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function demo_car()
initial=[3;3;0;0]
final=[0;0;0;0]
f = gcf() ;
f.pixmap = 'on' ;
toolbar(0,'off');
state=car_solve(initial,final);
display_car_trajectory(state)
endfunction
function state=car_solve(initial,final)
//
// CAR PACKING VIA FLATNESS AND FRENET FORMULAS
//
// explicit computation and visualisation of the motions.
//
// February 1993
//
// ............................................................
// : pierre ROUCHON <rouchon@cas.ensmp.fr> :
// : Centre Automatique et Systemes, Ecole des Mines de Paris :
// : 60, bd Saint Michel -- 75272 PARIS CEDEX 06, France :
// : Telephone: (1) 40 51 91 15 --- Fax: (1) 43 54 18 93 :
// :..........................................................:
//
// initial: initial position [x,y,theta,phi]
// final : final position [x,y,theta,phi]
// theta : the car angle
// phi : the front wheel angle
bigT = 1 ;//basic time interval for one smooth motion (s)
bigL = 1 ;// car length (m)
// computation of intermediate configuration
x0 = maxi(initial(1),final(2)) ....
+ bigL*abs(tan(initial(3))) ...
+ bigL*abs(tan(final(3))) ...
+ bigL*(abs(initial(2)-final(2))/bigL)^(1/2) ;
y0 = (initial(2)+final(2))/2 ;
intermediate=[x0,y0,0,0]'
// first polynomial curve
state=[matrix(initial,1,-1);
car_polynomial_curve(initial,intermediate,"direct")]
//
// second polynomial curve
state = [ state;
matrix(intermediate,1,-1)
car_polynomial_curve(final,intermediate,"reverse")
matrix(final,1,-1)]
endfunction
function state=car_polynomial_curve(initial,final,orient)
nbpt = 40 ; // sampling of motion
theta1 = initial(3) ; phi1 = initial(4) ;
da = initial(1)-final(1)
M = [da^3 da^4 da^5
3*da^2 4*da^3 5*da^4
6*da 12*da^2 20*da^3 ] ;
q = [initial(2)-final(2)
tan(theta1)
tan(phi1)/(bigL*(cos(theta1)^3))] ;
p = inv(M)*q ;
tau=(0:nbpt)'/nbpt
phi=tau.*tau.*(3-2*tau) ;
if orient=='reverse' then
a = (1-phi)*final(1) + phi*initial(1) ;
else
a = (1-phi)*initial(1) + phi*final(1) ;
end
da=a-final(1)
f= final(2)+ p(1).*da^3 + p(2).*da^4 + p(3).*da^5 ;
df = 3*p(1).*da^2 + 4*p(2).*da^3 + 5*p(3).*da^4 ;
ddf = 6*p(1).*da + 12*p(2).*da^2 + 20*p(3).*da^3 ;
k = ddf ./ ((1+df.*df)^(3/2)) ;
state=[ a f atan(df) atan(k*bigL)]
endfunction
function display_car_trajectory(state)
bigL=1
set figure_style new;xbasc();xselect()
a=gca()
drawlater()
a.isoview="on"
a.data_bounds=[mini(state(:,1))-0.5*bigL, mini(state(:,2))-1.5*bigL
maxi(state(:,1))+1.5*bigL, maxi(state(:,2))+1.5*bigL]
rect=matrix(a.data_bounds',-1,1)
xpoly(rect([1 3 3 1]),rect([2,2,4,4]),'lines',1)
C=build_car()
Cinit=[];Cend=[];Cinter=[];
for k=1:size(C,'*')
Cinit=[Cinit copy(C(k))];
Cinter=[Cinter,copy(C(k))];
Cend=[Cend,copy(C(k))]
end
// starting configuration
draw_car(Cinit,state(1,:))
// end configuration
draw_car(Cend,state($,:))
// intermediate configuration (inversion of velocity)
draw_car(Cinter,state(ceil(size(state,1)/2),:)) ;
// trajectory of the linearizing output
t1=polyline([state(1,1) state(1,2);state(1,1) state(1,2)]) ;
t1.line_style=2;
realtimeinit(0.1)
for i=1:size(state,1)
realtime(i)
drawlater()
draw_car(C, state(i,:))
t1.data=[t1.data;state(i,1) state(i,2)];
drawnow()
end
for i=(1:30)+size(state,1),realtime(i),end
xdel()
endfunction
function C=build_car()
//build the graphic object for the car
//
//the car
hcar=polyline([-2,7,8,8,7,-2,-2;-2,-2,-1,1,2,2,-2]'/6)
hcar.foreground=2
// rear wheels
hwheel1=polyline([[-1 1]/8; [1 1]/6]')
hwheel1.thickness=2
hwheel2=polyline([[-1 1]/8; -[1 1]/6]')
hwheel2.thickness=2
// front wheels
hwheel3=polyline([[7 9]/8;[1 1]/6]')
hwheel3.thickness=2
hwheel4=polyline([[7 9]/8;-[1 1]/6]')
hwheel4.thickness=2
//return vector of handle on the objects
C=[hcar,hwheel1,hwheel2,hwheel3,hwheel4]
endfunction
function draw_car(C,pos)
drawlater()
[x,y,theta,phi]=(pos(1),pos(2),pos(3),pos(4))
bigL=1
Rc=[cos(theta) sin(theta);-sin(theta) cos(theta)]
// the car
xy = [-2,-2;7,-2;8,-1;8,1;7,2;-2,2;-2,-2]/6
C(1).data=ones(xy)*diag([x;y])+bigL*xy*Rc
// rear wheels
xy=[[-1 1]/8; [1 1]/6]'
C(2).data=ones(xy)*diag([x;y])+bigL*xy*Rc
xy=[[-1 1]/8; -[1 1]/6]'
C(3).data=ones(xy)*diag([x;y])+bigL*xy*Rc
// front wheels
xy=[(1-cos(phi)/8) (1/6-sin(phi)/8)
(1+cos(phi)/8) (1/6+sin(phi)/8)]
C(4).data=ones(xy)*diag([x;y])+bigL*xy*Rc
xy=[(1-cos(phi)/8) (-1/6-sin(phi)/8)
(1+cos(phi)/8) (-1/6+sin(phi)/8)]
C(5).data=ones(xy)*diag([x;y])+bigL*xy*Rc
drawnow()
show_pixmap();
endfunction
function h=polyline(xy)
xpoly(xy(:,1),xy(:,2),'lines')
h=gce()
endfunction
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