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The Kinematic Network Daemon from Nitrogen Logic's Depth Camera Controller. This application runs in the background to provide a convenient interface for a Kinect camera or similar depth sensor supported by libfreenect. KND has all the core graphics processing code, written in C, while the KNC project provides the web UI, written in Ruby.

The sensor's visible area can be divided into 3D zones with specified dimensions, with knd reporting information about objects within each zone. knd operates at the voxel level, with no blob tracking or skeletal tracking, allowing fast operation on low-powered devices.

The Depth Camera Controller web interface, the Automation Controller logic system, the PC Remote, and any custom integrations use a TCP/IP socket to interact with knd. See the API section below.

knd uses all integer math (with a few carefully chosen approximations and optimizations, such as reciprocal multiplication) to support embedded devices without floating point processors.


Copyright 2011-2018 Mike Bourgeous, licensed under GNU Affero GPLv3. See LICENSE for the complete text of the license.

Why AGPLv3? Because this code is being released for historical preservation and probably shouldn't be used for new development. If you want more permissive terms, just get in touch.



You'll need to install a few Debian/Ubuntu packages:

sudo apt-get install libfreenect-dev libusb-1.0-0-dev libevent-dev

You'll also need to build and install nlutils.


Use the provided Makefile to start a parallel compilation with CMake in an architecture-specific subdirectory:

sudo make install # optional

You can build a Debian package with meta/, which uses package helper scripts from nlutils. See the packaging section of the nlutils README for more info.

PKGDIR=/var/tmp meta/ # default output directory is /tmp


You'll need to cross-compile nlutils and Nitrogen Logic's fork of libfreenect first.

# Build for BeagleBoard
./ neon

# Build for SheevaPlug
./ nofp

You can also cross-build Debian packages, using the aforementioned packaging tools from nlutils. This will require some luck -- as of my last test, one of checkinstall/make/cmake/qemu was segfaulting when trying to build an armel package using checkinstall.

# In nlutils

# In knd


To run knd on your local machine, you need to unload the Video4Linux driver for the Kinect and specify the data directory for knd to use:

sudo rmmod gspca_kinect
mkdir $HOME/.knd/
KND_SAVEDIR=$HOME/.knd/ ./build-$(uname -m)/src/knd

If there is no Kinect camera present, if the current user doesn't have permission to access it, or if the camera takes too long to initialize, knd will not start and an error will be displayed.

On an original Nitrogen Logic Depth Camera Controller, knd is run by, started by a line in /etc/inittab. This line is added by the post-firmware-update script in the knc project. makes sure the V4L driver for the Kinect is not loaded, then runs knd in a loop. knd is designed to exit when anything goes wrong, so this loop recovers from errors (such as a Kinect being unplugged and plugged back in) and keeps knd running.


If a Kinect camera is present, knd provides a machine-friendly TCP/IP command-line interface on port 14308. You can connect with Netcat and get a list of supported commands by typing help (replace localhost with the name of your controller if you are not running locally):

nc localhost 14308

There are some examples of parsing the API in shell scripts in examples/.

Commands with example responses

Parameters to commands are comma-separated without whitespace. Parameters may not contain a comma (so zone names cannot contain commas or newlines).

API responses always start with one line of text. Each line will start with OK for an acknowledgement of a command, ERR if a command was invalid, SUB for a periodic response to the sub command, BRIGHT for a response to the getbright command, DEPTH for a depth frame, VIDEO for a video frame. Multi-line or binary responses will contain the number of lines or number of bytes to read immediately following the response line.

Commands will be run in the order they are received, but some commands trigger the generation of delayed responses. Clients will need to handle any line received at any time, based on its prefix, but OK and ERR lines will always be returned in the order commands were sent.

Multi-value responses (e.g. SUB lines) are a sequence of key-value pairs. String values may optionally be quoted. Lists of key-value pairs may be parsed using the nl_parse_kvp() function from libnlutils. Quoted strings may be processed using the nl_unescape_string() function from libnlutils.

Dimensions for the addzone and subzone commands are in millimeters relative to the depth sensor itself. When looking at the front of the depth sensor, positive X points to the right, positive Y points upward toward the ceiling, and positive Z points away from the sensor toward the room.

  • bye
    OK - Goodbye
  • ver
    OK - Version 2
  • help
    OK - 19 commands (app version 0.1.0)
    bye - Disconnects from the server.
    ver - Returns the server protocol version.
    help - Lists available commands.
    addzone - Adds a new global zone (name, xmin, ymin, zmin, xmax, ymax, zmax).
    setzone - Sets a zone's parameters (name, all, xmin, ymin, zmin, xmax, ymax, zmax or name, [attr], value).
    rmzone - Removes a global zone (name).
    clear - Removes all global zones.
    zones - Lists all global zones.
    sub - Subscribe to global zone updates.
    unsub - Unsubscribe from global zone updates.
    getdepth - Grabs a single 11-bit packed depth image (increments subscription count if already subscribed).
    subdepth - Subscribes to 11-bit packed depth data (count (optional, <=0 means forever)).
    unsubdepth - Unsubscribes from 11-bit packed depth data.
    getbright - Asynchronously returns the approximate brightness within each zone.
    getvideo - Grabs a single video image.
    tilt - Sets or returns the camera tilt in degrees from horizontal.
    fps - Returns the approximate frame rate (updated every 200ms).
    lut - Returns the depth look-up table, or looks up an entry in the table.
    sa - Returns the surface area look-up table, or looks up an entry in the table.
  • addzone Living,1,1,1,2,2,2
    OK - Zone "Living" was added.
  • setzone Zone 6,px_xmin,1
    OK - Zone "Zone 6" attribute "px_xmin" was updated.
  • rmzone Zone 6
    OK - Zone "Zone 6" was removed.
  • clear
    OK - All zones were removed.
  • zones (the version is the zone list version, not the application version)
    OK - 1 zones - Version 9, 0 occupied, peak zone is -1 "[none]"
    xmin=1 ymin=1 zmin=1 xmax=2 ymax=2 zmax=2 px_xmin=0 px_ymin=0 px_zmin=0 px_xmax=20 px_ymax=0 px_zmax=0 negate=0 param=pop on_level=160 off_level=140 on_delay=1 off_delay=1 occupied=0 pop=0 maxpop=1 xc=-1 yc=-1 zc=-1 sa=0 name="Zone2"
  • sub (SUB lines will be received at the start and every time a zone changes)
    OK - Subscribed to global zone updates
    SUB - xmin=1 ymin=1 zmin=1 xmax=2 ymax=2 zmax=2 px_xmin=0 px_ymin=0 px_zmin=0 px_xmax=20 px_ymax=0 px_zmax=0 negate=0 param=pop on_level=160 off_level=140 on_delay=1 off_delay=1 occupied=0 pop=0 maxpop=1 xc=-1 yc=-1 zc=-1 sa=0 name="Zone2"
  • unsub
    OK - Unsubscribed from global zone updates
  • getdepth (other lines may be received before the DEPTH line)
    OK - Requested a single depth frame for delivery as a DEPTH message
    DEPTH - 422400 bytes of raw data follow newline
    [raw data]
  • subdepth
    OK - depth frames will be delivered as DEPTH messages until unsubscribed
    DEPTH - 422400 bytes of raw data follow newline
    [raw data]
  • unsubdepth
    OK - Unsubscribed from depth data
  • getbright (other lines may be received before the BRIGHT line)
    OK - Requested brightness for each zone
    BRIGHT - bright=1536 name="Zone2"
  • getvideo (other lines may be received before the VIDEO line)
    OK - Requested delivery of a video frame
    VIDEO - 307200 bytes of video data follow newline
    [raw data]
  • tilt
    OK - Current tilt is 0 degrees
  • tilt 5
    OK - Requested tilt of 5 degrees
  • fps
    OK - 28 fps


Kinematic Network Daemon - Depth sensor backend server for Nitrogen Logic controllers








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