multi-piece hard windowing vs. phase unwrapping vs. resampling

Problem

1. no way to apply simple phase unwrapping to main thread, because it's broken into individual files, and has to be loaded one at a time.
2. accumulated 2*pi unwrapping
   

Analysis

1. when stitching, we save data based on FOV count; have 1 FOV overlap
2. after stitching, do a thorough truncating for all window files, so that the window-based resampling can start at an integer multiple of sampling period, and consecutive window file will have no resampling overlap.
   1. Prev window-file 1: truncate at the 1st resample node (RN) bound of the ov-FOV. NOTE: resample pos is an interpolation point, does not exist in data, so we need a true data bound, i.e., the lowest point that's greater than the resample window that bounds the RN.
   2. Suc window-file 2: truncate at the 2nd RN bound of the ov-FOV
      
   
   
3. when resampling, we resample each window file.
   
4. window file should be larger than a processing window for polyfit.
5. when final concatenating, do beginning-alignment, discard overlap.
   
6. for unwrapping,  data needed: i_window_file; count_revolution;
7. for resampling, data needed: sample rate/period in angles, resample window-size