Add example to visualize floating base velocity

CHANGELOG.md

@@ -12,6 +12,9 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
 ### Fixed
 - Remove a lot of warnings ([#2139](https://github.com/stack-of-tasks/pinocchio/pull/2139))
 
+### Added
+- Add `examples/floating-base-velocity-viewer.py` to visualize floating base velocity [#2143](https://github.com/stack-of-tasks/pinocchio/pull/2143)
+
 ## [2.7.0] - 2024-01-23
 
 ### Added

examples/floating-base-velocity-viewer.py

@@ -0,0 +1,84 @@
+import pinocchio as pin
+import numpy as np
+import hppfcl
+
+from pinocchio.visualize import MeshcatVisualizer
+from time import sleep
+
+
+def create_pin_cube_model(j0="freeflyer"):
+    model = pin.Model()
+
+    if j0 == "freeflyer":
+        j0 = pin.JointModelFreeFlyer()
+    elif j0 == "spherical":
+        j0 = pin.JointModelSpherical()
+    elif j0 == "sphericalzyx":
+        j0 = pin.JointModelSphericalZYX()
+    else:
+        raise ValueError("Unknown joint type")
+
+    jointCube = model.addJoint(0, j0, pin.SE3.Identity(), "joint0")
+    M = pin.SE3.Identity()
+    model.appendBodyToJoint(jointCube, pin.Inertia.FromBox(1, 0.8, 0.4, 0.2), M)
+    return model
+
+
+def create_pin_geometry_cube_model(model):
+    jointCube = model.getFrameId("joint0")
+    geom_model = pin.GeometryModel()
+    cube_shape = hppfcl.Box(0.8, 0.4, 0.2)  # x, y, z
+    cube = pin.GeometryObject(
+        "cube_shape", 0, jointCube, cube_shape, pin.SE3.Identity()
+    )
+    cube.meshColor = np.array([1.0, 0.1, 0.1, 0.5])
+    geom_model.addGeometryObject(cube)
+    return geom_model
+
+
+def create_model(joint0_type="freeflyer"):
+    model = create_pin_cube_model(joint0_type)
+    geom_model = create_pin_geometry_cube_model(model)
+    return model, geom_model
+
+
+def pin_step(model, vizer, v_index_increment, dt=0.1):
+    q = pin.neutral(model)
+    v = np.zeros(model.nv)
+    v[v_index_increment] += 1.0
+
+    vizer.display(q)
+    print(f"{q=}, {v=}")
+
+    sleep(1)
+
+    q_next = pin.integrate(model, q, v * dt)
+
+    print(f"{q_next=}")
+    return q_next
+
+
+if __name__ == "__main__":
+    list_joint0 = ["freeflyer", "sphericalzyx", "spherical"]
+
+    for joint0_name in list_joint0:
+        print(f"\njoint0_name = {joint0_name}")
+
+        model, geom_model = create_model(joint0_name)
+        print(f"{model.nq=}")
+        print(f"{model.nv=}")
+
+        q = pin.neutral(model)
+        print(f"neutral q configuration: {q=}")
+
+        vizer = MeshcatVisualizer(model, geom_model, geom_model)
+        vizer.initViewer(open=True, loadModel=True)
+        vizer.display(q)
+
+        sleep(2)
+
+        for i in range(model.nv):
+            print(f"v[{i}] += 1")
+            q_next = pin_step(model, vizer, i, dt=0.2)
+            vizer.display(q_next)
+            sleep(2)