bsplinecurve b1 3 5 0 4 1 1 2 1 3 1 4 4  0 0 0 1  1 2 0 1   2 2 0 1   2 2 0 1  3 2 0 1  4 2 0 1   5 4 0 1 
cvalue b1 2.0 x y z dx dy dz
set delta 0.01
set yvalue [dval y] 
set zvalue [dval z] 
repeat 100  {
	cmovetangent b1 2.0  x $yvalue $zvalue dx dy dz 1
        set yvalue [expr $yvalue + $delta ]
        set zvalue [expr $zvalue + $delta ]
        repaint }
renamevar b1 result
set length 8.3346946955628098

