Using Multiple Cameras

Switching the Driver Views

If you’re interested in just switching what the driver sees, you can change the camera used by the camera server dynamically. If you open a stream viewer nominally to camera1, the robot code will change the stream contents to either camera1 or camera2 based on the joystick trigger.

JAVA

UsbCamera camera1;
UsbCamera camera2;
VideoSink server;
Joystick joy1 = new Joystick(0);

public Robot() {
    camera1 = CameraServer.startAutomaticCapture(0);
    camera2 = CameraServer.startAutomaticCapture(1);
    server = CameraServer.getServer();
}
@Override
public void teleopPeriodic() {
    if (joy1.getTriggerPressed()) {
        System.out.println("Setting camera 2");
        server.setSource(camera2);
    } else if (joy1.getTriggerReleased()) {
        System.out.println("Setting camera 1");
        server.setSource(camera1);
    }
}

C++

wpi::cs::UsbCamera camera1;
wpi::cs::UsbCamera camera2;
wpi::cs::VideoSink server;
wpi::Joystick joy1{0};
bool prevTrigger = false;
Robot() {
  camera1 = wpi::CameraServer::StartAutomaticCapture(0);
  camera2 = wpi::CameraServer::StartAutomaticCapture(1);
  server = wpi::CameraServer::GetServer();
}
void TeleopPeriodic() override {
  if (joy1.GetTrigger() && !prevTrigger) {
    std::cout << "Setting Camera 2" << std::endl;
    server.SetSource(camera2);
  } else if (!joy1.GetTrigger() && prevTrigger) {
    std::cout << "Setting Camera 1" << std::endl;
    server.SetSource(camera1);
  }
  prevTrigger = joy1.GetTrigger();
}

PYTHON

# Setting the source directly via joystick isn't possible in Python, you
# should use NetworkTables as shown above instead

Keeping Streams Open

By default, the cscore library is pretty aggressive in turning off cameras not in use. What this means is that when you switch cameras, it may disconnect from the camera not in use, so switching back will have some delay as it reconnects to the camera. To keep both camera connections open, use the SetConnectionStrategy() method to tell the library to keep the streams open, even if you aren’t using them.

Java

UsbCamera camera1;
UsbCamera camera2;
VideoSink server;
Joystick joy1 = new Joystick(0);

public Robot() {
    camera1 = CameraServer.startAutomaticCapture(0);
    camera2 = CameraServer.startAutomaticCapture(1);
    server = CameraServer.getServer();
    camera1.setConnectionStrategy(ConnectionStrategy.kKeepOpen);
    camera2.setConnectionStrategy(ConnectionStrategy.kKeepOpen);
}
@Override
public void teleopPeriodic() {
    if (joy1.getTriggerPressed()) {
        System.out.println("Setting camera 2");
        server.setSource(camera2);
    } else if (joy1.getTriggerReleased()) {
        System.out.println("Setting camera 1");
        server.setSource(camera1);
    }
}

C++

wpi::cs::UsbCamera camera1;
wpi::cs::UsbCamera camera2;
wpi::cs::VideoSink server;
wpi::Joystick joy1{0};
bool prevTrigger = false;
Robot() {
  camera1 = wpi::CameraServer::StartAutomaticCapture(0);
  camera2 = wpi::CameraServer::StartAutomaticCapture(1);
  server = wpi::CameraServer::GetServer();
  camera1.SetConnectionStrategy(cs::VideoSource::ConnectionStrategy::kConnectionKeepOpen);
  camera2.SetConnectionStrategy(cs::VideoSource::ConnectionStrategy::kConnectionKeepOpen);
}
void TeleopPeriodic() override {
  if (joy1.GetTrigger() && !prevTrigger) {
    std::cout << "Setting Camera 2" << std::endl;
    server.SetSource(camera2);
  } else if (!joy1.GetTrigger() && prevTrigger) {
    std::cout << "Setting Camera 1" << std::endl;
    server.SetSource(camera1);
  }
  prevTrigger = joy1.GetTrigger();
}

PYTHON

Note

Python requires you to place your image processing code in a separate file from your robot code. You can create robot.py and vision.py in the same directory.

robot.py contents:

import wpilib
from ntcore import NetworkTableInstance
class MyRobot(wpilib.TimedRobot):
    def robotInit(self):
        self.joy1 = wpilib.Joystick(0)
        self.cameraSelection = NetworkTableInstance.getDefault().getTable("").getEntry("CameraSelection")
        wpilib.CameraServer.launch("vision.py:main")
    def teleopPeriodic(self):
        if self.joy1.getTriggerPressed():
            print("Setting camera 2")
            self.cameraSelection.setString("USB Camera 1")
        elif self.joy1.getTriggerReleased():
            print("Setting camera 1")
            self.cameraSelection.setString("USB Camera 0")

vision.py contents:

from cscore import CameraServer, VideoSource
    def main():
    CameraServer.enableLogging()
    camera1 = CameraServer.startAutomaticCapture(0)
    camera2 = CameraServer.startAutomaticCapture(1)
    camera1.setConnectionStrategy(VideoSource.ConnectionStrategy.kConnectionKeepOpen)
    camera2.setConnectionStrategy(VideoSource.ConnectionStrategy.kConnectionKeepOpen)
        CameraServer.waitForever()

pyproject.toml contents (this only shows the portions you need to update):

[tool.robotpy]
...
# Add cscore to the robotpy-extras list
robotpy_extras = ["cscore"]

Note

If both cameras are USB, you may run into USB bandwidth limitations with higher resolutions, as in all of these cases the roboRIO is going to be streaming data from both cameras to the roboRIO simultaneously (for a short period in options 1 and 2, and continuously in option 3). It is theoretically possible for the library to avoid this simultaneity in the option 2 case (only), but this is not currently implemented.

Different cameras report bandwidth usage differently. The library will tell you if you’re hitting the limit; you’ll get this error message:

could not start streaming due to USB bandwidth limitations;
try a lower resolution or a different pixel format
(VIDIOC_STREAMON: No space left on device)

If you’re using Option 3 it will give you this error during the Robot constructor. Thus you should just try your desired resolution and adjusting as necessary until you both don’t get that error and don’t exceed the radio bandwidth limitations.