Mesh to nurbs help

For some reason it makes the contours not like topo line… do you know why ?

Contouring a mesh results in polylines. Contouring a NURBS surface results in (smooth) NURBS curves.

https://wiki.mcneel.com/rhino/meshtonurb

As per the above article, MeshToNurb is absolutely not recommended for meshes with many polygons. In any case, contouring that will give you the same result as contouring a MeshToNurb produced polysurface, so doing that is useless.

If you want smooth topo curves either you need to smooth them via something like FitCrv or you can for example drape a surface over the mesh and then Contour that.

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Here it’s the next challenge. I have a lot of contour lines that are open. To close them requires a lot of manual work, drawing the missing part of the poly line. Any advice ?
My first idea was to convert MeshToNURB and extract the borders of the nurb. Not sure about the good solution.
Thank you and Happy new year!
sv

MeshToNURB replaces each mesh face with a separate NURBS surface with exactly the same shape as the mesh face. I do not understand how it will help solve your problems.

If the problem is gaps between polycurves then the Connect command may help. http://docs.mcneel.com/rhino/6mac/help/en-us/index.htm#commands/connect.htm?

If the problem is a single gap in a polycurve which should be closed then the CloseCrv command may help. http://docs.mcneel.com/rhino/6mac/help/en-us/index.htm#commands/closecrv.htm%3FTocPath%3DEdit%20objects|Curves|_____2

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You can maybe create the missing parts (I suppose you basically want to close the edges) using the _contour command and than join the lines with the already existing ones.