Mesh to nurbs

I imported a DWG file to Rhino4, this model on the left hand side, looks like it was converted from .stl by the look of it (meshes):

I wanted to copy the border or circle of this 'circular base" but there are so many points I can not tell which is the exact midpoint of the base circle so I can redraw a circle again, I tried MeshtoNurb then “duplicate face border” the result is shown on the right side of the picture and is not what I want. Can anyone tell me what is the best way to obtain the circle of the base out the mesh?



Try drawing circle using 3Pt option, snapping to far spaced vertices of the outline of the mesh.
It may be easier to start with MeshOutline command on your meshes to just get the shape border polyline.



Hi Jarek,
Will give it a try, thanks!