Is "Slicing" a Mesh Possible


I’ve been away for a while, focusing on music, but getting back into CAD stuff.

I downloaded a mesh that I like and want to get it into NURBS surfaces. My plan is to take the mesh and take sections along X and Y, develop curves along them, and hopefully end up with a useable array of curves in the X and Y directions.

Is this a good way to do it, sort of old school, no smoke and mirrors? I drew a curve to show, but I want more of them in a grid pattern.


335platenurbs for Forum.3dm (441.2 KB)

not sure what you are aiming for, but i would use Meshoutline from the top view. that will give you a polyline from the outline and the inner parts to start with. hide the rest and take the straight curve off where the body hits the neck (that is to insure that this part does not get rebuilt since you want it later straight) and use RebuildCrvNonUniform, maybe use Fair on a tight tolerance to get the curve to behave. add the straight line back and join then take that to trim the later loft. with the middle curve you started add at least 2 more, flatten the points of these with setpoint for instance and loft. you might want to refine that to your likings of course, this is just a crude approximation. then use the outline curve from before go to top view and use this as a trim curve for the loft.


you can prject curves to a mesh, but they will be polycurves with many degree 1 segments joined at their ends.

you will need to rebuild them to get useful curves for surfacing.

Thanks, Kyle!

I found that this works pretty well, and faster than correcting a boatload of degree 1 curves. I split the mesh using a surface, hide or put on separate layers what I don’t care about at the moment, and the edge of the mesh (Green) shows on the surface , and I trace a curve (Cyan) over it, using the ortho lines as my 2nd point in from the end tangents.

I didn’t expect to press a button and have Rhino instantly solve my problem. I’m still learning a lot of commands, but probably won’t learn over 800 of them today!

I set the surface as the CPlane, and draw away. At some point the model will look like ice cubes.

Method I use:

Contour or Section the mesh to obtain polylines.

FitCrv the polylines to obtain curves.
Rhinoceros Help - FitCrv | Rhino 3-D modeling (

  • When the input to the FitCrv command is a polyline, the FitCrv command treats the polyline vertices as a list of points, and it tries to compute a curve that goes near the points but has a reasonable number of control points. The FitCrv command is meant for polylines with many closely spaced points.

Experimentation may be needed to find the toleance and angletolerence for FitCrv which provides desired results. I typically use a tight tolerance with FitCrv, and then Rebuild the curves with fewer control points and/or RemoveKnot to remove knots and control point in areas with less curvature.

FitCrv is better than Rebuild for this. FitCrv fits the curve using all the points while Rebuild selects and interpolates through number equal to the specified point count of approximately equally spaced points, which may be much less than the number of points in the input polycurve.

I tried contour, selected a polyline , did rebuild, selected the curve, tried curvaturegraph, and it shows a white line the same as the curve, no matter what scale I have , tried 1-40.

Did I break my copy of Rhino? Can someone try curvaturegraph on the file I uploaded? Thanks

One Curve.3dm (26.4 KB)

Try 100 to 140.

My bad…


yes but it depends… fitcrv can give a more accurate but very heavy result, especially if the mesh is very dense.

this can be good or bad depending on your needs, and must be evaluated on the fly on a case by case basis if fitcrv or rebuild is the tool to go for.

That is the reason I recommend FitCrv followed by Rebuild and/or RemoveKnot.

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Is what you and Kyle are discussing less complicated than the way I am planning on doing it?

To me, it’s sounding like a “forest from the trees” scenario.

I appreciate the discussion, though. I now know about a few more commands.

This is basically a reverse engineering task from Mesh to Surface. The Base surface is simply a slightly deformed plane with some complicated trims and cutouts. Exactly that scenario is tackled by the RROnePatch command from the RhinoReverse tools. No need to mess around with curves, simply extracted the base mesh from the thickened model and used RROnePatch on it:

RROnePatch-335platenurbs for Forum-v6.3dm (807.4 KB)

Thank you!

I’ll try it.

I have Version 7 and can’t find the command you mentioned. I guess that cool command disappeared due to an “upgrade”.

For me the Section command is quicker and less complicated than:

Using the curve from Section you can

I sometimes do that using InterpCrv. Other times I find using FitCrv followed by simplification is quicker.


RhinoReverse is a third party plug-in. Price appears to be over $1000, and does not appear to have been updated recently.

Simple way to obtain a NURBS surface from the mesh,

ExtractMeshPart the top surface mesh.

Patch command using the mesh as the input. Result is an untrimmed NURBS surface which will need to be trimmed later.

PointDeviation to check deviation of the NURBS surface from the input mesh. Use the mesh as the object to extract points from.

If the deviation of the surface from the mesh is too large use Patch again with increased number of spans.

Trim the surface to suit.

Patch with 4 spans in each direction resulted in deviation from the mesh of:
Total points: 818
Close point count: 818
Average distance: 0.01175141
Median distance: 0.008327913
Standard deviation: 0.01180596
Maximum distance: 0.09133587
Minimum distance: 6.142677E-05

335platenurbs for Forum DC01.3dm (2.3 MB)

If you have edge curves use the edge curves and the mesh as input to Patch. Use a small point spacing in Patch so that the edge curves will be closely match. The Automatic trim option in Patch may trim surface to suit. Or trim the surface separately.

Thanks David. I’ll keep on going as planned.