update comments at top of module doco

Author: petercorke

docs/source/func_3d.rst

@@ -1,6 +1,7 @@
 Transforms in 3D
 ================
 
+
 .. automodule:: spatialmath.base.transforms3d
    :members:
    :undoc-members:

spatialmath/base/quaternions.py

@@ -2,6 +2,12 @@
 # Copyright (c) 2000 Peter Corke
 # MIT Licence, see details in top-level file: LICENCE
 
+"""
+These functions create and manipulate quaternions or unit quaternions.
+The quaternion is represented
+by a 1D NumPy array with 4 elements: s, x, y, z.
+
+"""
 # pylint: disable=invalid-name
 
 import sys

spatialmath/base/transforms2d.py

@@ -3,8 +3,9 @@
 # MIT Licence, see details in top-level file: LICENCE
 
 """
-This modules contains functions to create and transform SO(2) and SE(2) matrices,
-respectively 2D rotation matrices and homogeneous tranformation matrices.
+These functions create and manipulate 2D rotation matrices and rigid-body
+transformations as 2x2 SO(2) matrices and 3x3 SE(2) matrices respectively.
+These matrices are represented as 2D NumPy arrays.
 
 Vector arguments are what numpy refers to as ``array_like`` and can be a list,
 tuple, numpy array, numpy row vector or numpy column vector.

spatialmath/base/transforms3d.py

@@ -3,8 +3,9 @@
 # MIT Licence, see details in top-level file: LICENCE
 
 """
-This modules contains functions to create and transform SO(3) and SE(3) matrices,
-respectively 3D rotation matrices and homogeneous tranformation matrices.
+These functions create and manipulate 3D rotation matrices and rigid-body
+transformations as 3x3 SO(3) matrices and 4x4 SE(3) matrices respectively.
+These matrices are represented as 2D NumPy arrays.
 
 Vector arguments are what numpy refers to as ``array_like`` and can be a list,
 tuple, numpy array, numpy row vector or numpy column vector.