Can't see quiver plot

I'm currently trying to make a code of potential field for path planning.

I defined potential energy(u_att, u_rep) and then force(fxa,fya,fxr,fyr) by using 'gradient'.

To the best of my knowledge, force vector(fxa,fya,fxr,fyr) is properly calculated,

but when I plot that force vector with 'quiver', I couldn't see anything on the plot.

How can I fix this?

Code for potential field is attached below

Thank you.

close all; clear; clc;
figure, hold on;
axis([0 100 0 100]), axis square, box on;
xlabel('x'), ylabel('y');

obslist = [60 60 15;
           20 40 7;
           70 30 5];  
    
x_start = [10 10];
x_goal = [90 90];

plot(x_start(1),x_start(2),'rx','linewidth',2);
plot(x_goal(1),x_goal(2),'bo','linewidth',2);
angs = (0:pi/50:2*pi)';
xpu = cos(angs); ypu = sin(angs);

for i=1:size(obslist,1)
    xp = obslist(i,1) + obslist(i,3)*xpu;
    yp = obslist(i,2) + obslist(i,3)*ypu;
    fill(xp,yp,'y');
    plot(xp,yp,'k');
end
% Above code is from KAIST Spring 2023 ME652 lecture
% -------------------------------------------------------------------------

slice = 1;
[X, Y] = meshgrid(0:slice:100, 0:slice:100);

Ka = 5;
u_att = 0.5*Ka*sqrt((X-x_goal(1)).^2 + (Y-x_goal(2)).^2);
[fxa,fya] = gradient(u_att,slice,slice);

Kr = 500;
u_rep = zeros(size(X));
for i=1:size(obslist,1)
    u_rep = u_rep + 0.5.*Kr*(1./sqrt((X-obslist(i,1)).^2 + (Y-obslist(i,2)).^2) - 1./sqrt((obslist(i,3)+2))).^2;
end
[fxr,fyr] = gradient(u_rep,slice,slice);

fX = - fxr - fxa;
fY = - fyr - fya;
quiver(X,Y,fX,fY, 'k')

% contour(X,Y,u_att+u_rep,25)

Answer 1

[chicken vector]

Because there are too many arrows and they overlap, causing the automatic scaling to not display anything.

Set the scale to 'off'with:

quiver(X,Y,fX,fY,0)

And adjust the values of fX and fY accordingly.

You can see an example in the comments.

[chicken vector]

close all; clear; clc;
figure, hold on;
axis([0 100 0 100]), axis square, box on;
xlabel('x'), ylabel('y');
obslist = [60 60 15;
           20 40 7;
           70 30 5];  
    
x_start = [10 10];
x_goal = [90 90];
plot(x_start(1),x_start(2),'rx','linewidth',2);
plot(x_goal(1),x_goal(2),'bo','linewidth',2);
angs = (0:pi/50:2*pi)';
xpu = cos(angs); ypu = sin(angs);
for i=1:size(obslist,1)
    xp = obslist(i,1) + obslist(i,3)*xpu;
    yp = obslist(i,2) + obslist(i,3)*ypu;
    fill(xp,yp,'y');
    plot(xp,yp,'k');
end
% Above code is from KAIST Spring 2023 ME652 lecture
% -------------------------------------------------------------------------
slice = 1;
[X, Y] = meshgrid(0:slice:100, 0:slice:100);
Ka = 5;
u_att = 0.5*Ka*sqrt((X-x_goal(1)).^2 + (Y-x_goal(2)).^2);
[fxa,fya] = gradient(u_att,slice,slice);
Kr = 500;
u_rep = zeros(size(X));
for i=1:size(obslist,1)
    u_rep = u_rep + 0.5.*Kr*(1./sqrt((X-obslist(i,1)).^2 + (Y-obslist(i,2)).^2) - 1./sqrt((obslist(i,3)+2))).^2;
end
[fxr,fyr] = gradient(u_rep,slice,slice);
fX = - fxr - fxa;
fY = - fyr - fya;
quiver(X,Y,fX/5,fY/5,0,'Color','k')

[기홍 박]

Thanks for your help!

Answer 2

[Chunru]

figure, hold on;
axis([0 100 0 100]), axis square, box on;
xlabel('x'), ylabel('y');
obslist = [60 60 15;
           20 40 7;
           70 30 5];  
    
x_start = [10 10];
x_goal = [90 90];
plot(x_start(1),x_start(2),'rx','linewidth',2);
plot(x_goal(1),x_goal(2),'bo','linewidth',2);
angs = (0:pi/50:2*pi)';
xpu = cos(angs); ypu = sin(angs);
for i=1:size(obslist,1)
    xp = obslist(i,1) + obslist(i,3)*xpu;
    yp = obslist(i,2) + obslist(i,3)*ypu;
    fill(xp,yp,'y');
    plot(xp,yp,'k');
end

% Above code is from KAIST Spring 2023 ME652 lecture
% -------------------------------------------------------------------------
slice = 1;
[X, Y] = meshgrid(0:slice:100, 0:slice:100);
Ka = 5;
u_att = 0.5*Ka*sqrt((X-x_goal(1)).^2 + (Y-x_goal(2)).^2);
[fxa,fya] = gradient(u_att,slice,slice);
Kr = 500;
u_rep = zeros(size(X));
for i=1:size(obslist,1)
    u_rep = u_rep + 0.5.*Kr*(1./sqrt((X-obslist(i,1)).^2 + (Y-obslist(i,2)).^2) - 1./sqrt((obslist(i,3)+2))).^2;
end
[fxr,fyr] = gradient(u_rep,slice,slice);
fX = - fxr - fxa;
fY = - fyr - fya;
% quiver(X,Y,fX,fY, 'k')
figure
quiver(X,Y,fX,fY,0)

% Check your code, fX and fY has inf values so that the autoscale is not
% working
max(fX(:)),max(fY(:))

ans = Inf

ans = Inf

[기홍 박]

Thanks for your help!