Custom Parameter Image Service for a Web Cam

This example program demonstrates how to host an image service that contains an image source with custom parameters. The custom parameters enable developers to extend the given image source API with additional functionality. To demonstrate, the image source in this example contains a custom parameter that enable clients to specify the contrast of the image the service returns.

This example can be run on an external computer or on a payload such as the CORE I/O. If running on a payload, this example will register the service from a payload, therefore it will require knowing the guid, secret, and IP address of the computer the service will be running off of. See the self registration payloads example for a higher level overview of how to set up and register a payload, as well as how to register a simple announcing service.


This example requires bosdyn API and client to be installed, and must be run using python3. Using pip, these dependencies can be installed using:

python3 -m pip install -r requirements.txt

The example requires OpenCV, which may need to be installed separately following instructions from OpenCV, if installation via pip fails. Alternatively, the example provides a Dockerfile which can be used to build and then run the example.

Example Execution

This example will run the web cam image service locally and register it with the robot’s directory service using a directory keep alive. After running the example clients will be able to send requests to this service through the robot.

(NOTE: the example may need to be run with sudo to enable access to the web cam.)

To run the example from this directory on a payload computer, issue the command:

python3 payload {ROBOT_IP} --guid {PAYLOAD_GUID} --secret {SECRET} --host-ip {PAYLOAD_IP} --port {PORT} --device-name {CAMERA}

To run the example from this directory on an external computer, issue the command:

python3 external {ROBOT_IP} --host-ip {COMPUTER_IP} --port {PORT} --device-name {CAMERA}

The example can be safely exited by issuing a SIGINT (Ctrl + C) to the caller.

This example takes two different IP addresses as arguments. The --host-ip argument describes the IP address for the computer that will be running the web cam image service. A helper exists to try to determine the correct IP address. This command must be run on the same computer that will be running the web cam image service:

python3 -m bosdyn.client {ROBOT_IP} self-ip

The other IP address is the traditional robot hostname (”ROBOT_IP”) argument, which describes the IP address of the robot hosting the directory service.

When launching the web cam image service, the different device names should be provided. All of these sources should be queryable from the web cam image service using OpenCV. They can be specified individually by using the argument --device-name, and appending multiple of the argument to specify each camera source. For example, --device-name CAMERA1 --device-name CAMERA2. By default, the device “0” will be used, which represents the device at index 0 and will connect to the first connected video device found for each operating system. A user can provide either an index to a specific camera device, or the file path to describe the USB location of the camera. Each device will be listed by the service as an image source using the final part of the device name after the last “/” in a filepath (e.g. “/dev/video0” will result in an image source name “video0”, device index “0” will also have image source name “video0”). Note for linux, by default the camera devices connected will have a filepath formatted as /dev/videoXXX where “XXX” is the index of the camera. However, on Windows the default locations are more difficult to determine, so providing the index number as the device name is preferred.

If this example is run on a payload computer, it requires a GUID (uniquely generated payload specifier) and secret (private string associated with a payload) for a registered and authorized payload computer as arguments when launching the example. This “payload” can represent any type of computer capable of hosting the web cam image service. See documentation on configuration of payload software for more information.

A port number for the image service can be specified using the --port argument. It is possible to bypass the port argument and allow a random port number to be selected, but it is discouraged since restarts may result in unexpected changes to a services listening port. This port number will be used with the host-ip (”PAYLOAD_IP”) to fully specify where the image service is running. This port number must be open and cannot be blocked by a local firewall, otherwise the web cam image service will be unreachable from the robot and the directory registration service.

There is an optional string argument --codec to specify a four character video codec describing the camera’s compression/decompression software. The video codec code is operating system dependent. For example, on a Windows computer, the video codec is commonly ‘DIVX’, and on a linux computer, the video codec is commonly ‘MJPG’. Note, the video codec does not necessarily need to be specified as OpenCV’s default selection will typically work for most web cams, however if you are seeing OpenCV errors when the image service tries to capture an image, then try specifying the video codec for your camera. An example error of this type is:

[ WARN:0] global /io/opencv/modules/videoio/src/cap_v4l.cpp (998) tryIoctl VIDEOIO(V4L2:/dev/video1): select() timeout.

This error was fixed for a linux experiment by providing the video codec argument as --codec mjpg.

There are optional arguments to change the camera’s resolution if it is possible. The arguments --res-width and --res-height can adjust the image resolution for all captures completed by the service. If the input resolution is not achievable by the camera, the nearest/most similar resolution will be chosen and used. If no resolution is provided, the image service will use the camera’s defaults.

Lastly, the command line argument --show-debug-info will allow a user to live-view the OpenCV output of the web cam video capture on their local computer. Only use this flag for debug purposes, as it will likely slow down the main example operation and reduce the performance of the image service.

Debugging Tips

Here are a couple suggestions for debugging the example:

  • Ensure the camera is powered on and plugged in.

  • Check that your web cam is working separate from the api connections. For linux, the program Cheese allows you to stream from the camera. Run cheese /dev/video0 (or the name of your cameras USB location) to verify the image appears.

  • Use the command line argument --show-debug-info which will display the openCV capture output before encoded it into the image service protobuf message. If the image is unable to show here, then the device name is likely incorrect or unreachable.

  • Check that the image service appears in the directory using the command line tool: python3 -m bosdyn.client {ROBOT_IP} dir list

  • Use the image service tester program to ensure the service can successfully be communicated with and that each RPC will complete correctly.

  • When all tests pass for the image service tester program, check that the tablet is detecting the web cam image service by looking in the camera sources drop down menu (top-left of the status bar) and then check that the images are appearing by selecting the “Web Cam” camera source.

Run the Custom Parameter Image Service using Docker

Please refer to this document for general instructions on how to run software applications on computation payloads as Docker containers. The sections below describe how to run the example on a CORE I/O payload, locally on a development environment, or a SpotCORE payload.


Spot Extensions are the recommended way to deploy applications that run on the CORE I/O. The example contains a helper script to build Spot Extensions easily. To build a Spot Extension for this example, navigate to the directory containing this README and run the following command:

python3 ../../extensions/ \
    --dockerfile-paths Dockerfile.l4t \
    --build-image-tags custom_parameter_image_server:l4t \
    -i custom_parameter_image_server.tar.gz \
    --package-dir . \
    --spx custom_parameter_image_server.spx


To build the image:

sudo docker build -t custom_parameter_image_server:local -f Dockerfile .

To run a container:

sudo docker run -it --device /dev/video0 --network=host custom_parameter_image_server:local payload --host-ip localhost --port 50051 --guid GUID --secret SECRET ROBOT_IP

where GUID and SECRET are for an Authorized payload (see above) and ROBOT_IP is the robot’s IP address.

SpotCORE (Deprecated)

  • The application arguments needed to run the Web Cam application in this example are --device-name DEVICE_NAME --guid GUID --secret SECRET --host-ip HOST_COMPUTER_IP --port PORT_NUMBER ROBOT_IP

  • In the Runtime & Resources tab in the Portainer container configuration page , click add device and specify the camera’s communication port (e.g. /dev/video0) in both the host field as well as the container field before deploying the container.

  • If running the docker container locally, the device needs to be mapped from the container to your local computer in a similar manner to how it is configured on portainer. The docker run command needs the additional argument --device=/dev/video0:/dev/video0, which is mapping the host location to the container location with /dev/video0 as an example.