How can I generated curve that match mesh line generated by ¡°3dmesh¡±

When generated a surface with (command "3dmesh" "4" "3" point11 point12
point13 point21 point22 point23 point31 point32 point33 point41 point42
point43)

(command "surfu" 100);

(command "surfv" 80);

(command "surftype" 6);

and I want to draw the skeleton line of the surface, so I use(command
"spline" point11 point12 point13 """"""); but the line that generated by
¡°spline¡± doesn¡¯t match (the same as) the mesh line that ¡°3dmesh¡±
generated.

How can I generated curve that match mesh line generated by ¡°3dmesh¡±

 

Try setting the Spline fit tolerance to 0

 

I used "splinedit" to set the fit tolerance to zero,but It's seems didn't
worked.
I wonder if I have the right way to set spline tolerance to 0.If I didn't
,can you show me the details.
Or else is there any other method to draw an acute skeleton line of "mesh"
surface.
RICHARD

 

if you have the points , why not to use 3dpoly????

 

Cause I divided the mesh by (command "surfu" 100);
(command "surfv" 80); so I only know the key point ,what I need is the NURBS
line that fit the "3dmesh" generated surface.