[dartpy] Add wrapper for convertToPositions() in class BallJoint

CHANGELOG.md

@@ -31,6 +31,13 @@
   * Added shadow technique: [#1348](https://github.com/dartsim/dart/pull/1348)
   * Added findSolution and solveAndApply to InverseKinematics: [#1358](https://github.com/dartsim/dart/pull/1358)
   * Added InteractiveFrame and ImGui APIs: [#1359](https://github.com/dartsim/dart/pull/1359)
+  * Added bindings for Joint::getTransformFrom{Parent|Child}BodyNode(): [#1377](https://github.com/dartsim/dart/pull/1377)
+  * Added bindings for BodyNode::getChild{BodyNode|Joint}(): [#1387](https://github.com/dartsim/dart/pull/1387)
+  * Added bindings for Inertia: [#1388](https://github.com/dartsim/dart/pull/1388)
+  * Added bindings for getting all BodyNodes from a Skeleton: [#1397](https://github.com/dartsim/dart/pull/1397)
+  * Added bindings for background color support in osg viewer: [#1398](https://github.com/dartsim/dart/pull/1398)
+  * Added bindings for BallJoint::convertToPositions(): [#1408](https://github.com/dartsim/dart/pull/1408)
+  * Fixed typos in Skeleton: [#1392](https://github.com/dartsim/dart/pull/1392)
 
 * Build
 

CONTRIBUTING.md

@@ -48,6 +48,7 @@ The code doesn't need to be perfect right away, feel free to post work-in-progre
  [pchorak](https://github.com/pchorak)              | bug fixes
  [acxz](https://github.com/acxz)                    | doxygen warning fix
  [Addisu Taddese](https://github.com/azeey)         | bug fix in ode collision detector
+ [Christoph Hinze](https://github.com/chhinze)      | python bindings
 
 You can find the complete contribution history in [here](https://github.com/dartsim/dart/graphs/contributors).
 

python/dartpy/dynamics/BallJoint.cpp

@@ -96,6 +96,12 @@ void BallJoint(py::module& m)
             return dart::dynamics::BallJoint::getStaticType();
           },
           ::py::return_value_policy::reference_internal)
+      .def_static(
+          "convertToPositions",
+          +[](const Eigen::Matrix3d& _tf) -> Eigen::Vector3d {
+            return dart::dynamics::BallJoint::convertToPositions(_tf);
+          },
+          ::py::arg("tf"))
       .def_static(
           "convertToTransform",
           +[](const Eigen::Vector3d& _positions) -> Eigen::Isometry3d {

python/tests/unit/dynamics/test_joint.py

@@ -121,5 +121,26 @@ def test_access_to_parent_child_transforms():
     assert np.allclose(childToJointTf.matrix(), storedChildTf.matrix())
 
 
+def test_BallJoint_positions_conversion():
+    assert np.allclose(
+        dart.dynamics.BallJoint.convertToPositions(np.eye(3)),
+        np.zeros((1, 3))
+    )
+    assert np.allclose(
+        dart.dynamics.BallJoint.convertToPositions(
+            np.array([[0, 1, 0], [-1, 0, 0], [0, 0, 1]])),
+        np.array([0, 0, -np.pi/2])
+    )
+
+    for i in range(30):
+        ballJointPos = np.random.uniform(-np.pi/2, np.pi/2, 3)
+        assert np.allclose(
+            dart.dynamics.BallJoint.convertToPositions(
+                dart.dynamics.BallJoint.convertToRotation(ballJointPos)
+            ),
+            ballJointPos
+        )
+
+
 if __name__ == "__main__":
     pytest.main()