nc = input_shape[2]
s = 1.5
t = 2.5
trans = np.array([[1, 0, 0, -t * ns], [0, 1, 0, -t * nr], [0, 0, 1, -t * nc],
[0, 0, 0, 1]])
trans_inv = np.linalg.inv(trans)
scale = np.array([[1 * s, 0, 0, 0], [0, 1 * s, 0, 0], [0, 0, 1 * s, 0],
[0, 0, 0, 1]])
gt_affine = trans_inv.dot(scale.dot(trans))
# create two random displacement fields
input_grid2world = gt_affine
target_grid2world = gt_affine
disp1, _ = vfu.create_random_displacement_3d(
np.array(input_shape, dtype=np.int32), input_grid2world,
np.array(tgt_sh, dtype=np.int32), target_grid2world)
disp1 = np.array(disp1, dtype=floating)
disp2, _ = vfu.create_random_displacement_3d(
np.array(input_shape, dtype=np.int32), input_grid2world,
np.array(tgt_sh, dtype=np.int32), target_grid2world)
disp2 = np.array(disp2, dtype=floating)
# compose the displacement fields
target_world2grid = np.linalg.inv(target_grid2world)
premult_index = target_world2grid.dot(input_grid2world)
premult_disp = target_world2grid
time_scaling = 1.0