Implement the optical flow algorithm for radar precipitation

[NigelRoberts]

Stephen Moseley as Nowcasting Lead Scientist wants to have the capability to extrapolate radar precipitation rate fields forward in time to use for nowcasting.

Related issues: Part I #167. Part II #168. Part III #169.

• [x] Part I #167 contains:

  • Method to derive advection velocities using Martina's STEPS Python optical flow method (see Stephen's homespace from_Martina/Decomposition_2017.py: Class OFC (550 lines))
  • Method to derive advection velocities using OpenCV optical flow code. flow = cv2.calcOpticalFlowFarneback(frame1, frame2, 0.5, 3, 15, 3, 5, 1.2, 0)
  • Demonstrate difference in advection velocities between these two methods.

• [ ] Part II #168 contains:

  • Method to derive the mean advection velocities between two consecutive pairs of data (time 1 -> time 2 and time 2 -> time 3).
  • Method to calculate orographic precipitation enhancement (porting steps_core_orogenh.cpp method ComputeEnhancements).
  • Method to create an extrapolation forecast using advection velocities.

• [ ] Part III #169 contains:

  • Method to insert or remove the impact of orographic precipitation enhancement from STEPS ComputeEnhancements C++ method.
  • Modify method to create an extrapolation forecast using advection velocities to use orographic enhancement data.

Acceptance criteria:

• Have plugin(s) which can use these algorithms.
• Unit testing
• Demonstration showing how the two orographic enhancement methods compare.

[fionaRust]

No longer using these epics and all outstanding work is covered by other tickets so closing.