Rhinoceros is not an automatic Reverse Engineering software.
In general, you will use the point cloud or polygon mesh as a reference to re-model 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.
A tutorial on the built-in functions in Rhino can be found here: http://download.rhino3d.com/download.asp?id=ScanCleanupRemodel
There are also some plug-ins available which help there reverse engineering process.
RhinoResurf new version has a lot of improvements: http://www.resurf3d.com/products.htm
RhinoReverse also is a plugin with promise: http://www.rhinoreverse.icapp.ch/english/index.html
Additional tools can be found at for Reverse Engineering at http://www2.rhino3d.com/resources/default.asp?category=13
And Geomagic Studio http://www.geomagic.com/en/products/studio/
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 PointCloudSection command in Rhino to reverse engineer curves first, then use those curves to construct NURBs surfaces.
Look here and the following pages: http://www.rhino3.de/design/modeling/reengineering/
To navigate, click the little text angles at the very bottom right of each page.
There are a few possibilities for doing this:
SMURF Plug-in for Rhino 3.0, http://www2.rhino3d.com/resources/display.asp?language=&listing=93 Smurf is a Rhino plug-in that allows for the interactive conversion of polygonal meshes to NURBs surface patches.
The SMURF plug-in requires a polygonal mesh. So, if you have a point cloud, you would need to convert the point cloud to a mesh first.
* Focus Reverse Engineering (formerly Paraform): polygonal and surface/solid tools. http://www.metris.com/products/point_cloud_software/focus_reverse_engineering/
Assuming you want a high quality surface on a complex product, about 2 years of professional experience should do the trick! but maybe for somthing where surface quality doesn't matter, or a very simple shape, SMURF etc. could do the trick. Without seeing the model or knowing what your project is, most people use the point cloud data as reference to create a model from scratch using good modelling techniques, combined with having to exactly match the scan data to the tolerence your after, i.e very hard!
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 Version 4.0.
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