VehicleAckermann.cpp

Go to the documentation of this file.

/*+-------------------------------------------------------------------------+
  |                       MultiVehicle simulator (libmvsim)                 |
  |                                                                         |
  | Copyright (C) 2014-2023  Jose Luis Blanco Claraco                       |
  | Copyright (C) 2017  Borys Tymchenko (Odessa Polytechnic University)     |
  | Distributed under 3-clause BSD License                                  |
  |   See COPYING                                                           |
  +-------------------------------------------------------------------------+ */

#include <mrpt/opengl/COpenGLScene.h>
#include <mvsim/VehicleDynamics/VehicleAckermann.h>
#include <mvsim/World.h>

#include <cmath>
#include <rapidxml.hpp>

#include "xml_utils.h"

using namespace mvsim;
using namespace std;

// Ctor:
DynamicsAckermann::DynamicsAckermann(World* parent)
        : VehicleBase(parent, 4 /*num wheels*/)
{
        chassis_mass_ = 500.0;
        chassis_z_min_ = 0.20;
        chassis_z_max_ = 1.40;
        chassis_color_ = mrpt::img::TColor(0xe8, 0x30, 0x00);

        // Default shape:
        chassis_poly_.clear();
        chassis_poly_.emplace_back(-0.8, -1.0);
        chassis_poly_.emplace_back(-0.8, 1.0);
        chassis_poly_.emplace_back(1.5, 0.9);
        chassis_poly_.emplace_back(1.8, 0.8);
        chassis_poly_.emplace_back(1.8, -0.8);
        chassis_poly_.emplace_back(1.5, -0.9);
        updateMaxRadiusFromPoly();

        fixture_chassis_ = nullptr;
        for (int i = 0; i < 4; i++) fixture_wheels_[i] = nullptr;

        // Default values:
        // rear-left:
        wheels_info_[WHEEL_RL].x = 0;
        wheels_info_[WHEEL_RL].y = 0.9;
        // rear-right:
        wheels_info_[WHEEL_RR].x = 0;
        wheels_info_[WHEEL_RR].y = -0.9;
        // Front-left:
        wheels_info_[WHEEL_FL].x = 1.3;
        wheels_info_[WHEEL_FL].y = 0.9;
        // Front-right:
        wheels_info_[WHEEL_FR].x = 1.3;
        wheels_info_[WHEEL_FR].y = -0.9;
}

void DynamicsAckermann::dynamics_load_params_from_xml(
        const rapidxml::xml_node<char>* xml_node)
{
        const std::map<std::string, std::string> varValues = {{"NAME", name_}};

        // <chassis ...> </chassis>
        if (const rapidxml::xml_node<char>* xml_chassis =
                        xml_node->first_node("chassis");
                xml_chassis)
        {
                // Attribs:
                TParameterDefinitions attribs;
                attribs["mass"] = TParamEntry("%lf", &this->chassis_mass_);
                attribs["zmin"] = TParamEntry("%lf", &this->chassis_z_min_);
                attribs["zmax"] = TParamEntry("%lf", &this->chassis_z_max_);
                attribs["color"] = TParamEntry("%color", &this->chassis_color_);

                parse_xmlnode_attribs(
                        *xml_chassis, attribs, {},
                        "[DynamicsAckermann::dynamics_load_params_from_xml]");

                // Shape node (optional, fallback to default shape if none found)
                if (const rapidxml::xml_node<char>* xml_shape =
                                xml_chassis->first_node("shape");
                        xml_shape)
                        mvsim::parse_xmlnode_shape(
                                *xml_shape, chassis_poly_,
                                "[DynamicsAckermann::dynamics_load_params_from_xml]");
        }

        //<rl_wheel pos="0  1" mass="6.0" width="0.30" diameter="0.62" />
        //<rr_wheel pos="0 -1" mass="6.0" width="0.30" diameter="0.62" />
        //<fl_wheel mass="6.0" width="0.30" diameter="0.62" />
        //<fr_wheel mass="6.0" width="0.30" diameter="0.62" />
        const char* w_names[4] = {
                "rl_wheel",      // 0
                "rr_wheel",      // 1
                "fl_wheel",      // 2
                "fr_wheel"      // 3
        };
        // Load common params:
        for (size_t i = 0; i < 4; i++)
        {
                if (auto xml_wheel = xml_node->first_node(w_names[i]); xml_wheel)
                {
                        wheels_info_[i].loadFromXML(xml_wheel);
                }
                else
                {
                        world_->logFmt(
                                mrpt::system::LVL_WARN,
                                "No XML entry '%s' found: using defaults for wheel #%u",
                                w_names[i], static_cast<unsigned int>(i));
                }
        }

        //<f_wheels_x>1.3</f_wheels_x>
        //<f_wheels_d>2.0</f_wheels_d>
        // Load front ackermann wheels and other params:
        {
                double front_x = 1.3;
                double front_d = 2.0;
                TParameterDefinitions ack_ps;
                // Front wheels:
                ack_ps["f_wheels_x"] = TParamEntry("%lf", &front_x);
                ack_ps["f_wheels_d"] = TParamEntry("%lf", &front_d);
                // other params:
                ack_ps["max_steer_ang_deg"] = TParamEntry("%lf_deg", &max_steer_ang_);

                parse_xmlnode_children_as_param(
                        *xml_node, ack_ps, varValues,
                        "[DynamicsAckermann::dynamics_load_params_from_xml]");

                // Front-left:
                wheels_info_[WHEEL_FL].x = front_x;
                wheels_info_[WHEEL_FL].y = 0.5 * front_d;
                // Front-right:
                wheels_info_[WHEEL_FR].x = front_x;
                wheels_info_[WHEEL_FR].y = -0.5 * front_d;
        }

        // Vehicle controller:
        // -------------------------------------------------
        {
                const rapidxml::xml_node<char>* xml_control =
                        xml_node->first_node("controller");
                if (xml_control)
                {
                        rapidxml::xml_attribute<char>* control_class =
                                xml_control->first_attribute("class");
                        if (!control_class || !control_class->value())
                                throw runtime_error(
                                        "[DynamicsAckermann] Missing 'class' attribute in "
                                        "<controller> XML node");

                        const std::string sCtrlClass = std::string(control_class->value());
                        if (sCtrlClass == ControllerRawForces::class_name())
                                controller_ = std::make_shared<ControllerRawForces>(*this);
                        else if (sCtrlClass == ControllerTwistFrontSteerPID::class_name())
                                controller_ =
                                        std::make_shared<ControllerTwistFrontSteerPID>(*this);
                        else if (sCtrlClass == ControllerFrontSteerPID::class_name())
                                controller_ = std::make_shared<ControllerFrontSteerPID>(*this);
                        else
                                THROW_EXCEPTION_FMT(
                                        "[DynamicsAckermann] Unknown 'class'='%s' in "
                                        "<controller> XML node",
                                        sCtrlClass.c_str());

                        controller_->load_config(*xml_control);
                }
        }
        // Default controller:
        if (!controller_)
                controller_ = std::make_shared<ControllerRawForces>(*this);
}

// See docs in base class:
std::vector<double> DynamicsAckermann::invoke_motor_controllers(
        const TSimulContext& context)
{
        // Longitudinal forces at each wheel:
        std::vector<double> out_torque_per_wheel;
        out_torque_per_wheel.assign(4, 0.0);

        if (controller_)
        {
                // Invoke controller:
                TControllerInput ci;
                ci.context = context;
                TControllerOutput co;
                controller_->control_step(ci, co);
                // Take its output:
                out_torque_per_wheel[WHEEL_RL] = co.rl_torque;
                out_torque_per_wheel[WHEEL_RR] = co.rr_torque;
                out_torque_per_wheel[WHEEL_FL] = co.fl_torque;
                out_torque_per_wheel[WHEEL_FR] = co.fr_torque;

                // Kinematically-driven steering wheels:
                // Ackermann formulas for inner&outer weels turning angles wrt the
                // equivalent (central) one:
                computeFrontWheelAngles(
                        co.steer_ang, wheels_info_[WHEEL_FL].yaw,
                        wheels_info_[WHEEL_FR].yaw);
        }
        return out_torque_per_wheel;
}

void DynamicsAckermann::computeFrontWheelAngles(
        const double desired_equiv_steer_ang, double& out_fl_ang,
        double& out_fr_ang) const
{
        // EQ1: cot(d)+0.5*w/l = cot(do)
        // EQ2: cot(di)=cot(do)-w/l
        const double w = wheels_info_[WHEEL_FL].y - wheels_info_[WHEEL_FR].y;
        const double l = wheels_info_[WHEEL_FL].x - wheels_info_[WHEEL_RL].x;
        ASSERT_(l > 0);
        const double w_l = w / l;
        const double delta =
                b2Clamp(std::abs(desired_equiv_steer_ang), 0.0, max_steer_ang_);

        const bool delta_neg = (desired_equiv_steer_ang < 0);
        ASSERT_LT_(delta, 0.5 * M_PI - 0.01);
        const double cot_do = 1.0 / tan(delta) + 0.5 * w_l;
        const double cot_di = cot_do - w_l;
        // delta>0: do->right, di->left wheel
        // delta<0: do->left , di->right wheel
        (delta_neg ? out_fr_ang : out_fl_ang) =
                atan(1.0 / cot_di) * (delta_neg ? -1.0 : 1.0);
        (delta_neg ? out_fl_ang : out_fr_ang) =
                atan(1.0 / cot_do) * (delta_neg ? -1.0 : 1.0);
}

// See docs in base class:
mrpt::math::TTwist2D DynamicsAckermann::getVelocityLocalOdoEstimate() const
{
        mrpt::math::TTwist2D odo_vel;
        // Equations:

        // Velocities in local +X at each wheel i={0,1}:
        // v_i = vx - w_veh * wheel_{i,y}  =  w_i * R_i
        // Re-arranging:
        const double w0 = wheels_info_[WHEEL_RL].getW();
        const double w1 = wheels_info_[WHEEL_RR].getW();
        const double R0 = wheels_info_[WHEEL_RL].diameter * 0.5;
        const double R1 = wheels_info_[WHEEL_RR].diameter * 0.5;

        const double Ay = wheels_info_[WHEEL_RL].y - wheels_info_[WHEEL_RR].y;
        ASSERTMSG_(
                Ay != 0.0,
                "The two wheels of a differential vehicle cannot be at the same Y "
                "coordinate!");

        const double w_veh = (w1 * R1 - w0 * R0) / Ay;
        const double vx_veh = w0 * R0 + w_veh * wheels_info_[WHEEL_RL].y;

        odo_vel.vx = vx_veh;
        odo_vel.vy = 0.0;
        odo_vel.omega = w_veh;

#if 0  // Debug
        {
                mrpt::math::TTwist2D gt_vel = this->getVelocityLocal();
                printf("\n gt: vx=%7.03f, vy=%7.03f, w= %7.03fdeg\n", gt_vel.vx, gt_vel.vy, mrpt::RAD2DEG(gt_vel.omega));
                printf("odo: vx=%7.03f, vy=%7.03f, w= %7.03fdeg\n", odo_vel.vx, odo_vel.vy, mrpt::RAD2DEG(odo_vel.omega));
        }
#endif
        return odo_vel;
}