Parallel Capturing and Processing

This topic explains how to run image acquisition and 3d data computation independently when using a single camera.

Please read the topics Opening a Camera and Grabbing 3D Data first.

Note

Rendering commands like RenderPointMap and RenderView use a single OpenGL context and therefore will be internally serialized and run sequentially, also when executed from separate Execute nodes. As these commands also have a single, global output node it is recommended to run at most one instance of each at a time.

Code Examples

Single Threaded

C++

// Call the Open command to open the camera
NxLibCommand open(cmdOpen);
open.parameters()[itmCameras] = "1234";
open.execute();

// Create persistent command objects with two new, separate execution slots "capture" and "compute" under /Execute
// Create a new execution node "capture" under /Execute, to asynchronously run the cmdCapture command.
NxLibCommand capture(cmdCapture, "capture");

// Create a new execution node "compute" under /Execute, to asynchronously run the
// cmdComputeDisparityMap command.
NxLibCommand computeDisparityMap(cmdComputeDisparityMap, "compute");

// Note: the two command objects capture and computeDisparityMap now created two separate execution nodes
// /Execute/capture and /Execute/compute. Each of these nodes has its own Command, Parameters and Result subnodes
// and can be used to execute any command independently from commands any other execution slot.

// Note: when creating new execution slots their parameters will not be cleared after command execution and can be
// reused for the next execution in this slot
capture.parameters()[itmTimeout] = 200; // Set a capture timeout of 200ms

int numImagesCaptured = 0;
int numDisparityMapsComputed = 0;

// start the first capture command before entering the loop
capture.execute(false);
while (numImagesCaptured < 50) { // run loop until 50 images have been captured
	if (capture.finished()) {    // check if the capture operation is already done
		if (capture.successful()) numImagesCaptured++;
		capture.execute(false); // start the next image acquisition
	}
	if ((numImagesCaptured > 0) &&
	    computeDisparityMap
	        .finished()) { // check if we already have an image and the last disparity map computation is finished
		numDisparityMapsComputed++;
		computeDisparityMap.execute(false); // start the next disparity map computation
	}
}
printf("Captured %d images and computed %d disparity maps.\n", numImagesCaptured, numDisparityMapsComputed);

Multi Threaded

Note

The two command objects capture and computeDisparityMap in Thread 1 and Thread 2 create two separate execution nodes /Execute/capture and /Execute/compute. Each of these nodes has its own Command, Parameters and Result subnodes and can be used to execute any command independently from commands any other execution node.

C++

Preparation (e.g. in main thread):

// Call the Open command to open the camera
NxLibCommand open(cmdOpen);
open.parameters()[itmCameras] = "1234";
open.execute();

// capture one image synchronously so that the computation thread has an initial image to process
NxLibCommand(cmdCapture).execute();

// ... start thread 1 and thread 2 now

Thread 1 (capturing):

// Create command object working in a separate execution slot "capture" under /Execute
NxLibCommand capture(cmdCapture, "capture");

// Note: when creating new execution slots their parameters will not be cleared after command execution and can
// be reused for the next execution in this slot
capture.parameters()[itmTimeout] = 200; // Set a capture timeout of 200ms
int numImagesCaptured = 0;

while (numImagesCaptured < 50) { // run loop until 50 images have been captured
	capture.execute();
	numImagesCaptured++;
}

Thread 2 (disparity map computation):

// Create command object working in a separate execution slot "compute" under /Execute
NxLibCommand compute(cmdComputeDisparityMap, "compute");

int numDisparityMapsComputed = 0;

while (numDisparityMapsComputed < 50) { // run loop until 50 images have been processed
	compute.execute();
	numDisparityMapsComputed++;
}