Change quaternion convention to 'xyzw'

Signed-off-by: Addisu Z. Taddese <addisu@openrobotics.org>

specify_pose/proposal.md

@@ -59,7 +59,7 @@ This proposal suggests that the following modifications be made to the `//pose`
 <pose rotation_format="euler_rpy" degrees="true">{xyz}  {rpy_degrees}</pose>
 
 <!-- Not yet confirmed -->
-<pose rotation_format="quat_wxyz">{xyz}  {quat_wxyz}</pose>
+<pose rotation_format="quat_xyzw">{xyz}  {quat_xyzw}</pose>
 ```
 
 ## Motivation
@@ -147,7 +147,7 @@ go against the convention used for other elements (e.g.
 `//joint/axis/xyz`, `//inertia/ixx,...`).
 
 Additionally, allowing the rotation format to be represented implicitly by
-mutally exclusive attributes (e.g. `euler_rpy`, `quat_wxyz`) may
+mutally exclusive attributes (e.g. `euler_rpy`, `quat_xyzw`) may
 complicate parsing to an extent.
 
 *Use `//pose/rot` instead of `//pose/rotation`*
@@ -174,7 +174,7 @@ angle. This is the default for legacy purposes.
     * It is not suggested to use this for a text-storage format.
     * Same precision as suggested below for quaternions: Use 17 digits of
     precision, and consider separating each value on a new line.
-* `@rotation_format="quat_wxyz"` - Quaternion as a 4-tuple, represented as  `(w, x, y, z)`, where `w`
+* `@rotation_format="quat_xyzw"` - Quaternion as a 4-tuple, represented as  `(x, y, z, w)`, where `w`
 is the real component. This is the recommended format for machine-generated files (e.g. calibration artifacts).
     * It is encouraged to use 17 digits of precision when possible (C++'s
     default from `std::numeric_limits<double>::max_digits10`).
@@ -188,16 +188,16 @@ Examples:
 ```xml
 <pose degrees="true">{xyz}   90 45 180</pose>
 
-<pose rotation_format="quat_wxyz">
+<pose rotation_format="quat_xyzw">
     {xyz}
 
-    0.27059805007309851
     -0.27059805007309845
     0.65328148243818818
     0.65328148243818829
+    0.27059805007309851
 </pose>
 
-<pose rotation_format="quat_wxyz">{xyz}   0.27059805007309851 -0.27059805007309845 0.65328148243818818 0.65328148243818829</pose> <!-- Same as above, but on one line -->
+<pose rotation_format="quat_xyzw">{xyz}   -0.27059805007309845 0.65328148243818818 0.65328148243818829 0.27059805007309851</pose> <!-- Same as above, but on one line -->
 
 <pose rotation_format="euler_rpy" degrees="false"> <!-- This is not recommended. -->
     {xyz}
@@ -229,7 +229,8 @@ $ cat ./share/doc/drake/VERSION.TXT
 
     # quat_wxyz
     quat_wxyz = RollPitchYaw(rpy_radians).ToQuaternion().wxyz()
-    for x in quat_wxyz: print(f"{x:.17g}")
+    quat_xyzw = np.r_[quat_wxyz[1:], quat_wxyz[0]]
+    for x in quat_xyzw : print(f"{x:.17g}")
 -->
 
 **Alternatives Considered**
@@ -249,19 +250,19 @@ less verbose while still being concise (e.g. avoiding abbreviations).
 *Use `//pose/{rotation_format}` instead of
 `//pose/@rotation_format="rotation_format"]`*
 
-Specifying something like `//pose/euler_rpy` or `//pose/quat_wxyz` may
+Specifying something like `//pose/euler_rpy` or `//pose/quat_xyzw` may
 encounter some of the parsing complication for mutually exclusive tags, as
 mentioned above.
 
-*Use `@rotation_format="quaternion"` instead of `@rotation_format="quat_wxyz"`*
+*Use `@rotation_format="quaternion"` instead of `@rotation_format="quat_xyzw"`*
 
 In general, it can be confusing when interfacing different libraries that use
 different orderings for quaternions and those ordering are not readily stated
 in the API (or even the documentation). Instead, the author recommends
 explicitly enumerating this order in a relatively unambiguous way that is shown
 directly in the specification.
 
-*Add `@rotation_format="quat_xyzw`, `@rotation_format="euler_intrinsic_rpy"`, `@rotation_format="matrix"`,
+*Add `@rotation_format="quat_wxyz`, `@rotation_format="euler_intrinsic_rpy"`, `@rotation_format="matrix"`,
 `@rotation_format="axis_angle"`, `@rotation_format="axang3`, etc.*
 
 The author feels that too many representations and permutations may make it
@@ -313,24 +314,24 @@ representations (all printed up to 17 degrees of precision):
 <!-- No translation, identity orientation -->
 <pose rotation_format="euler_rpy" degrees="true">0 0 0   0 0 0</pose>
 <pose>0 0 0   0 0 0</pose>
-<pose rotation_format="quat_wxyz">0 0 0   1 0 0 0</pose>
+<pose rotation_format="quat_xyzw">0 0 0   0 0 0 1</pose>
 
 <!-- No translation, rotate 90 degrees about the x-axis -->
 <pose rotation_format="euler_rpy" degrees="true">0 0 0   90 0 0</pose>
 <pose>0 0 0   1.5707963267948966 0 0</pose>
 <pose rotation_format="euler_rpy" degrees="false">0 0 0  1.5707963267948966 0 0</pose>
-<pose rotation_format="quat_wxyz">
+<pose rotation_format="quat_xyzw">
     0 0 0
-    0.7071067811865475 0.7071067811865475 0 0
+    0.7071067811865475 0 0 0.7071067811865475
 </pose>
 
 <!-- No translation, a semi-arbitrary rotation -->
 <pose rotation_format="euler_rpy" degrees="true">0 0 0   10 20 30</pose>
 <pose>0 0 0   0.17453292519943295 0.3490658503988659 0.52359877559829882</pose>
-<pose rotation_format="quat_wxyz">
+<pose rotation_format="quat_xyzw">
     0 0 0
-    0.95154852464378847 0.038134576474850149 0.18930785741200001
-        0.23929833774473031
+    0.038134576474850149 0.18930785741200001
+        0.23929833774473031 0.95154852464378847
 </pose>
 ```
 
@@ -374,7 +375,7 @@ Some examples for `//body`, with default `//compiler` settings
 (`@angle="degree"`, `@eulerseq="xyz"`):
 
 ```xml
-<body pos="{xyz}" quat="{quat_wxyz}" .../>
+<body pos="{xyz}" quat="{quat_xyzw}" .../>
 <!-- or -->
 <body pos="{xyz}" euler="{rpy_degrees}" .../>
 ```