example: fixing ellipsoid-joint python example

CHANGELOG.md

@@ -14,6 +14,9 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 - Add `DataTpl::lastChild` deprecation notice in Python binding
 - Fix `addFrame` to ignore frame without inertial to preserse parent body's CoM
 
+### Fixed
+- Fix `ellipsoid-joint-kinematics.py` example
+
 ## [4.1.0] - 2026-07-07
 
 ### Added

examples/ellipsoid-joint-kinematics.py

@@ -11,15 +11,7 @@
 
 import numpy as np
 import pinocchio as pin
-
-# For visualization (optional)
-try:
-    from pinocchio.visualize import MeshcatVisualizer
-
-    VISUALIZE = True
-except ImportError:
-    print("MeshcatVisualizer not available. Skipping visualization.")
-    VISUALIZE = False
+from pinocchio.visualize import MeshcatVisualizer
 
 
 def create_ellipsoid_robot(radius_x=0.5, radius_y=0.3, radius_z=0.2):
@@ -206,11 +198,8 @@ def compute_dynamics_example():
 
 def visualize_ellipsoid_motion():
     """Visualize the ellipsoid joint motion in MeshCat."""
-    if not VISUALIZE:
-        print("\nVisualization skipped (MeshcatVisualizer not available)")
-        return
 
-    if not hasattr(pin, "coal"):
+    if not pin.WITH_COLLISION:
         print("\nVisualization skipped (coal not available)")
         print("Install with: conda install -c conda-forge coal")
         print("Then recompile Pinocchio with -DBUILD_WITH_COLLISION_SUPPORT=ON")
@@ -225,109 +214,102 @@ def visualize_ellipsoid_motion():
     model = create_ellipsoid_robot(radius_x, radius_y, radius_z)
 
     # Add visual geometry
-    try:
-        geom_model = pin.GeometryModel()
-
-        # 1. Add the ELLIPSOID SURFACE as a visual object
-        ellipsoid_shape = pin.coal.Ellipsoid(radius_x, radius_y, radius_z)
-        ellipsoid_geom = pin.GeometryObject(
-            "ellipsoid_surface",
-            0,  # Universe frame
-            ellipsoid_shape,
-            pin.SE3.Identity(),
-        )
-        ellipsoid_geom.meshColor = np.array(
-            [0.8, 0.8, 0.8, 0.3]
-        )  # Semi-transparent gray
-        geom_model.addGeometryObject(ellipsoid_geom)
-
-        # 2. Add a small sphere to show the contact point on the ellipsoid
-        contact_sphere = pin.coal.Sphere(0.03)
-        contact_geom = pin.GeometryObject(
-            "contact_point",
-            model.getJointId("ellipsoid"),
-            contact_sphere,
-            pin.SE3.Identity(),  # At the joint frame (on the ellipsoid surface)
-        )
-        contact_geom.meshColor = np.array([1.0, 0.0, 0.0, 1.0])  # Red
-        geom_model.addGeometryObject(contact_geom)
-
-        # 3. Add a box to visualize the body orientation
-        box = pin.coal.Box(0.1, 0.1, 0.3)
-        box_geom = pin.GeometryObject(
-            "body_visual",
-            model.getJointId("ellipsoid"),
-            box,
-            pin.SE3(np.eye(3), np.array([0.0, 0.0, 0.15])),
-        )
-        box_geom.meshColor = np.array([0.2, 0.6, 1.0, 1.0])  # Blue
-        geom_model.addGeometryObject(box_geom)
+    geom_model = pin.GeometryModel()
+
+    # 1. Add the ELLIPSOID SURFACE as a visual object
+    ellipsoid_shape = pin.coal.Ellipsoid(radius_x, radius_y, radius_z)
+    ellipsoid_geom = pin.GeometryObject(
+        "ellipsoid_surface",
+        0,  # Universe frame
+        pin.SE3.Identity(),
+        ellipsoid_shape,
+    )
+    ellipsoid_geom.meshColor = np.array([0.8, 0.8, 0.8, 0.3])  # Semi-transparent gray
+    geom_model.addGeometryObject(ellipsoid_geom)
+
+    # 2. Add a small sphere to show the contact point on the ellipsoid
+    contact_sphere = pin.coal.Sphere(0.03)
+    contact_geom = pin.GeometryObject(
+        "contact_point",
+        model.getJointId("ellipsoid"),
+        pin.SE3.Identity(),  # At the joint frame (on the ellipsoid surface)
+        contact_sphere,
+    )
+    contact_geom.meshColor = np.array([1.0, 0.0, 0.0, 1.0])  # Red
+    geom_model.addGeometryObject(contact_geom)
+
+    # 3. Add a box to visualize the body orientation
+    box = pin.coal.Box(0.1, 0.1, 0.3)
+    box_geom = pin.GeometryObject(
+        "body_visual",
+        model.getJointId("ellipsoid"),
+        pin.SE3(np.eye(3), np.array([0.0, 0.0, 0.15])),
+        box,
+    )
+    box_geom.meshColor = np.array([0.2, 0.6, 1.0, 1.0])  # Blue
+    geom_model.addGeometryObject(box_geom)
 
-        # Initialize visualizer
+    # Initialize visualizer
+    try:
         viz = MeshcatVisualizer(model, geom_model, geom_model)
         viz.initViewer(open=True)
         viz.loadViewerModel()
-
-        print("\n✓ Visualization initialized!")
-        print("  - Gray ellipsoid: The constraint surface")
-        print("  - Red sphere: Contact point on the surface")
-        print("  - Blue box: The rigid body attached to the joint")
-        print("\nAnimating ellipsoid joint motion...")
-        print(
-            "Open http://127.0.0.1:7000/static/ in your browser to see the animation."
+    except ImportError as error:
+        print(error)
+        print("\nVisualization skipped (MeshcatVisualizer not available)")
+        return
+    print("\n✓ Visualization initialized!")
+    print("  - Gray ellipsoid: The constraint surface")
+    print("  - Red sphere: Contact point on the surface")
+    print("  - Blue box: The rigid body attached to the joint")
+    print("\nAnimating ellipsoid joint motion...")
+    print("Open http://127.0.0.1:7000/static/ in your browser to see the animation.")
+
+    # Animate through different configurations
+    import time
+
+    t = 0.0
+    dt = 0.02
+
+    for i in range(500):
+        # Create a smooth trajectory on the ellipsoid
+        q = np.array(
+            [
+                0.8 * np.sin(1.0 * t),
+                0.6 * np.sin(1.2 * t + 1.0),
+                0.4 * np.sin(0.8 * t + 0.5),
+            ]
         )
 
-        # Animate through different configurations
-        import time
-
-        t = 0.0
-        dt = 0.02
+        viz.display(q)
+        time.sleep(dt)
+        t += dt
 
-        for i in range(500):
-            # Create a smooth trajectory on the ellipsoid
-            q = np.array(
-                [
-                    0.8 * np.sin(1.0 * t),
-                    0.6 * np.sin(1.2 * t + 1.0),
-                    0.4 * np.sin(0.8 * t + 0.5),
-                ]
+        if i % 50 == 0:
+            print(
+                f"  Frame {i}/500 - Configuration: \n"
+                f"    [{q[0]:.3f}, {q[1]:.3f}, {q[2]:.3f}]"
             )
 
-            viz.display(q)
-            time.sleep(dt)
-            t += dt
-
-            if i % 50 == 0:
-                print(
-                    f"  Frame {i}/500 - Configuration: \n"
-                    f"    [{q[0]:.3f}, {q[1]:.3f}, {q[2]:.3f}]"
-                )
-
-        # create extra motion that slides along the principal axes q0
-        for angle in np.linspace(0, 2 * np.pi, 100):
-            q = np.array([0.5 * np.cos(angle), 0.0, 0.0])
-            viz.display(q)
-            time.sleep(dt)
-
-        # q1 axis
-        for angle in np.linspace(0, 2 * np.pi, 100):
-            q = np.array([0.0, 0.3 * np.cos(angle), 0.0])
-            viz.display(q)
-            time.sleep(dt)
-
-        # q2 axis
-        for angle in np.linspace(0, 2 * np.pi, 100):
-            q = np.array([0.0, 0.0, 3.14 * np.cos(angle)])
-            viz.display(q)
-            time.sleep(dt)
-
-        print("\n✓ Animation completed!")
-
-    except Exception as e:
-        print(f"\nVisualization error: {e}")
-        import traceback
-
-        traceback.print_exc()
+    # create extra motion that slides along the principal axes q0
+    for angle in np.linspace(0, 2 * np.pi, 100):
+        q = np.array([0.5 * np.cos(angle), 0.0, 0.0])
+        viz.display(q)
+        time.sleep(dt)
+
+    # q1 axis
+    for angle in np.linspace(0, 2 * np.pi, 100):
+        q = np.array([0.0, 0.3 * np.cos(angle), 0.0])
+        viz.display(q)
+        time.sleep(dt)
+
+    # q2 axis
+    for angle in np.linspace(0, 2 * np.pi, 100):
+        q = np.array([0.0, 0.0, 3.14 * np.cos(angle)])
+        viz.display(q)
+        time.sleep(dt)
+
+    print("\n✓ Animation completed!")
 
 
 def main():