From cdbf7acc80eb4c559f6259202138cbecc53fc3fb Mon Sep 17 00:00:00 2001
From: 0penBrain <48731257+0penBrain@users.noreply.github.com>
Date: Sun, 12 Sep 2021 19:45:28 +0200
Subject: [PATCH] [Core] Rotation : fix gimbal lock handling

 + fix Euler representation on GUI
---
 src/Base/Rotation.cpp |  4 ++--
 src/Gui/Placement.ui  | 18 +++++++++---------
 2 files changed, 11 insertions(+), 11 deletions(-)

diff --git a/src/Base/Rotation.cpp b/src/Base/Rotation.cpp
index ec15219388..118a7c6563 100644
--- a/src/Base/Rotation.cpp
+++ b/src/Base/Rotation.cpp
@@ -673,13 +673,13 @@ void Rotation::getYawPitchRoll(double& y, double& p, double& r) const
     double qd2 = 2.0*(q13-q02);
 
     // handle gimbal lock
-    if (fabs(qd2-1.0) < DBL_EPSILON) {
+    if (fabs(qd2-1.0) <= DBL_EPSILON) {
         // north pole
         y = 0.0;
         p = D_PI/2.0;
         r = 2.0 * atan2(quat[0],quat[3]);
     }
-    else if (fabs(qd2+1.0) < DBL_EPSILON) {
+    else if (fabs(qd2+1.0) <= DBL_EPSILON) {
         // south pole
         y = 0.0;
         p = -D_PI/2.0;
diff --git a/src/Gui/Placement.ui b/src/Gui/Placement.ui
index 844efe6d0a..a8fc09cedd 100644
--- a/src/Gui/Placement.ui
+++ b/src/Gui/Placement.ui
@@ -347,7 +347,7 @@
                </sizepolicy>
               </property>
               <property name="text">
-               <string>Around y-axis:</string>
+               <string>Pitch (around y-axis):</string>
               </property>
              </widget>
             </item>
@@ -360,7 +360,7 @@
                </sizepolicy>
               </property>
               <property name="text">
-               <string>Around z-axis:</string>
+               <string>Roll (around x-axis):</string>
               </property>
              </widget>
             </item>
@@ -373,28 +373,28 @@
                </sizepolicy>
               </property>
               <property name="text">
-               <string>Around x-axis:</string>
+               <string>Yaw (around z-axis):</string>
               </property>
              </widget>
             </item>
             <item row="0" column="1">
-             <widget class="Gui::QuantitySpinBox" name="rollAngle">
+             <widget class="Gui::QuantitySpinBox" name="yawAngle">
               <property name="toolTip">
-               <string>Rotation around the x-axis</string>
+               <string>Yaw (around z-axis)</string>
               </property>
              </widget>
             </item>
             <item row="1" column="1">
              <widget class="Gui::QuantitySpinBox" name="pitchAngle">
               <property name="toolTip">
-               <string>Rotation around the y-axis</string>
+               <string>Pitch (around y-axis)</string>
               </property>
              </widget>
             </item>
             <item row="2" column="1">
-             <widget class="Gui::QuantitySpinBox" name="yawAngle">
+             <widget class="Gui::QuantitySpinBox" name="rollAngle">
               <property name="toolTip">
-               <string>Rotation around the z-axis</string>
+               <string>Roll (around the x-axis)</string>
               </property>
              </widget>
             </item>
@@ -414,7 +414,7 @@
         </item>
         <item>
          <property name="text">
-          <string>Euler angles (xy'z'')</string>
+          <string>Euler angles (zy'x'')</string>
          </property>
         </item>
        </widget>