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HelperKinematicVehicle.m
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HelperKinematicVehicle.m
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%HelperKinematicVehicle Simulation of kinematic behavior of vehicle.
% This is a helper class that manages pose update for a vehicle with
% kinematics defined by the bicycle model.
%
% NOTE: The name of this class and it's functionality may change without
% notice in a future release, or the class itself may be removed.
%
% vehicle = HelperKinematicVehicle(vehicleDims) returns a kinematics
% model of vehicle. vehicleDims is a vehicleDimensions object storing
% vehicle dimensions.
%
% HelperKinematicVehicle properties:
% VehicleDimensions - Vehicle dimensions
% MaxSteeringAngle - Maximum steering angle of the vehicle
% Pose - Current vehicle pose [x, y, theta] (read-only)
% Velocity - Current velocity (in meters/second) (read-only)
% SteeringAngle - Steering angle (read-only)
% AccelCmd - Acceleration command (in meters/second^2) (read-only)
% DecelCmd - Deceleration command (in meters/second^2) (read-only)
% Direction - Driving direction (read-only)
%
% HelperKinematicVehicle methods:
% setPose - Set vehicle pose
% setDirection - Set driving direction
% setVelocity - Set vehicle velocity
% setControlCommand - Set control commands
% enableLimitedCommandTime - Enable control command timeout
% updateKinematics - Propagate vehicle kinematic model
%
% See also HelperVehicleSimulator, vehicleDimensions.
%
% Copyright 2017-2018 The MathWorks, Inc.
classdef HelperKinematicVehicle < handle
properties (SetAccess = private)
%Pose Current vehicle pose [x, y, theta]
Pose
%Velocity Current velocity (in meters/second)
Velocity
%Steering angle
SteeringAngle
%AccelCmd Acceleration command (in meters/second^2)
AccelCmd
%DecelCmd Deceleration command (in meters/second^2)
DecelCmd
%Direction Driving direction: 1 for forward motion and -1 for
% reversed motion
Direction
end
properties
%VehicleDimensions A vehicleDimensions object
% A vehicleDimensions object encapsulating dimensions of the
% vehicle. Vehicle dimensions must be defined in the same world
% units as the costmap.
VehicleDimensions
%MaxSteeringAngle Maximum steering angle
%
% Default: 45 (deg)
MaxSteeringAngle = 45
end
properties (Access = private, Dependent)
%MinimumTurningRadius
% Minimum turning radius of vehicle
MinTurningRadius
end
properties (Access = private)
%TimeSinceLastCmd Elapsed time since the last velocity command
% This counts the time (in second), since the last unique
% velocity command was received.
TimeSinceLastCmd = tic
%MaxCommandTime The maximum time interval between velocity commands
% If more time (in seconds) than MaxCommandTime elapses between
% unique velocity commands, the vehicle is stopped.
% Default: 1 second
MaxCommandTime = 1
%EnableLimitedCommandTime Enable velocity command timeout.
EnableLimitedCommandTime = true;
end
%----------------------------------------------------------------------
% API
%----------------------------------------------------------------------
methods
%------------------------------------------------------------------
function obj = HelperKinematicVehicle(vehicleDims)
%HelperKinematicVehicle
% obj = HelperKinematicVehicle(vehicleDims) creates a
% kinematic vehicle simulator for a vehicle with dimensions
% specified in the vehicleDimensions object vehicleDims.
obj.VehicleDimensions = vehicleDims;
end
%------------------------------------------------------------------
function setPose(obj, pose)
%setPose Set the pose of the vehicle. It also set the control
% commands to zeros.
obj.Pose = reshape(pose,1,3);
obj.AccelCmd = 0;
obj.DecelCmd = 0;
obj.SteeringAngle = 0;
end
%------------------------------------------------------------------
function setVelocity(obj, velocity)
%setVelocity Set velocity of the vehicle
obj.Velocity = velocity;
end
%------------------------------------------------------------------
function setDirection(obj, direction)
%setDirection Set driving direction of the vehicle
obj.Direction = direction;
end
%------------------------------------------------------------------
function enableLimitedCommandTime(obj, enableLimitedCommandTime)
%enableLimitedCommandTime Enable velocity command timeout.
% enableLimitedCommandTime(obj, true) - Enable limited
% command time mode, vehicle's velocity is reset to zero if
% no new velocity commands arrive in the last MaxCommandTime
% seconds.
%
% enableLimitedCommandTime(obj, false) - Disable limited
% command time mode.
obj.EnableLimitedCommandTime = enableLimitedCommandTime;
end
%------------------------------------------------------------------
function setControlCommand(obj, ctrlCmd)
%setControlCommand Set vehicle speed and steering angle
%
% setControlCommand(obj, [accelCmd, decelCmd, steerCmd]) sets
% the control command for the kinematic vehicle.
obj.AccelCmd = ctrlCmd(1);
obj.DecelCmd = ctrlCmd(2);
obj.SteeringAngle = ctrlCmd(3);
obj.TimeSinceLastCmd = tic;
end
%------------------------------------------------------------------
function updateKinematics(obj, dt)
%updateKinematics Propagate the kinematic model of the vehicle
% in time by dt.
validateattributes(dt, {'numeric'}, {'nonnan', 'real', ...
'finite', 'scalar', 'nonempty'}, 'updateKinematics','dt');
% If no velocity command is received within some time, stop
% the vehicle.
if obj.EnableLimitedCommandTime && toc(obj.TimeSinceLastCmd) >...
obj.MaxCommandTime
obj.SteeringAngle = 0;
obj.Velocity = 0;
end
% Limit steering angle to maximum allowable value
delta = obj.SteeringAngle;
obj.SteeringAngle = sign(delta) * min(abs(delta), obj.MaxSteeringAngle);
if abs(obj.SteeringAngle) < 1e-5
obj.SteeringAngle = 0;
end
% Propagate vehicle state change based on velocities in rear
% wheel coordinate
% Integrate to obtain speed. Enforce speed not to cross zero.
speed = abs(obj.Velocity) + dt*(obj.AccelCmd - obj.DecelCmd);
obj.Velocity = max(speed, 0)*obj.Direction;
delta_theta = obj.Velocity/obj.VehicleDimensions.Wheelbase * sind(obj.SteeringAngle);
dx = dt*obj.Velocity*cosd(obj.Pose(3) + obj.SteeringAngle) + ...
dt*obj.VehicleDimensions.Wheelbase*sind(obj.Pose(3))*delta_theta;
dy = dt*obj.Velocity*sind(obj.Pose(3) + obj.SteeringAngle) - ...
dt*obj.VehicleDimensions.Wheelbase*cosd(obj.Pose(3))*delta_theta;
dtheta = dt * delta_theta;
% Update vehicle state accordingly
obj.Pose = obj.Pose + [dx dy rad2deg(dtheta)];
obj.Pose(3) = mod(obj.Pose(3), 360);
end
end
%----------------------------------------------------------------------
% Accessors
%----------------------------------------------------------------------
methods
%------------------------------------------------------------------
function r = get.MinTurningRadius(obj)
r = obj.VehicleDimensions.Wheelbase / tand(obj.MaxSteeringAngle);
end
end
end