Pi daemon as you would any other system daemon:
$ sudo service cpid stop
$ sudo service cpid start
$ sudo service cpid restart
Ideally, you want all your Pi servers to sync with the NTP time server you set up on your client. Edit the /etc/ntp.conf file and replace the server lines with the IP address of your client (ideally you should configure your router to give your client a fixed address):
...
#server 0.debian.pool.ntp.org iburst
#server 1.debian.pool.ntp.org iburst
#server 2.debian.pool.ntp.org iburst
#server 3.debian.pool.ntp.org iburst
server 192.168.1.2
...
Restart the NTP daemon to use the new configuration:
$ sudo service ntp restart
Once you’ve got a Pi running the Compound Pi daemon successfully, shut it down and place its SD card in any Linux machine with an SD card reader. Unmount any partitions that auto-mount, then figure out which device node represents the SD card. For example, the following would tell you that the SD card is sdd:
$ dmesg | tail | grep "Attached SCSI removable disk"
[ 3.428459] sd 8:0:0:0: [sdd] Attached SCSI removable disk
Clone the SD card into a disk file:
$ sudo dd if=/dev/sdd of=server.img bs=1M
This will take some considerable time to finish. Once it has done so, eject the source SD card and insert the target one in its place. Remember to unmount any partitions which auto-mount, then execute the reverse command:
$ sudo dd if=server.img of=/dev/sdd bs=1M
Repeat this last step for all remaining target cards. Finally, install the SD cards in your set of Pi servers and boot them all to ensure their camera modules activate.
Warning
Ensure your target SD cards are the same size or larger than the source SD card. If they are larger, they will still appear the same size as the source after cloning because you the cloning also duplicates the partition table of the smaller device.
Back on the Ubuntu client machine, execute cpi to run the client. You will be presented with a command line like the following:
CompoundPi Client version 0.4
Type "help" for more information, or "find" to locate Pi servers
cpi>
Firstly, ensure that the network configuration is correct. The config command can be used to print the current configuration:
cpi> config
Setting Value
------------------- --------------
network 192.168.0.0/16
port 5647
bind 0.0.0.0:5647
timeout 15
capture_delay 0.0
capture_quality 85
capture_count 1
video_port False
record_delay 0.0
record_format h264
record_quality 0
record_bitrate 17000000
record_motion False
record_intra_period 30
time_delta 0.25
output /tmp
warnings False
Assuming we’re using a typical home router which gives out addresses in the 192.168.1.x network, this is incorrect. In order for broadcasts to work, the network must have the correct definition - it’s no good having a superset configured (192.168.0.0/16 is a superset of 192.168.1.0/24). See IPv4 subnetting for more information about subnet configuration.
To correct the network definition, use the set command:
cpi> set network 192.168.1.0/24
cpi> config
Setting Value
------------------- --------------
network 192.168.1.0/24
port 5647
bind 0.0.0.0:5647
timeout 15
capture_delay 0.0
capture_quality 85
capture_count 1
video_port False
record_delay 0.0
record_format h264
record_quality 0
record_bitrate 17000000
record_motion False
record_intra_period 30
time_delta 0.25
output /tmp
warnings False
To make permanent configuration changes, simply place them in a file named ~/.cpi.ini like so:
[cpi]
network=192.168.1.0/24
timeout=10
output=~/Pictures
With the network configured correctly, you can now use find to locate your servers. If you run find on its own it will send out a broadcast ping and wait for a fixed number of seconds for servers to respond. If you know exactly how many servers you have, specify a number with the find command and it will warn you if it doesn’t find that many servers (it will also finish faster if it does find the expected number of Pis):
cpi> find 2
Found 2 servers
You can query the status of your servers with the status command which will give you the basics for the camera configuration, the time according to the server, and the number of images currently stored in memory on the server. If you only want to query a specific set of servers you can give their addresses as a parameter:
cpi> status 192.168.1.154
Address Mode AGC AWB Exp Meter Flip Clock #
------------- ----------- -------------- -------------- -------------- ------- ---- -------------- -
192.168.1.154 1280x800@30 auto (1.0,1.0) auto (1.6,1.3) auto (28.48ms) average none 0:00:00 0
If any major discrepancies are detected (resolution, framerate, timestamp, etc.), the status command should notify you of them. The maximum discrepancy permitted in the timestamp is configured with the time_delta configuration setting.
To shoot an image, use the capture command:
cpi> capture
Finally, to download the captured images from all Pis, simply use the download command:
cpi> download
Downloaded image 0 from 192.168.1.154
Downloaded image 0 from 192.168.1.168
You can use the config and set commands to configure capture options, the download target directory, and so on.
Since version 0.3 a GUI client is also provided. The basic operations of the GUI client are essentially the same as the command line client, the only major difference being that download is performed automatically after capture. You can start the GUI client with the cpigui command.
Once you have images captured from your array of Pi servers, you may wish to convert them into video (e.g. for bullet-time effects and such like). The ordering of captured images is currently relatively tricky. However, once you have your images in an order that you like you can use the following ffmpeg command line to convert the series of JPEGs into an MP4 with H.264 encoding:
ffmpeg -y -f image2 -i frame%03d.jpg -r 24 -vcodec libx264 -profile high -preset slow output.mp4
The above command line assumes that your images are all named something like frame001.jpg or frame027.jpg and that they are in advancing numerical order. It also assumes that you wish the output to be called output.mp4. x264 compression is quite computationally intensive, so this is something you want to do on a platform with a fair amount of power (like a full PC).
Compound Pi provides some crude but effective tools for debugging problems. The first is simply that the daemon activates the camera by default. If you see a Pi server without the camera LED lit after boot-up, you know the daemon has failed to start for some reason.
The identify command is the main debugging tool provided by Compound Pi. If specified without any further parameters it will cause all discovered Pi servers to blink their camera LED for 5 seconds. Thus, if you run this command immediately after find you can quickly locate any Pi servers that were not discovered (typically this is due to misconfiguration of the network).
If identify is specified with one or more addresses, it will blink the LED on the specified Pi servers. This can be used to quickly figure out which address corresponds to which Pi (useful when dynamic addressing is used).