title: StereoBm Opencv function gives an error "object of an abstract class cannot be defined"
body: <p>When I intialise StereoBM object I get an error "object of an abstract class cannot be defined". I checked calib3d.hpp and I found that StereoBM is an abstract class. Please provide me a solution how to define all those functions in StereoBM class</p>
  
  <pre><code>cv::Mat leftimg =cv::imread("leftimage.jpg");
  cv::Mat rightimg = cv::imread("rightimage.jpg");
  cv::Size imagesize = leftimg.size();
  
  cv::Mat g1,g2,disp,disp8;
  cv::cvtColor(leftimg,g1,cv::COLOR_BGR2GRAY);
  cv::cvtColor(rightimg,g2,cv::COLOR_BGR2GRAY);
  
  cv::StereoBM *sbm;    
  sbm-&gt;setDisp12MaxDiff(1);
  sbm-&gt;setSpeckleRange(8);
  sbm-&gt;setSpeckleWindowSize(0);
  sbm-&gt;setUniquenessRatio(0);
  sbm-&gt;setTextureThreshold(507);
  sbm-&gt;setMinDisparity(-39);
  sbm-&gt;setPreFilterCap(61);
  sbm-&gt;setPreFilterSize(5);
  sbm-&gt;compute(g1,g2,disp);
  normalize(disp, disp8, 0, 255, CV_MINMAX, CV_8U);
  
  cv::imshow("left", leftimg);
  cv::imshow("right", rightimg);
  cv::imshow("disp", disp8);
  </code></pre>