add 2 examples in states

examples/states/README.rst

@@ -15,10 +15,8 @@ States can also be given to dynamical models (which predicts the next state give
 Here are few examples that you can find in this folder:
 
 1. ``basics.py``: demonstrate the various features of the ``State`` class.
-2. ``robot.py``: get the joint states of a specific robot and print them.
-3. ``world.py``: get the pose state of an object loaded in the world.
-4. ``sensor.py``: get the state of a sensor.
-5. ``interface.py``: get the state from a game controller interface.
+2. ``world.py``: get the pose state of an object loaded in the world.
+3. ``robot.py``: get the joint states of a specific robot and print them.
 
 
 Simple Example

examples/states/robot.py

@@ -0,0 +1,34 @@
+#!/usr/bin/env python
+"""Get the robot's joint position and velocity states.
+
+In this example, we load a Kuka manipulator and print the joint position and velocity states. You can try to move the
+robot and see how it affects the states.
+"""
+
+from itertools import count
+import pyrobolearn as prl
+
+
+# Create simulator
+sim = prl.simulators.Bullet()
+
+# create world
+world = prl.worlds.BasicWorld(sim)
+
+# load the kuka robot
+robot = world.load_robot('kuka_iiwa')
+
+# create joint states
+state = prl.states.JointPositionState(robot, joint_ids=[1, 2]) + prl.states.JointVelocityState(robot, joint_ids=1)
+
+# perform simulation
+for t in count():
+
+    # update the state
+    state()  # or state.read()
+
+    # print the state
+    print(state)
+
+    # step in simulation
+    world.step(sleep_dt=sim.dt)

examples/states/world.py

@@ -0,0 +1,34 @@
+#!/usr/bin/env python
+"""Get the cartesian position state of an object loaded in the world.
+
+In this example, we load a sphere in the world which can be moved using the mouse. At every time step, we print the
+cartesian position state of the sphere.
+"""
+
+from itertools import count
+import pyrobolearn as prl
+
+
+# Create simulator
+sim = prl.simulators.Bullet()
+
+# create world
+world = prl.worlds.BasicWorld(sim)
+
+# load a sphere in the world
+sphere = world.load_sphere(position=(0., 0., 1.), mass=1., radius=0.2, color=(0.8, 0, 0, 1.), return_body=True)
+
+# create state
+state = prl.states.PositionState(sphere)
+
+# perform simulation
+for t in count():
+
+    # update the state
+    state()  # or state.read()
+
+    # print the state
+    print(state)
+
+    # step in simulation
+    world.step(sleep_dt=sim.dt)