Question

Matlab help? Setting a length of a line to 1?
So I have these two planes intersecting, and a line describes their intersection (right?)
P0 = [0 0 0];
N1 = [-2 1 2];
N2 = [1 1 1];
plane(P0, N1),
hold on,
plane(P0, N2),
L = cross(N1, N2);
arrow3(P0,L),
view(68,30),
hold off,
I need to set the blue line's length to 1. How do I do this?

Answer 1

The blue line being arrow 3 as found in this code:
function out = arrow3(P,V,color)

if nargin < 3
color = 'b';
end

x0 =P(1); y0 = P(2); z0 = P(3);
a = V(1); b = V(2); c = V(3);
l = max(norm(V), eps);

x = [x0 x0+a];
y = [y0 y0+b];
z = [z0 z0+c];
hchek = ishold;
plot3(x,y,z,color)
hold on
h = l - min(.2*l, .2) ;
v = min(.2*l/sqrt(3), .2/sqrt(3) );

upper = [h, v*tan(pi/6), 0]';
lower = [h, -v*tan(pi/6), 0]';

r = sqrt(a^2 +b^2);

if r > 0
col1 = [a b c]/l;
col2 = [-b/r, a/r, 0];
col3 = [-a*c/(l*r), -b*c/(l*r), r/l];
Q = [col1; col2; col3]' ;

else
if c > 0
Q = [0 0 -1; 0 1 0; 1 0 0];
else
Q = [0 0 1; 0 1 0; -1 0 0];
end

end

p = Q*upper; q = Q*lower;

plot3([x0+p(1), x0+a], [y0+p(2), y0+b], [z0+p(3), z0+c], color)
plot3([x0+q(1), x0+a], [y0+q(2), y0+b], [z0+q(3), z0+c], color)

if hchek == 0
hold off
end