# Surface changes in longitudinal direction (U) when only the point count in transver direction (V) is changed

Good day,

Added is a file with 2 surfaces on top of each other.
When I change the point count in the transvers (V) direction from 2 to 4, all points, except those in the ends move from position.
But, all former points have to keep their position.
Is there a way to do so?

Kind regards,

Dirk
surfaces.3dm (52.0 KB)

Hi Dirk - how are you changing the points? If using `Rebuild`, points will not stay put, but using `ChangeDegree` from 1 to 3 in V, will leave them alone.

-Pascal

Morning Pascal,

I do not only want to change the degree, but first of all the point count, and that is where the points move.
Now these forms are rather simple, so I’m able to move the points back in position again, but it would be a lot more work with a more complicated form.

Regards,

Dirk

Hi Dirk - that does not answer the question, how are you currently changing the point count?

-Pascal

Hallo Pascal,

Sorry for not answering your question. Yes, I did use “rebuild”, and thought that when using “change degree” only the degree would change, but I tried again this morning and see that when changing the degree, also the point count changes and the points stay in position.
Thanks, this solves my problem.

Regards,

Dirk

Hi Dirk - this may be useful in understanding why the result of `ChangeDegree` is more points:
https://wiki.mcneel.com/rhino/nurbs

-Pascal

Hi Pascal,

Understanding your link will take a while, but I’m glad things work the way I want it.

Regards,

Dirk

Rebuild always rebuilds a surface in both directions with uniform distribution of knots and all weights equal to one even if the number of points in one or both directions is unchanged. That means the shape will usually change in both directions.

RebuildUV rebuilds a surface only in the selected direction with uniform distribution of knots and all weights equal to one.

InsertKnot can be used to add knots and control points without changing the shape of a surface.

Hallo David,

Thanks. I still use the pull-down menus because I’m used to that.

But I see that under the “surface tools” button there is also the possibility to rebuild the surface in U and V direction.
This is exactly what I was looking for.

Regards,

Dirk

The button on the drop down menu is an alternative method of starting RebuildUV.

To find a button which starts a command go to Help for the command. It will show near the top how the command can be started.