# # # OPTFLOW_USE_INITIAL_FLOW uses initial estimations, stored in nextPts; if the flag is not set, then prevPts is copied to nextPts and is considered the initial estimate.
# # opticalFlowNextPts, status, err = cv.calcOpticalFlowPyrLK(
# #     prevImg_gray, nextImg_gray, prevPts2f, nextPts2f, cv.OPTFLOW_USE_INITIAL_FLOW)

# OPTFLOW_USE_INITIAL_FLOW
# https://docs.opencv.org/3.4/dc/d6b/group__video__track.html#
