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Update example 11 notes
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‎examples/example_11/CMakeLists.txt‎

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@@ -8,7 +8,7 @@ ADD_EXECUTABLE(${EXECUTABLE} ${SOURCE})
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TARGET_LINK_LIBRARIES(${EXECUTABLE} PRIVATE bitrllib pthread boost_log)
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IF(ENABLE_CHRONO)
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TARGET_LINK_LIBRARIES(${EXECUTABLE} PRIVATE Chrono::Chrono_core)
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TARGET_LINK_LIBRARIES(${EXECUTABLE} PRIVATE Chrono::Chrono_core Chrono::Chrono_irrlicht)
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ENDIF ()
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IF(BITRL_WEBOTS)

‎examples/example_11/box_1.png‎

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‎examples/example_11/example_11.cpp‎

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*
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*/
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#include "bitrl/bitrl_config.h"
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#ifdef BITRL_CHRONO
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#include "bitrl/bitrl_types.h"
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#ifdef BITRL_LOG
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#define BOOST_LOG_DYN_LINK
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#include <boost/log/trivial.hpp>
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#endif
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#include <chrono/physics/ChSystemSMC.h>
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#include <chrono/physics/ChBodyEasy.h>
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#include <chrono_irrlicht/ChVisualSystemIrrlicht.h>
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#include "bitrl/utils/geometry/geom_point.h"
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#include "bitrl/utils/trajectory/line_segment_link.h"
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#include "bitrl/utils/trajectory/waypoint.h"
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namespace example_11
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{
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using bitrl::Null;
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using bitrl::real_t;
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using bitrl::uint_t;
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using bitrl::utils::geom::GeomPoint;
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using bitrl::utils::trajectory::LineSegmentLink;
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using bitrl::utils::trajectory::WayPoint;
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using bitrl::utils::trajectory::WaypointTrajectory;
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using namespace bitrl;
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using namespace chrono::irrlicht;
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// constants we will be using further below
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const uint_t WINDOW_HEIGHT = 800;
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const uint_t WINDOW_WIDTH = 1024;
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const real_t DT = 0.0001;
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const real_t SIM_TIME = 5.0;
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const std::string WINDOW_TITLE( "Example 11");
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struct LineSegmentData
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void prepare_visualization(chrono::irrlicht::ChVisualSystemIrrlicht& visual)
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{
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visual.SetWindowSize(WINDOW_WIDTH, WINDOW_WIDTH); //WINDOW_HEIGHT);
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visual.SetWindowTitle(WINDOW_TITLE);
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visual.Initialize();
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visual.AddLogo();
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visual.AddSkyBox();
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visual.AddCamera({0, -2, 1}, {0, 0, 0});
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visual.AddTypicalLights();
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visual.BindAll();
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}
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std::shared_ptr<chrono::ChBody> create_box(real_t xlength, real_t ylength, real_t zlength,
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real_t density, bool create_visualization)
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{
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/// \brief The maximum velocity
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/// allowed on the edge
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real_t Vmax{0.0};
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/// \brief The orientation of the
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/// segment with respect to the global coordinate
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/// frame. This may also dictate the orientation
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/// that a reference vehicle may have on the segment
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real_t theta{0.0};
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// build the chassis of the robot
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auto box = chrono_types::make_shared<chrono::ChBodyEasyBox>(xlength, ylength, zlength,
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density, create_visualization);
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box -> SetMass(1.0);
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box -> SetPos(chrono::ChVector3d(0.0, 0.0, 0.22));
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// allow the chassis to move
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box -> SetFixed(true);
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return box;
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}
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/// \brief The angular velocity on the segment
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real_t w{0.0};
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/// \brief The linear velocity on the segement
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real_t v{0.0};
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};
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typedef LineSegmentLink<2, Null, LineSegmentData> link_type;
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typedef link_type::w_point_type w_point_type;
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} // namespace example_11
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/*
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int main()
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{
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using namespace example_11;
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chrono::ChSystemSMC sys;
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// create a trajector of 4 links
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// the waypoints carry not data
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// but the the links
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// carry objects of type LineSegmentData
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WaypointTrajectory<link_type> trajectory(3);
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// build the body and add it to the system
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// we want to simulate
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auto box = create_box(1.0, 1.0, 1.0, 1.0, true);
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sys.Add(box);
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// start adding the links
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// that form the trajectory
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w_point_type p0(GeomPoint<2>({0.0, 0.0}), static_cast<uint_t>(0));
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w_point_type p1(GeomPoint<2>({1.0, 0.0}), static_cast<uint_t>(1));
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LineSegmentData data{1.0, 0.0, 0.0, 0.95};
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// create the object that handles the visualization
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chrono::irrlicht::ChVisualSystemIrrlicht visual;
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prepare_visualization(visual);
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visual.AttachSystem(&sys);
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link_type l0(p0, p1, static_cast<uint_t>(0), data);
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w_point_type p2(GeomPoint<2>({1.0, 0.0}), static_cast<uint_t>(2));
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w_point_type p3(GeomPoint<2>({2.0, 2.0}), static_cast<uint_t>(3));
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data.theta = bitrl::utils::unit_converter::degrees_to_rad(45.0);
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link_type l1(p2, p3, static_cast<uint_t>(1), data);
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while (visual.Run())
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{
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w_point_type p4(GeomPoint<2>({2.0, 2.0}), static_cast<uint_t>(4));
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w_point_type p5(GeomPoint<2>({2.0, 3.0}), static_cast<uint_t>(5));
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data.theta = bitrl::utils::unit_converter::degrees_to_rad(90.0);
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link_type l2(p2, p3, static_cast<uint_t>(2), data);
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// Irrlicht must prepare frame to draw
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visual.BeginScene();
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trajectory[0] = l0;
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trajectory[1] = l1;
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trajectory[2] = l2;
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// .. draw items belonging to Irrlicht scene, if any
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visual.Render();
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std::cout << "Trajectory number of links: " << trajectory.size() << std::endl;
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// .. draw a grid
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tools::drawGrid(&visual, 0.5, 0.5);
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for (const auto &link : trajectory)
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{
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std::cout << link.get_id() << std::endl;
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// Irrlicht must finish drawing the frame
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visual.EndScene();
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}
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return 0;
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}*/
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int main()
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{
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using namespace example_11;
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chrono::ChSystemSMC sys;
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// build the body and add it to the system
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// we want to simulate
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auto box = create_box(1.0, 1.0, 1.0, 1.0, true);
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sys.Add(box);
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auto position = box -> GetPos();
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BOOST_LOG_TRIVIAL(info)<<"Position of CoM: "<<position;
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BOOST_LOG_TRIVIAL(info)<<"Linear velocity of CoM: "<<box -> GetLinVel();
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auto pos_local = box->TransformPointParentToLocal(position);
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BOOST_LOG_TRIVIAL(info)<<"local position of CoM: "<<pos_local;
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}
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#else
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#include <iostream>
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int main()
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{
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std::cerr<<"You need PROJECTCHRONO configured with "
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<<"bitrl in order to run this example "
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<<"Reconfigure bitrl and set ENABLE_CHRONO=ON"<<std::endl;
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return 1;
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}
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#endif

‎examples/example_11/example_11.md‎

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\page bitrl_example_11 BitRL Example 11 Create a rigid body in Chrono
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The <a href="https://github.com/projectchrono/chrono">Chrono</a> library is the main library that _bitrl_ is using in order
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to simulate robots and create environments for reinforcement learning agents. As such, knowing your way around
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Chrono is essential. However, Chrono is a relatively large library with many components and therefore not necessarily easy
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to grasp. In a series of examples, we will see main components of the library that _bitrl_ utilizes.
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You should have compiled Chrono with <a href="https://irrlicht.sourceforge.io/">Irrlicht</a> support.
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The main interface for creating rigid bodies in Chrono is the <a href="https://api.projectchrono.org/9.0.0/classchrono_1_1_ch_body.html">ChBody</a>
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class. You can also find this <a href="https://api.projectchrono.org/9.0.0/rigid_bodies.html"> Rigid Bodies</a> helpful.
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_ChBody_ is an abstract class, and therefore we cannot instantiate it directly. Chrono provides various classes however we can
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immediately use. The one we will use in this example is the _ChBodyEasyBox_ class. This is defined in the _<chrono/physics/ChBodyEasy.h>_ header.
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Let's first create a box and try to visualize it. Below is the function that constructs a box.
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@code{.cpp}
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std::shared_ptr<chrono::ChBody> create_box(real_t xlength, real_t ylength, real_t zlength,
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real_t density, bool create_visualization)
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{
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// build the chassis of the robot
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auto box = chrono_types::make_shared<chrono::ChBodyEasyBox>(xlength, ylength, zlength,
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density, create_visualization);
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box -> SetMass(1.0);
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box -> SetPos(chrono::ChVector3d(0.0, 0.0, 0.22));
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// allow the chassis to move
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box -> SetFixed(true);
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return box;
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}
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@endcode
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The following is a helper for setting up the visualization
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@code{.cpp}
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void prepare_visualization(chrono::irrlicht::ChVisualSystemIrrlicht& visual)
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{
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visual.SetWindowSize(WINDOW_WIDTH, WINDOW_WIDTH); //WINDOW_HEIGHT);
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visual.SetWindowTitle(WINDOW_TITLE);
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visual.Initialize();
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visual.AddLogo();
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visual.AddSkyBox();
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visual.AddCamera({0, -2, 1}, {0, 0, 0});
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visual.AddTypicalLights();
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visual.BindAll();
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}
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@endcode
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Below is the main function:
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@code{.cpp}
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int main()
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{
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using namespace example_11;
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chrono::ChSystemSMC sys;
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// build the body and add it to the system
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// we want to simulate
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auto box = create_box(1.0, 1.0, 1.0, 1.0, true);
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sys.Add(box);
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// create the object that handles the visualization
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chrono::irrlicht::ChVisualSystemIrrlicht visual;
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prepare_visualization(visual);
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visual.AttachSystem(&sys);
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while (visual.Run())
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{
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// Irrlicht must prepare frame to draw
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visual.BeginScene();
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// .. draw items belonging to Irrlicht scene, if any
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visual.Render();
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// .. draw a grid
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tools::drawGrid(&visual, 0.5, 0.5);
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// Irrlicht must finish drawing the frame
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visual.EndScene();
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}
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}
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@endcode
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Compiling and running the code will not do anything exciting as can be verified by the image below
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<img src="./box_1.png" width="600" height="337"/>
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Rigid bodies in Chrono have a lot of attributes and the API is quite rich. Here are some of the method that we are typically interested
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@code{.cpp}
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// position of the CoM
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GetPos()
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// linear velocity of the CoM
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GetLinVel()
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// linear acceleration of the CoM
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GetLinAcc()
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@endcode
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Let's change the main function so that it prints the position and the velocity of the box:
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@code{.cpp}
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int main()
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{
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using namespace example_11;
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chrono::ChSystemSMC sys;
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// build the body and add it to the system
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// we want to simulate
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auto box = create_box(1.0, 1.0, 1.0, 1.0, true);
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sys.Add(box);
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BOOST_LOG_TRIVIAL(info)<<"Position of CoM: "<<box -> GetPos();
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BOOST_LOG_TRIVIAL(info)<<"Linear velocity of CoM: "<<box -> GetLinVel();
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}
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@endcode
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This prints the following
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@code
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[2026-02-07 11:40:39.051115] [0x00007fdfbd563800] [info] Position of CoM: 0 0 0.22
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[2026-02-07 11:40:39.051130] [0x00007fdfbd563800] [info] Linear velocity of CoM: 0 0 0
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@endcode
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A question to ask is to which coordinate system the output refers to, The world reference frame or the one local to the body?

‎examples/example_14/example_14.md‎

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\page bitrl_example_14 Example 14 Create an environment using Chrono
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\page bitrl_example_14 BitRL Example 14 Create an RL environment using Chrono
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In this example we will create an environment for reinforcement learning based
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on the <a href="https://github.com/projectchrono/chrono">Chrono</a> library.
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Specifically, we will create an environment that includes a <a href="https://en.wikipedia.org/wiki/Differential_wheeled_robot">differential drive system</a>.
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Note that the model we will create will not be of high fidelity as the purpose of the example is show how
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to use Chrono to create reinforcement learning environments.
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In order to be able to run this example you need to configure bitrl with Chrono support. You will also
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In order to be able to run this example you need to configure _bitrl_ with Chrono support. You will also
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need the <a href="https://irrlicht.sourceforge.io/">Irrlicht</a> library for visualising the robot.
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The following image shows an image of the environment we will create
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| ![Environment overview](./env.png) |
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|:------------------------------------:|
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## Create the robot
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<img src="./env.png" width="600" height="337"/>
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Below is the class that handles the robot model.
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