RobotStudio/robot/demos/particlefilt.m


% Copyright (C) 1993-2017, by Peter I. Corke
%
% This file is part of The Robotics Toolbox for MATLAB (RTB).
% 
% RTB is free software: you can redistribute it and/or modify
% it under the terms of the GNU Lesser General Public License as published by
% the Free Software Foundation, either version 3 of the License, or
% (at your option) any later version.
% 
% RTB is distributed in the hope that it will be useful,
% but WITHOUT ANY WARRANTY; without even the implied warranty of
% MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
% GNU Lesser General Public License for more details.
% 
% You should have received a copy of the GNU Leser General Public License
% along with RTB.  If not, see <http://www.gnu.org/licenses/>.
%
% http://www.petercorke.com

%%begin

% Our localization system requires a number of components:
% * a vehicle
% * a map that defines the positions of some known landmarks in the world
% * a sensor, a range-bearing sensor in this case
% * a localization filter, specifically the Monte-Carlo style "particle filter"

% Creating the vehicle.  First we define the covariance of the vehicles's odometry
% which reports distance travelled and change in heading angle

V = diag([0.1, 1*pi/180].^2);

% then use this to create an instance of a Vehicle class
veh = Bicycle(V);

% and then add a "driver" to move it between random waypoints in a square
% region with dimensions from -10 to +10

veh.add_driver( RandomPath(10) );

% Creating the map.  The map covers a square region with dimensions from 
% -10 to +10 and contains 20 randomly placed landmarks
map = LandmarkMap(20, 10);

% Creating the sensor.  We firstly define the covariance of the sensor measurements
% which report distance and bearing angle
W = diag([0.1, 1*pi/180].^2);

% and then use this to create an instance of the Sensor class.
sensor = RangeBearingSensor(veh, map, 'covar', W, 'animate');
% Note that the sensor is mounted on the moving robot and observes the features
% in the world so it is connected to the already created Vehicle and Map objects.

% Create the filter.  The particle filter requires a likelihood function that maps 
% the error between expected and actual sensor observation to a weight.  The Toolbox 
% uses a 2D Gaussian for this and we need to describe it by a covariance matrix
L = diag([0.1 0.1]);

% The filter also needs a noise model to "drift" the particles at each step, that
% is the hypotheses are randomly moved to model the effect of uncertainty in the
% vehicle's pose
Q = diag([0.1, 0.1, 1*pi/180]).^2;
% the values of this matrix should be consistent with the vehicle uncertainty 
% model V given above.

% Now we create an instance of the particle filter class
pf = ParticleFilter(veh, sensor, Q, L, 1000);
% and connect it to the vehicle and the sensor and give estimates of the vehicle
% and sensor covariance (we never know this is practice).  The last argument
% is the number of particles that will be used.  Each particle represents a hypothesis
% about the vehicle's pose and a weight (or likeliness).

% Now we will run the filter for 200 time steps.  At each step the vehicle
% moves, reports its odometry and the sensor measurements and the filter updates
% its estimate of the vehicle's pose.  
%
% The green dots represent the particles.  We see that initially the pose
% hypotheses are very spread out, but soon start to cluster around the actual pose
% of the robot.  The pose is 3D (x,y, theta) so if you rotate the graph while the
% simulation is running you can see the theta dimension as well.
pf.run(100);
% all the results of the simulation are stored within the ParticleFilter object

% First let's plot the map
clf; map.plot()
% and then overlay the path actually taken by the vehicle
veh.plot_xy('b');
% and then overlay the path estimated by the filter
pf.plot_xy('r');
% which we see are pretty close once the filter gets going, the initial estimates
% (when the particles are spread widely) are not so good.

% The uncertainty of the estimate is related to the spread of the particles and
% we can plot that
figure; plot(pf.std); xlabel('time step'); ylabel('standard deviation'); legend('x', 'y', '\theta'); grid       
