How to match Nurbs surfaces


This might sound silly to the experts here, but I want to know how I can get two surfaces that I have created using lines + points and patch command to match at the common edge? I have used the same common line to create both the surfaces, but when I zoom in, they don’t match. This then creates a problem for me when I try to join the surfaces in order to make a closed object which I can then export as a stl file.
I am attaching two images of the surfaces that I am talking of. Please help. Thanks!


patched surface are generally not the most exact maybe you can use edge surface or network surface or sweep. those commands will create precise boundaries. you can also post a part of your file if you want somebody to have a look at it.


Thank you very much for the response. Let me try with the alternative methods you have suggested, first.


Hi. I did try both the methods. However, my problem is that I have to give depth into the area that falls in between the lines and I was doing this through patch command since I can select both edge curves and points through which I could fit the surface through. Attaching a reference shaded view to explain the nature of the final surface that I am looking at. This kind of surface doesn’t get generated with edgesrf and netwroksrf commands.

Given below is the ghosted view of the same thing, with the curves and points through which the surface is to be generated highlighted in yellow.

Ultimately, this object is to be sent as an STL file to a 3 -Axis router and will be produced in sandstone as a wall tile.


creates surface points which are not usable at least not in this matter. the advantage of and is that you can very well use the points to edit the surface for your matters.

network and sweep would also allow you to define your “depth” with an exact curve. i really would not use patch at all if possible. its the very very last resort to create a surface if you want full control over the process.

(David Cockey) #6

Try using Patch with a “Starting surface” and the “Preserve edges” options.

Use EdgeSrf to create a starting surface which matches the boundary curves. Run Patch and select the interior points and curves to fit the surface to. Click on the “Select starting surface” button and select the created surface. Make sure the “Preserve edges” option is checked. Click on OK. The surface created should match the boundary curves although it may extend outside of the boundary curves and need to be trimmed to the boundary curves.

You may need to experiment with the value of “Starting surface pull” in Patch. A smaller value will usually make the result fit closer to the interior points and curves, but may result in more wiggles in the surface. You may also need to rebuild the starting surface to have more control points before running Patch to improve the fit to the interior points and curves but possibly with a less smooth result. Experiment.

(David Cockey) #7

If you want sharp creases along arbitrary curves in the interior you will need to create individual surfaces.


This kind of surface get similar generated in minutes with Rhino -> Gimp2(Link) -> ZSurf(Link) -> Back to Rhino as .IGS (untrimmed surface).

  • Fast for creating
  • Untrimmed surface
  • No sharp details
  • Too many iso lines for detail
  • big mesh size

In Rhino:

  1. Activate Top View
  2. Select Curves and execute commands:
  3. _ZoomSelected, Escape for Unselect
  4. _ShowZBuffer
  5. _VieCaptureToFile (.bmp) or render to ZBuffer as .bmp

In Gimp2:

  1. Open .bmp file previous created in Rhino and execute commands:
  2. “Shift + O” and inside picture click on black area (selection by color black all areas, or “U” one or more areas)

…Optional Otherwise at next by step 6.
3. “Strg + I” (invert selection)
4. Menu -> Image -> Fit Canvas to Selection (resize to image size:)
5. “Strg + I” (invert selection)

6. “L” Activates Gradient Fill use option Fordeground Color Black Bacground White / Shape Shaped(Spherical or Angular)

7. Drag mouse on picture and Gradient Fill is now working

8. Unselect all adjust smoothness from Menu -> Filters -> Blur -> Gaussian Blur

9. Adjust color from Menu -> Color -> Curves or Contrast …or apply other filter

10.Export as .BMP Compability Options Checked -> Advanced -> 24 bits
!!! Save as 32 bit in Gimp is not compatible with ZSurf, but It goes with detour, must be resaved with a compatible program example XNView

In ZSurf:

  1. Open previous exported image
  2. Execute Process
  3. Go to ZSurf directory and import new created file SRF.IGS in to Rhino
  4. In Rhino select new Surface and adjust Custom Mesh for smoothing (or global), disable -> Show Isocurve, set Viewport to Shaded or Rendered

…Scale it back and edit


You can make similar surface in two simple steps: Gaussian Blur in Photoshop followed by Heightfield in Rhino.