you are asking if a,b,c,d determine x,y,u,v. But clearly u/x = 2a, u/y = 2b, v/x = 2c, and v/y = 2d, so if you know a,b,c,d, you only know the ratios of u and v to x and y. so you could double u and v and x and y, and the same ratios would hold. So a,b,c,d do not determine x,y,u,v.