If the shortest distance between two points is a straight line what is the shortest distance between two straight lines?

Answer 1

The question is curiously vague. Do the two lines exist in the same plane? If they do, then they must intersect somewhere -- unless they are parallel. For non-parallel lines, the distance between the two lines at the point of intersection is zero. For parallel lines, the shortest distance between them is the length of the line segment that is perpendicular to both. For intersecting lines, there is an infinite number of distances between the infinite number of pairs of points on the lines. But for any pair of points -- one point on line A and another on line B -- the shortest distance between them will still be a straight line. Given two lines in 3D (space) there are four possibilities # the lines are collinear (they overlap) # the lines intersect at one point # the lines are parallel # the lines are skew (not parallel and not intersecting) The question of "shortest distance" is only interesting in the skew case. Let's say p0 and p1 are points on the lines L0 and L1, respectively. Also d0 and d1 are the direction vectors of L0 and L1, respectively. The shortest distance is (p0 - p1) * , in which * is dot product, and is the normalized cross product. The point on L0 that is nearest to L1 is p0 + d0(((p1 - p0) * k) / (d0 * k)), in which k is d1 x d0 x d1.