RealSenseSDK2で任意の場所の距離を取得する

距離を自由に扱いたいので、まず任意の場所の距離を取得したいと思います。
今回は画像の真ん中の座標の距離を取得します。

#include <stdio.h>
#include <librealsense2/rs.hpp> // Include RealSense Cross Platform API
#include <opencv2/opencv.hpp>   // Include OpenCV API

int main(int argc, char * argv[]) try
{
    // Declare depth colorizer for pretty visualization of depth data
    rs2::colorizer color_map;

    // Declare RealSense pipeline, encapsulating the actual device and sensors
    rs2::pipeline pipe;
    // Start streaming with default recommended configuration
    pipe.start();

    using namespace cv;
    const auto window_name = "Display Image";
    namedWindow(window_name, WINDOW_AUTOSIZE);
    float pixel_distance_in_meters;
    while (waitKey(1) < 0 && cvGetWindowHandle(window_name))
    {
        rs2::frameset data = pipe.wait_for_frames(); // Wait for next set of frames from the camera
        rs2::frame depth = color_map(data.get_depth_frame());
        rs2::depth_frame depth_point = data.get_depth_frame();

        // Query frame size (width and height)
        const int w = depth.as<rs2::video_frame>().get_width();
        const int h = depth.as<rs2::video_frame>().get_height();

        // Create OpenCV matrix of size (w,h) from the colorized depth data
        Mat image(Size(w, h), CV_8UC3, (void*)depth.get_data(), Mat::AUTO_STEP);

        //get depth
        //画像の真ん中のxy座標の距離を取得
        pixel_distance_in_meters = depth_point.get_distance(w/2,h/2);
        std::cout << pixel_distance_in_meters  << std::endl;

        // Update the window with new data
        imshow(window_name, image);
    }

    return EXIT_SUCCESS;
}
catch (const rs2::error & e)
{
    std::cerr << "RealSense error calling " << e.get_failed_function() << "(" << e.get_failed_args() << "):\n    " << e.what() << std::endl;
    return EXIT_FAILURE;
}
catch (const std::exception& e)
{
    std::cerr << e.what() << std::endl;
    return EXIT_FAILURE;
}

参考

Projection in RealSense SDK 2.0 · IntelRealSense/librealsense Wiki · GitHub