Find the displacement vector of all particles between two frames.
Parameters:
t : DataFrame
trajectories
pos_columns = list
names of column with position [‘x’, ‘y’]
frame1 : integer
frame2 : integer
Returns:
DataFrame
indexed by particle, containing:
x, y, etc. (corresponding to frame1)
x_b, y_b, etc. (corresponding to frame2)
dx, dy, etc.
dr
direction (only if pos_columns=[‘x’, ‘y’])