INDI Driver Development

This guide is written with the assumption that you are using the libindi C++ library to write your driver.

Organization of INDI Drivers

The INDI Main Repo includes several default drivers in addition to the main library. These drivers don't require extra libraries to work typically just serial or TCP communication with the hardware. The INDI 3rd Party Repo contains many more drivers that can be developed independently of the main drivers. These may require extra libraries (for instance working with USB cameras) or just have release cycles outside of the slower main library. Having them separate also reduces the size of the main library and it's codebase.

When is a 3rd party driver required?

  • Driver requires external dependencies (other than the indi-core package)
  • Driver requires a separate release cycle
  • Driver has a different license than indi-core

If you want to develop a new driver, it is recommended to create it separate from both, and once you are ready, integrate it into the 3rd party repo.

Driver Construction

Example drivers can be found at in the repo for this documentation.

An INDI driver is what directly communicates with your device(s) hardware. An INDI driver may control one or more hardware devices. It is responsible for controlling the device, and for representing the device properties to clients using INDI's protocol structures. The driver does not contain a main(), as it is expected to operate in an event-driven fashion. The core device class is INDI::DefaultDevice, and it encapsulates the functionality of the most basic INDI device driver.

The driver must implement each ISxxx() function but never calls them. The IS() functions are called by the reference implementation main() as messages arrive from Clients. Within each IS() function the driver performs the desired tasks and then may report back to the Client by calling the IDxxx() functions. The INDI library provides routines for common tasks such as serial communication, string formatting & conversion, and XML parsing. libnova, an external optional library, provides facility for astronomical calculations, while cfitsio provides handling for FITS files.

The reference API provides IExxx() functions to allow the driver to add its own callback functions if desired. The driver can arrange for functions to be called when reading a file descriptor that will not block; when a time interval has expired; or when there is no other client traffic in progress. Several utility functions to search and find INDI vector structs are provides for convenience in the API. The sample indiserver is a stand-alone process that may be used to run one or more INDI-compliant drivers. It takes the name of each driver process to run from its command line arguments. Once a binary driver is compiled, indiserver can load the driver and handle all data steering services between the driver and any number of clients.

The INDI::Telescope, INDI::CCD, INDI::Focuser, and INDI::FilterWheel classes provides the standard interface for those classes of devices. You need to subclass those classes in order to develop a driver for your device. If your device does not belong to those classes (i.e. weather station, or rain detector), then you may subclass INDI::DefaultDevice directly.

The device properties may be either hard-coded in the driver's code, or stored externally in a skeleton file. Which method you opt to utitlize depends on your preferences & devices. Drivers utilizing skeleton files have their properties stored in an XML file (usually under /usr/share/indi in Linux). The skeleton file naming convention is driver_name_sk.xml. For indi_spectracyber it is indi_spectracyber_sk.xml. The contents of the skeleton file is a list of defXXX XML statements enclosed by <INDIDriver> opening and closing tags. Support for automatic auxiliary controls a Driver may add debug, simulation, and configuration controls to the driver by calling addAuxControls(). For each driver, you must provide the device's default name and driver version information.

Tutorial Four is a simple driver to illustrate the skeleton method. Please make sure to install tutorial_four_sk.xml to /usr/share/indi or define INDISKEL envrionment variable to the path of this file before running the tutorial.

INDI Library uses CMake build system, please refer to the CMakeLists.txt file shipped with libindi and 3rd party drivers.

Standard Properties

INDI does not place any special semantics on property names (i.e. properties are just texts, numbers, lights, blobs, or switches that represent no physical function). While GUI clients can construct graphical representation of properties in order to permit the user to operate the device, we run into situations where clients and drivers need to agree on the exact meaning of some fundamental properties.

What if some client need to be aware of the existence of some property in order to perform some function useful to the user? How can that client tie itself to such a property if the property can be arbitrary defined by drivers?

The solution is to define Standard Properties in order to establish a level of interoperability among INDI drivers and clients. We propose a set of shared INDI properties that encapsulate the most common characteristics of astronomical instrumentation of interest.

If the semantics of such properties are properly defined, not only it will insure base interoperability, but complete device automation becomes possible as well. Put another way, INDI standard properties are in essence properties that represent a clearly defined characteristic related to the operation of the device drivers.

For example, a very common standard property is EQUATORIAL_EOD_COORD. This property represents the telescope's current RA and DEC. Clients need to be aware of this property in order to, for example, draw the telescope's cross hair on the sky map. If you write a script to control a telescope, you know that any telescope supporting EQUATORIAL_EOD_COORD will behave in an expected manner when the property is invoked.

INDI clients are required to honor standard properties if when and they implement any functions associated with a particular standard property. Furthermore, INDI drivers employing standard properties should strictly adhere to the standard properties structure as defined here.

General Properties

Name Type Values Description
CONNECTION Switch CONNECT Establish connection to the hardware
    DISCONNECT Disconnect from the hardware
DEVICE_PORT Text PORT Device connection port
TIME_LST Number LST Local sidereal time HH:MM:SS
TIME_UTC Text UTC UTC time in ISO 8601 format
    OFFSET UTC offset, in hours +E
GEOGRAPHIC_COORD Number LAT Site latitude (-90 to +90) degrees +N
    LONG Site longitude (0 to 360) degrees +E
    ELEV Site elevation, meters
    HUMIDITY Percentage %
    UPLOAD_LOCAL Save BLOB locally
    UPLOAD_BOTH Send blob to client and save locally
UPLOAD_SETTINGS Text UPLOAD_DIR Upload directory if BLOB is saved locally
    UPLOAD_PREFIX Prefix used when saving filename
ACTIVE_DEVICES Text ACTIVE_TELESCOPE Name of active devices.

ACTIVE_DEVICES is used to aid clients in automatically providing the users with a list of active devices (i.e. CONNECTION is ON) whenever needed. For example, a CCD driver may define ACTIVE_DEVICES property with one member: ACTIVE_TELESCOPE. Suppose that the client is also running LX200 Basic driver to control the telescope. If the telescope is connected, the client may automatically fill the ACTIVE_TELESCOPE field or provide a drop-down list of active telescopes to select from. Once set, the CCD driver may record, for example, the telescope name, RA, DEC, among other metadata once it captures an image. Therefore, ACTIVE_DEVICES is primarily used to link together different classes of devices to exchange information if required.

Telescope Properties

Telescope standard properties define critical properties for the operation and control of the mount. In addition to the properties below, all properties in INDI Alignment Subsystem are considered standard properties as well and must be reserved in all implementations.

Name Type Values Description
EQUATORIAL_COORD Number   Equatorial astrometric J2000 coordinate
    RA J2000 RA, hours
    DEC J2000 Dec, degrees +N
EQUATORIAL_EOD_COORD Number   Equatorial astrometric epoch of date coordinate
    RA JNow RA, hours
    DEC JNow Dec, degrees +N
TARGET_EOD_COORD Number   Slew Target. Read Only property set once requested EQUATORIAL_EOD_COORD is accepted by driver.
    RA JNow RA, hours
    DEC JNow Dec, degrees +N
HORIZONTAL_COORD Number   topocentric coordinate
    ALT Altitude, degrees above horizon
    AZ Azimuth, degrees E of N
ON_COORD_SET Switch   Action device takes when sent any *_COORD property.
    SLEW Slew to a coordinate and stop upon receiving coordinates.
    TRACK Slew to a coordinate and track upon receiving coordinates.
    SYNC Accept coordinate as current position upon receiving coordinates.
TELESCOPE_MOTION_NS Switch   Move telescope north or south
    MOTION_NORTH Move the telescope toward North.
    MOTION_SOUTH Move the telescope toward South.
TELESCOPE_MOTION_WE Switch   Move telescope west or east
    MOTION_WEST Move the telescope toward West.
    MOTION_EAST Move the telescope toward East.
TELESCOPE_TIMED_GUIDE_NS Number   Timed pulse guide in north/south direction
    TIMED_GUIDE_N Guide the scope north for TIMED_GUIDE_N milliseconds.
    TIMED_GUIDE_S Guide the scope south for TIMED_GUIDE_S milliseconds.
TELESCOPE_TIMED_GUIDE_WE Number   Timed pulse guide in north/south direction
    TIMED_GUIDE_W Guide the scope west for TIMED_GUIDE_W milliseconds.
    TIMED_GUIDE_E Guide the scope east for TIMED_GUIDE_E milliseconds.
TELESCOPE_SLEW_RATE Switch   Multiple switch slew rate.
    SLEW_GUIDE 0.5x to 1.0x sidereal rate or slowest possible speed.
    SLEW_CENTERING Slow speed.
    SLEW_FIND Medium speed.
    SLEW_MAX Maximum speed.
TELESCOPE_PARK Switch   Park and unpark the telescope.
    PARK Park the telescope.
    UNPARK Unpark the telescope.
TELESCOPE_PARK_POSITION Number   Home park position (RA/DEC or AZ/ALT) in degrees or encoder ticks.
    PARK_RA or PARK_AZ RA/AZ park coordinates in degrees or ticks.
    PARK_DEC or PARK_ALT DEC/ALT park coordinates in degrees or ticks.
    PARK_CURRENT Use current coordinates/encoders as home park position.
    PARK_DEFAULT Use driver's default park position.
    PARK_WRITE_DATA Write TELESCOPE_PARK_POSITION and current parking status to file ($HOME/.indi/ParkData.xml)
TELESCOPE_ABORT_MOTION Switch ABORT_MOTION Stop telescope rapidly, but gracefully
    TRACK_SIDEREAL Track at sidereal rate.
    TRACK_SOLAR Track at solar rate.
    TRACK_LUNAR Track at lunar rate.
    TRACK_CUSTOM Custom track rate. This element is optional
    TELESCOPE_APERTURE Telescope aperture, mm
    TELESCOPE_FOCAL_LENGTH Telescope focal length, mm
    GUIDER_APERTURE Guide telescope aperture, mm
    GUIDER_FOCAL_LENGTH Guider telescope focal length, mm
    PIER_EAST Mount on the East side of pier (Pointing West).
    PIER_WEST Mount on the West side of pier (Pointing East).


Setting the ON_COORD_SET property does not cause any action but it prepares the mount driver for the next action when any *_COORD number property is received. For example, to sync the mount, first set switch to SYNC and then send the EQUATORIAL_EOD_COORD with the desired sync coordinates.

The driver can define as many TELESCOPE_SLEW_RATE switches as desirable, but at minimum should implement the four switches above.

For clients that want to implement the GOTO functionality of a telescope, they should expect telescope drivers to define either:

  • EQUATORIAL_EOD_COORD for current Epoch; and/or

CCD Properties

Name Type Values Description
CCD_FRAME Number   CCD frame size.
    X Left-most pixel position
    Y Top-most pixel position
    WIDTH Frame width in pixels
    HEIGHT Frame height in pixels
CCD_TEMPERATURE Number CCD_TEMPERATURE_VALUE CCD chip temperature in degrees Celsius
CCD_COOLER Switch   CCD Cooler control.
    COOLER_ON Turn cooler on
    COOLER_OFF Turn cooler off
    FRAME_LIGHT Take a light frame exposure
    FRAME_BIAS Take a bias frame exposure
    FRAME_DARK Take a dark frame exposure
    FRAME_FLAT Take a flat field frame exposure
CCD_BINNING Number    
    HOR_BIN Horizontal binning
    VER_BIN Vertical binning
    CCD_COMPRESS Compress CCD frame (If FITS, it uses fpack to send a .fz file)
    CCD_RAW Send raw CCD frame
CCD_FRAME_RESET Switch RESET Reset CCD frame to default X,Y,W, and H settings. Set binning to 1x1.
CCD_INFO Number    
    CCD_MAX_X Resolution x
    CCD_MAX_Y Resolution y
    CCD_PIXEL_SIZE CCD pixel size in microns
    CCD_PIXEL_SIZE_X Pixel size X, microns
    CCD_PIXEL_SIZE_Y Pixel size Y, microns
    CCD_BITSPERPIXEL Bits per pixel
CCD_CFA Text   Color Filter Array information if the CCD produces a bayered image. Debayering performed at client side.
    CFA_OFFSET_X CFA X Offset.
    CFA_OFFSET_Y CFA Y Offset.
    CFA_TYPE CFA Filter type (e.g. RGGB).
CCD1 BLOB   CCD1 for primary CCD, CCD2 for guider CCD.
    CCD1 Binary fits data encoded in base64. The CCD1.format is used to indicate the data type (e.g. ".fits")

Most CCD_* properties are also applicable to GUIDER chip, so replace CCD with GUIDER above to define properties for the GUIDER chip, if applicable.

CCD Streaming

Some CCD drivers support streaming and recording of video streams. All the properties defined in StreamManager are considered reserved standard properties. The stream data is sent via the same CCD1 BLOB used for image transmission and therefore it is not possible to stream and send regular CCD captures at the same time.

Name Type Values Description
CCD_VIDEO_STREAM Switch STREAM_ON Turn on video stream
    STREAM_OFF Turn off video stream
STREAMING_EXPOSURE Number STREAMING_EXPOSURE_VALUE Frame exposure values in seconds when streaming.
    STREAMING_DIVISOR_VALUE The divisor is used to skip frames as way to throttle the stream down.
FPS Number   Read Only
    EST_FPS Instant frame rate.
    AVG_FPS Average FPS over 1 second.
RECORD_FILE Text RECORD_FILE_DIR Directory to save the file. It defaults to $HOME/indi__D_
    RECORD_FILE_NAME Recording file name. It defaults to indi_record__T_
RECORD_OPTIONS Switch   Set the desired duration in seconds or total frames required for the recording.
    RECORD_DURATION Duration in seconds.
    RECORD_FRAME_TOTAL Total number of frames required
RECORD_STREAM Switch   Start or Stop the stream recording to a file.
    RECORD_ON Start recording. Do not stop unless asked to.
    RECORD_DURATION_ON Start recording until the duration set in RECORD_OPTIONS has elapsed.
    RECORD_FRAME_ON Start recording until the number of frames set in RECORD_OPTIONS has been captured.
    RECORD_OFF Stops recording.
CCD_FAST_TOGGLE Switch INDI_ENABLED Fast Exposure is used to enable camera to immediately begin capturing the next frames.
CCD_FAST_COUNT Number FRAMES Number of fast exposure captured to take once capture begins.


STREAMING_EXPOSURE_VALUE is advisory only as some streaming devices cannot control the exposure duration.

STREAMING_DIVISOR_VALUE is used to skip frames. By default, a divisor value of 1 does not skip any frames. A value of two would skip every other frame (thereby cutting the FPS in half). A frame is skipped when the number of captured frames % divisor is equal to zero.

RECORD_FILE Recorders are responsible for recording the video stream to a file. The recording file directory and name can be set via the RECORD_FILE property which is composed of RECORD_FILE_DIR and RECORD_FILE_NAME elements. You can specify a record directory name together with a file name. You may use special character sequences to generate dynamic names:

  • D is replaced with the date (‘YYYY-MM-DD')
  • H is replaced with the time (‘hh-mm-ss')
  • T is replaced with a timestamp
  • F is replaced with the filter name currently in use

FAST EXPOSURE Fast Exposure is used to enable camera to immediately begin capturing the next frame once the previous frame data is downloaded from the camera. With Fast Exposure disabled, the driver have to wait until the client initiates the next capture request. To minimize the downtime, Fast Exposure can be enabled to trigger for a specific number of frame in Fast Exposure Count property.

Once the initial capture is started, the driver would continue to capture all necessary frames without waiting for client until the count reaches zero. The Fast Exposure Count is decremented after each fast exposure is complete.

Upload Mode affects Fast Exposure behavior depending on the mode selected. For LOCAL mode, where images are saved locally to disk, Fast Exposure is most efficient. For CLIENT or BOTH modes, the driver have to transmit the data over network to the client. If the upload time exceeds the requested exposure time, then Fast Exposure cannot reliably work and the driver would abort the exposure.

Filter Wheel Properties

Name Type Values Description
FILTER_SLOT Number FILTER_SLOT_VALUE The filter wheel's current slot number. Important: Filter numbers start from 1 to N
FILTER_NAME Text FILTER_NAME_VALUE The filter wheel's current slot name

Focuser Properties

Name Type Values Description
FOCUS_SPEED Number   Select focus speed from 0 to N where 0 maps to no motion, and N maps to the fastest speed possible
    FOCUS_SPEED_VALUE Set focuser speed to SPEED
    FOCUS_OUTWARD Focus outward
FOCUS_TIMER Number FOCUS_TIMER_VALUE Focus in the direction of FOCUS_MOTION at rate FOCUS_SPEED for FOCUS_TIMER_VALUE milliseconds
ABS_FOCUS_POSITION Number FOCUS_ABSOLUTE_POSITION Move to this absolute position.
FOCUS_MAX Number FOCUS_MAX_VALUE Focus maximum travel limit in steps.
FOCUS_REVERSE_MOTION Switch ENABLED Reverse default motor direction
    DISABLED Do not reverse, move motor in the default direction.
FOCUS_ABORT_MOTION Switch ABORT Abort focus motion.
FOCUS_SYNC Number FOCUS_SYNC_VALUE Accept this position as the new focuser absolute position.

Dome Properties

Name Type Values Description
DOME_SPEED Number DOME_SPEED_VALUE Set dome speed in RPM.
DOME_MOTION Switch DOME_CW Move dome Clockwise, looking down
    DOME_CCW Move dome counter clockwise, looking down
DOME_TIMER Number DOME_TIMER_VALUE Move the dome in the direction of DOME_MOTION at rate DOME_SPEED for DOME_TIMER_VALUE milliseconds
ABS_DOME_POSITION Number DOME_ABSOLUTE_POSITION Move dome to DOME_ABSOLUTE_POSITION absolute azimuth angle in degrees.
DOME_ABORT_MOTION Switch ABORT Abort dome motion.
DOME_SHUTTER Switch SHUTTER_OPEN Open dome shutter.
    SHUTTER_CLOSE Close dome shutter.
DOME_GOTO Switch DOME_HOME Go to home position.
    DOME_PARK Go to park position.
DOME_PARAMS Number HOME_POSITION Dome home position in absolute degrees azimuth.
    PARK_POSITION Dome parking position in absolute degrees azimuth.
    AUTOSYNC_THRESHOLD see note below
    DOME_AUTOSYNC_DISABLE Disable dome slaving.
    DOME_SHUTTER_WIDTH Dome shutter width (m).
    DM_NORTH_DISPLACEMENT Displacement to the north of the mount center (m).
    DM_EAST_DISPLACEMENT Displacement to the east of the mount center (m).
    DM_UP_DISPLACEMENT UP displacement of the mount center (m).
    DM_OTA_OFFSET Distance from the optical axis to the mount center (m).


  • AUTOSYNC_THRESHOLD: If dome is slaved, AUTOSYNC_THRESHOLD is the number of acceptable azimuth degrees error between reported and requested dome position. Once the difference between target and current dome positions exceed this value, the dome shall be commanded to move to the target position.