Rhino is not an automatic reverse engineering software.
Generally, you will use the point cloud or polygon mesh as a reference to remodel the object with NURBs surfaces.
You can extract section curves from a point cloud (PointCloudSection command), or from a polygon mesh with Section or Contour.
There are also some plug-ins available which help the reverse engineering process.
The Patch command is the only tool you can directly use to create a surface from a set of points. But you could also use the PointCloudSection command in Rhino to reverse engineer curves first, then use those curves to construct NURBs surfaces.
Look here and the following pages for applications that automatically create NURBS surfaces from point clouds or meshes. To navigate, click the little text angles at the very bottom right of each page.
Reverse engineering is about the hardest thing to do in Rhino, depending on what the scanned item is. I've done it and it is not an easy or particularly enjoyable process, unless it's a terrain map in which case it should be feasible to get something with Patch. My advice would be to not undertake this point cloud to NURBs task unless absolutely necessary. (There are CAM programs that can take mesh files, if that's the problem.) And if you do need to, then either get help from someone with the Rhino experience–there's no trick, you just have to know Rhino really really well– or get specialized reverse engineering software needed to do it in a reasonable time frame.
This PDF file describes the process of cleaning up a scanned mesh and making it ready for STL printing. Additionally, the mesh is “reverse engineered” and replaced with NURBs surfaces, all in Rhino 4.0.
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