Frame-level diffs

frame-level-diffs.py

##
# Example cell showing transformation logic
##

# sample initial conditions for array with 3 verts, 2 time stamps, 3 dims
a = np.array([
  [ # vert
    [3,3,3], # vert 0 time 0
    [7,7,7] 
  ],
  [
    [9,9,9], # vert 0 time 1
    [11,11,11]   
  ],
  [
    [5,5,5], # vert 0 time 2
    [11,11,11]   
  ]
])

# time-stamp level offsets; shape = a.shape[0], a.shape[1]-1, a.shape[2]
b = np.diff(a, axis=1)

# to find the final positions, take starting positions + frame by frame offsets
initial = np.expand_dims( a[:,0,:], axis=1 )
sums = np.cumsum(b, axis=1)
cumsums = np.add(initial, sums)
frames = np.concatenate([initial, cumsums], axis=1)
np.all(frames == a)