Enable OpenCV4 compability

modules/MeasureOpticalFlowDualTVL1.cpp

@@ -23,6 +23,9 @@
  */
 
 #include "MeasureOpticalFlowDualTVL1.h"
+#if CV_MAJOR_VERSION >= 4
+#include <opencv2/optflow.hpp>
+#endif
 
 using cv::Mat;
 using cv::Mat_;
@@ -61,7 +64,11 @@ bool MeasureOpticalFlowDualTVL1::create( std::vector<CalypFrame*> apcFrameList )
       return false;
 
   m_iStep = 16;
+  #if CV_MAJOR_VERSION >= 4
+  m_cTvl1 = cv::optflow::createOptFlow_DualTVL1();
+  #else
   m_cTvl1 = cv::createOptFlow_DualTVL1();
+  #endif
   m_pcOutputFrame = new CalypFrame( apcFrameList[0]->getWidth(), apcFrameList[0]->getHeight(), CLP_GRAY );
 
   return true;