main/src/georegression/metric/Distance3D_F64.java
public static double distance( LineParametric3D_F64 l0,
								   LineParametric3D_F64 l1 ) {
		double x = l0.p.x - l1.p.x;
		double y = l0.p.y - l1.p.y;
		double z = l0.p.z - l1.p.z;

		// this solution is from: http://local.wasp.uwa.edu.au/~pbourke/geometry/lineline3d/
		double dv01v1 = MiscOps.dot( x,y,z, l1.slope );
		double dv1v0 = MiscOps.dot( l1.slope, l0.slope );
		double dv1v1 = MiscOps.dot( l1.slope, l1.slope );

		double bottom = MiscOps.dot( l0.slope, l0.slope ) * dv1v1 - dv1v0 * dv1v0;
		double t0;

		if( bottom == 0 ) {
			// handle parallel lines
			t0 = 0;
		} else {
			t0 = (dv01v1 * dv1v0 - MiscOps.dot( x,y,z, l0.slope ) * dv1v1)/bottom;
		}

		// ( d1343 + mua d4321 ) / d4343
		double t1 = ( dv01v1 + t0 * dv1v0 ) / dv1v1;

		double dx = ( l0.p.x + t0 * l0.slope.x ) - ( l1.p.x + t1 * l1.slope.x );
		double dy = ( l0.p.y + t0 * l0.slope.y ) - ( l1.p.y + t1 * l1.slope.y );
		double dz = ( l0.p.z + t0 * l0.slope.z ) - ( l1.p.z + t1 * l1.slope.z );

		// round off error can make distanceSq go negative when it is very close to zero
		double distanceSq = dx * dx + dy * dy + dz * dz;
		if( distanceSq < 0 )
			return 0;
		else
			return Math.sqrt( distanceSq );
	}
public static double distance( LineParametric3D_F64 l0,
								   LineParametric3D_F64 l1 ) {
		double x = l0.p.x - l1.p.x;
		double y = l0.p.y - l1.p.y;
		double z = l0.p.z - l1.p.z;

		// this solution is from: http://local.wasp.uwa.edu.au/~pbourke/geometry/lineline3d/
		double dv01v1 = MiscOps.dot( x,y,z, l1.slope );
		double dv1v0 = MiscOps.dot( l1.slope, l0.slope );
		double dv1v1 = MiscOps.dot( l1.slope, l1.slope );

		double bottom = MiscOps.dot( l0.slope, l0.slope ) * dv1v1 - dv1v0 * dv1v0;
		double t0;

		if( bottom == 0 ) {
			// handle parallel lines
			t0 = 0;
		} else {
			t0 = (dv01v1 * dv1v0 - MiscOps.dot( x,y,z, l0.slope ) * dv1v1)/bottom;
		}

		// ( d1343 + mua d4321 ) / d4343
		double t1 = ( dv01v1 + t0 * dv1v0 ) / dv1v1;

		double dx = ( l0.p.x + t0 * l0.slope.x ) - ( l1.p.x + t1 * l1.slope.x );
		double dy = ( l0.p.y + t0 * l0.slope.y ) - ( l1.p.y + t1 * l1.slope.y );
		double dz = ( l0.p.z + t0 * l0.slope.z ) - ( l1.p.z + t1 * l1.slope.z );

		// round off error can make distanceSq go negative when it is very close to zero
		double distanceSq = dx * dx + dy * dy + dz * dz;
		if( distanceSq < 0 )
			return 0;
		else
			return Math.sqrt( distanceSq );
	}
Distance of the closest point between two lines.  Parallel lines are correctly
handled.

@param l0 First line. Not modified.
@param l1 Second line. Not modified.
@return Distance between the closest point on both lines.