Capturing Images with Hardware Trigger

When working with hardware trigger you need to make sure that the camera is continuously armed and waiting for a new trigger signal in order to not miss any trigger edges. The pseudo code opens a camera, enables hardware trigger and captures and processes a fixed number of images.

Code Examples

Using the Trigger and Retrieve commands and a polling wait loop

C++Halcon/HDevelop

NxLibItem root; // References the tree's root item at path "/"

auto const serial = "1234"; // Replace with your camera's serial number

// References the camera's item at path "/Cameras/BySerialNo/<Serial Number>"
NxLibItem camera = root[itmCameras][serial];

// Call the Open command to open the camera
// Note: the variable name 'open' does not matter; the constant 'cmdOpen' specifies the name of the command to be
// executed when '.execute()' is called on the object.
NxLibCommand open(cmdOpen);
// Set parameters for the command
open.parameters()[itmCameras] = serial;
open.execute();

// Set the camera to trigger on a falling edge on the GPIO port
camera[itmParameters][itmCapture][itmTriggerMode] = valFallingEdge; // the default for TriggerMode is "Software"

for (int imageIndex = 0; imageIndex < 10; imageIndex++) {
	// Trigger cameras that are not yet armed and waiting for a hardware trigger (e.g. when taking the first image).
	// With default settings this will trigger untriggered cameras only.
	NxLibCommand(cmdTrigger).execute();

	// Call Retrieve in a loop to poll for newly arrived images; you could also use the Timeout parameter here if
	// you don't want to poll
	NxLibCommand retrieve(cmdRetrieve);
	while (true) {
		retrieve.parameters()[itmTimeout] = 0;
		retrieve.execute();
		if (retrieve.result()[serial][itmRetrieved].asBool()) {
			// A new image has been received and copied into the raw image node
			break;
		}
	}

	// Trigger the camera again, so that it is immediately armed for the next trigger again
	NxLibCommand(cmdTrigger).execute();

	// Compute the disparity map, point map, and process the data according to your needs
}

Using the Capture command and a fixed wait timeout

When using the Capture command the entire trigger, wait and re-arm sequence can be accomplished with a single command:

C++Halcon/HDevelop

for (int imageIndex = 0; imageIndex < 10; imageIndex++) {
	NxLibCommand capture(cmdCapture);
	// Trigger any camera that is not armed yet at the beginning of the command execution
	capture.parameters()[itmInitialTrigger] = valUntriggered;
	capture.parameters()[itmWaitFor] = valTriggered; // Wait for all triggered cameras
	capture.parameters()[itmTimeout] = 10000;        // wait up to 10 seconds
	// After the wait period trigger all cameras again to arm them for the next hardware trigger signal
	capture.parameters()[itmFinalTrigger] = valAll;
	capture.execute(); // Execute the command with the previously specified parameters

	// Compute the disparity map, point map, and process the data according to your needs.
	// ...
}

Note

See Grabbing 3D Data for an example on how to process data according to your needs.

Using the Capture command with a polling loop

You can also use the Capture command to trigger the camera and retrieve images by polling:

C++Halcon/HDevelop

int imageIndex = 0;
while (imageIndex < 10) {
	NxLibCommand capture(cmdCapture);
	// Skip trigger phase 1 at the beginning of the command (see documentatio of the Capture command for a
	// description of the execution phases)
	capture.parameters()[itmInitialTrigger] = valNone;
	// Don't wait for any cameras; the command will still retrieve images in phase 2 if they are ready
	capture.parameters()[itmWaitFor] = valNone;
	// Re-arm all idle cameras again for the next hardware trigger signal
	capture.parameters()[itmFinalTrigger] = valUntriggered;
	// Execute the command with the previously specified parameters
	capture.execute();

	// Check if an image has been retrieved; you need to know the camera serial number ("1234") to query the flags
	// for the camera of interest.
	if (capture.result()["1234"][itmRetrieved].asBool()) {
		// Compute the disparity map, point map, and process the data according to your needs
		// ...
		imageIndex++;
	}
}

Note

• See Capture for a description of the execution phases.

• See Grabbing 3D Data for an example on how to process data according to your needs.