Problem with affine rectification

I have been trying to perform affine rectification using Matlab. By using Hough Lines I find two sets of parallel lines, I compute both of the vanishing points and then I find the vanishing line:

p1=[1056 2862 1];
p2=[1374 2692 1];
l1=cross(p1,p2);

p1=[2316 253 1];
p2=[2639 27 1];
l2=cross(p1,p2);

p1=[1149 2334 1];
p2=[1111 2833 1];
m1=cross(p1,p2);

p1=[1519 1602 1];
p2=[1532 2014 1];
m2=cross(p1,p2);

v1=cross(l1,l2);
v1=v1/v1(3)    // =1.0e+03 *   [-9.4067    8.4553    0.0010]
v2=cross(m1,m2);
v2=v2/v2(3);  // =1.0e+03 *    [1.4269   -1.3157    0.0010]
v_line = cross(v1,v2);
//

H = [1 0 0; 0 1 0; v_line(1)/v_line(3) v_line(2)/v_line(3) 1];

H_p=projective2d(H);
I_aff=imwarp(I, H_p);

The problem is that I_aff is exactly as the input image. Nothing happened. What am I doing wrong?

[Massimo Vassalli]

Have you solved this problem? Apparently I have the same issue.