compat/euler: move gimbal lock from yaw to roll

Tested-by: Yuri Vostrenkov

1 files changed, 22 insertions, 37 deletions

diff --git a/compat/euler.cpp b/compat/euler.cpp
index 44b34f90..e9789bee 100644
--- a/compat/euler.cpp
+++ b/compat/euler.cpp
@@ -2,53 +2,38 @@
 #include "math-imports.hpp"
 #include <cmath>
 
+// rotation order is XYZ
+
 namespace euler {
 
 euler_t OTR_COMPAT_EXPORT rmat_to_euler(const rmat& R)
 {
-    const double cy = sqrt(R(2,2)*R(2, 2) + R(2, 1)*R(2, 1));
-    const bool large_enough = cy > 1e-10;
-    if (large_enough)
-       return {
-           atan2(-R(1, 0), R(0, 0)),
-           atan2(R(2, 0), cy),
-           atan2(-R(2, 1), R(2, 2))
-       };
-    else
-        return {
-           atan2(R(0, 1), R(1, 1)),
-           atan2(R(2, 0), cy),
-           0
-        };
+    double alpha, beta, gamma;
+
+    beta  = atan2( -R(2,0), sqrt(R(2,1)*R(2,1) + R(2,2)*R(2,2)) );
+    alpha = atan2( R(1,0), R(0,0));
+    gamma = atan2( R(2,1), R(2,2));
+
+    return { alpha, beta, gamma };
 }
 
-// tait-bryan angles, not euler
-rmat OTR_COMPAT_EXPORT euler_to_rmat(const euler_t& input)
+rmat OTR_COMPAT_EXPORT euler_to_rmat(const euler_t& e)
 {
-    const double H = -input(0);
-    const double P = -input(1);
-    const double B = -input(2);
+    const double X = -e(2);
+    const double Y = -e(1);
+    const double Z = -e(0);
 
-    const auto c1 = cos(H);
-    const auto s1 = sin(H);
-    const auto c2 = cos(P);
-    const auto s2 = sin(P);
-    const auto c3 = cos(B);
-    const auto s3 = sin(B);
+    const double cx = cos(X);
+    const double sx = sin(X);
+    const double cy = cos(Y);
+    const double sy = sin(Y);
+    const double cz = cos(Z);
+    const double sz = sin(Z);
 
     return {
-        // z
-        c1*c2,
-        c1*s2*s3 - c3*s1,
-        s1*s3 + c1*c3*s2,
-        // y
-        c2*s1,
-        c1*c3 + s1*s2*s3,
-        c3*s1*s2 - c1*s3,
-        // x
-        -s2,
-        c2*s3,
-        c2*c3
+        cy*cz,              -cy*sz,             sy,
+        cz*sx*sy + cx*sz,   cx*cz - sx*sy*sz,   -cy*sx,
+        -cx*cz*sy + sx*sz,  cz*sx + cx*sy*sz,   cx*cy,
     };
 }