Fix ZYX order for BVH format

app_new.py

@@ -233,21 +233,21 @@ def _quat_from_two_vectors(v1, v2):
     q = np.array([w, cross[0], cross[1], cross[2]])
     return q / (np.linalg.norm(q) + 1e-10)
 
-def _quat_to_euler(q):
-    """Quaternion to Euler XYZ (degrees)."""
+def _quat_to_euler_zyx(q):
+    """Quaternion to Euler ZYX order (degrees) - standard BVH format."""
     w, x, y, z = q
-    # Roll (X)
-    sinr = 2 * (w * x + y * z)
-    cosr = 1 - 2 * (x * x + y * y)
-    rx = np.arctan2(sinr, cosr)
-    # Pitch (Y)
-    sinp = 2 * (w * y - z * x)
-    ry = np.arcsin(np.clip(sinp, -1, 1))
-    # Yaw (Z)
+    # Z rotation (yaw)
     siny = 2 * (w * z + x * y)
     cosy = 1 - 2 * (y * y + z * z)
     rz = np.arctan2(siny, cosy)
-    return np.degrees([rx, ry, rz])
+    # Y rotation (pitch)
+    sinp = 2 * (w * y - z * x)
+    ry = np.arcsin(np.clip(sinp, -1, 1))
+    # X rotation (roll)
+    sinr = 2 * (w * x + y * z)
+    cosr = 1 - 2 * (x * x + y * y)
+    rx = np.arctan2(sinr, cosr)
+    return np.degrees([rz, ry, rx])  # ZYX order for BVH
 
 def joints_to_bvh(joints, output_path, fps=20):
     """Convert joint positions to BVH with proper local rotations."""
@@ -298,9 +298,9 @@ def joints_to_bvh(joints, output_path, fps=20):
                 local_rot = global_rot
 
             global_quats[j] = global_rot
-            all_rotations[frame, j] = _quat_to_euler(local_rot)
+            all_rotations[frame, j] = _quat_to_euler_zyx(local_rot)
 
-    # Write BVH
+    # Write BVH (ZYX rotation order - standard for BVH)
     with open(output_path, "w") as f:
         f.write("HIERARCHY\n")
         def write_joint(idx, indent):
@@ -308,7 +308,7 @@ def joints_to_bvh(joints, output_path, fps=20):
             pre = "  " * indent
             f.write(f"{'ROOT' if idx==0 else pre+'JOINT'} {name}\n{pre}{{\n")
             f.write(f"{pre}  OFFSET {off[0]:.6f} {off[1]:.6f} {off[2]:.6f}\n")
-            f.write(f"{pre}  CHANNELS {'6 Xposition Yposition Zposition ' if idx==0 else '3 '}Xrotation Yrotation Zrotation\n")
+            f.write(f"{pre}  CHANNELS {'6 Xposition Yposition Zposition ' if idx==0 else '3 '}Zrotation Yrotation Xrotation\n")
             if children[idx]:
                 for c in children[idx]: write_joint(c, indent + 1)
             else: