OpenCV 3.2 Viz 3D可视化

该可视化模块提供了坐标系变化，3D动画等功能

最简单的显示坐标系

  viz::Viz3d window("window");
  window.showWidget("Coordinate", viz::WCoordinateSystem());
  window.spin();

其中spin()函数开启一个event loop永远循环，spinOnce(int time = 1, bool redraw = true)表示event loop循环time时间。通常将与视图的交互放在一个循环中：

  while(!window.wasStopped())
  {
    // interact with window
    window.spinOnce(1, true);
  }

3D姿态通常通过仿射变换Affine3f来指定， 可以利用罗德里格斯公式将较为直观的旋转向量转换为旋转矩阵，带入放射变化中：

#include <iostream>
#include <opencv2/viz.hpp>
#include <opencv2/highgui.hpp>
#include <opencv2/calib3d.hpp>

using namespace std;
using namespace cv;

int main()
{
  viz::Viz3d window("window");
  window.showWidget("Coordinate", viz::WCoordinateSystem());
  
  viz::WPlane plane(Size2d(2,2), viz::Color::white());
  plane.setRenderingProperty(viz::LINE_WIDTH, 5);
  plane.setPose(Affine3f());
  window.showWidget("plane", plane);
  
  Mat rvec = Mat::zeros(1, 3, CV_32F);
  while(!window.wasStopped())
  {
    rvec.at<float>(0,0) = 0.f;
    rvec.at<float>(0,1) += CV_PI*0.01f;
    rvec.at<float>(0,2) = 0.f;
    Mat rmat;
    Rodrigues(rvec, rmat);
    Affine3f pose(rmat, Vec3f(0,0,0));
    window.setWidgetPose("plane", pose);
    window.spinOnce(1, true);
  }
}

实现了一个xy平面上，白色的2*2大小平面绕y轴旋转的动画

Viz模块中主要使用Affine3f仿射变换来处理空间转换的过程，下面实例实现3D点云在世界坐标系下，绕相机坐标系z轴旋转：

#include <iostream>
#include <fstream>
#include <opencv2/viz.hpp>
#include <opencv2/highgui.hpp>
#include <opencv2/calib3d.hpp>

using namespace std;
using namespace cv;


// load a ply file
// http://graphics.stanford.edu/data/3Dscanrep/
Mat cvcloud_load()
{
    Mat cloud(1, 1889, CV_32FC3);
    ifstream ifs("/home/shang/Desktop/bunny.ply");

    string str;
    for(size_t i = 0; i < 12; ++i)
        getline(ifs, str);

    Point3f* data = cloud.ptr<cv::Point3f>();
    float dummy1, dummy2;
    for(size_t i = 0; i < 1889; ++i)
        ifs >> data[i].x >> data[i].y >> data[i].z >> dummy1 >> dummy2;

    cloud *= 5.0f;
    return cloud;
}

int main()
{
  // step 1. construct window
  viz::Viz3d window("mywindow");
  window.showWidget("Coordinate Widget", viz::WCoordinateSystem());
  
  
  // step 2. set the camera pose
  Vec3f cam_position(3.0f, 3.0f, -3.0f), cam_focal_point(3.f, 3.f, -4.0f), cam_y_direc(-1.0f,0.0f,0.0f);
  Affine3f cam_pose = viz::makeCameraPose(cam_position, cam_focal_point, cam_y_direc);
  Affine3f transform = viz::makeTransformToGlobal(Vec3f(0.0f,-1.0f, 0.0f), Vec3f(-1.0f, 0.0f, 0.0f), Vec3f(0.0f, 0.0f, -1.0f), cam_position);
  
  
  Mat bunny = cvcloud_load();
  viz::WCloud bunny_cloud(bunny,viz::Color::green());
  
  double z = 0.0f;
  Affine3f cloud_pose_global;
  while(!window.wasStopped())
  {
    z += CV_PI*0.01f;
    cloud_pose_global = transform.inv()*Affine3f(Vec3f(0.0, 0.0, z), Vec3f(0.0, 0.0, 2.0))*Affine3f::Identity();
    window.showWidget("bunny_cloud", bunny_cloud, cloud_pose_global);
    
    // step 3. To show camera and frustum by pose
    // scale is 0.5
    viz::WCameraPosition camera(0.5);
    // show the frustum by intrinsic matrix
    viz::WCameraPosition camera_frustum(Matx33f(3.1,0,0.1,0,3.2,0.2,0,0,1));
    window.showWidget("Camera", camera, cam_pose);
    window.showWidget("Camera_frustum", camera_frustum, cam_pose);
    window.spinOnce(1, true);
  }
  return 0;
}