Specify units of output motion field

pysteps/motion/darts.py

@@ -64,7 +64,8 @@ def DARTS(R, **kwargs):
     -------
     out : ndarray
         Three-dimensional array (2,m,n) containing the dense x- and y-components
-        of the motion field.
+        of the motion field in units of pixels / timestep as given by the input
+        array R.
 
     """
 

pysteps/motion/lucaskanade.py

@@ -172,7 +172,8 @@ def dense_lucaskanade(R, **kwargs):
     -------
     out : ndarray_
         If dense=True (the default), it returns the three-dimensional array (2,m,n)
-        containing the dense x- and y-components of the motion field.
+        containing the dense x- and y-components of the motion field in units of
+        pixels / timestep as given by the input array R.
         If dense=False, it returns a tuple containing the one-dimensional arrays
         x, y, u, v, where x, y define the vector locations, u, v define the x
         and y direction components of the vectors.

pysteps/motion/vet.py

@@ -431,7 +431,8 @@ def vet(input_images,
         Displacement Field (2D array representing the transformation) that
         warps the template image into the input image.
         The dimensions are (2,ni,nj), where the first
-        dimension indicates the displacement along x (0) or y (1).
+        dimension indicates the displacement along x (0) or y (1) in units of
+        pixels / timestep as given by the input_images array.
 
     intermediate_steps : list of ndarray_
         List with the first guesses obtained during the scaling procedure.