Important: See also James Carruthers' excellent explanation of display mesh problems

Note: Please feel free to contribute and share your meshing expertise and settings secrets! If you have some program- or process- specific export mesh settings, we can perhaps create a page with those…

Although Rhino is a NURBs surface modeler, it uses polygon meshes created from those surfaces for visualization purposes - so what you see on the screen when the model is shaded is in reality a special, invisible polygon mesh (the “render mesh”) that is attached to the actual NURBs surface.

Why? For quick shading and rendering. But while a mesh has the advantages of shading speed and adjustability, there is a disadvantage. The render mesh is always an approximation of the surface, so there are almost always gaps between the faceted render mesh and the actual smooth surface.

The same meshing engine in Rhino is used in the creation of analysis meshes for the functions like Draft Analysis and Curvature Analysis, EMap, etc., and by the Mesh command (Tools > Polygon Mesh > From NURBs Object), which creates a “real” mesh object directly from a NURBs object.

Exporting from Rhino with certain polygon-based formats (such as .stl) will also create mesh objects (in the exported file). Although you can't edit these in the original Rhino file, you do have the same group of mesh density settings to control how they are created.

The functions that create real, editable meshes like Mesh and Export (.stl) are very important in many applications, as other “downstream” programs or processes often need polygon mesh objects to work with.

All of the types of mesh objects can exist simultaneously in one file, they do not affect one another and each can have its own settings. Although all the meshes are created with the same engine, there are a couple of important differences between them.

• The render meshes created on NURBs surfaces and polysurfaces for visualization purposes (by using Shaded or Rendered Viewport) are not user accessible or editable, and cannot be separated from the NURBs object they were created from. They can be deleted by using the ClearAllMeshes command, and regenerated by using the RefreshShade command or by changing the settings (at File > Properties > Mesh) (which forces a global regeneration of all render meshes).
• The analysis meshes are similar to the render meshes in that they are not editable, and cannot be separated from their NURBs object. They simply have another set of controls and exist separately from the render meshes. You can see them temporarily, however, when you use the “adjust mesh” button or the “preview” button in the settings panel on the dialog boxes for the Analysis commands.
• The meshes created by the Mesh command are visible and editable, and separate from the NURBs objects they were created from. They are objects in their own right, and can be seen and edited with the various Rhino commands that apply to meshes (see Bonus > Mesh), and can be exported to in the polygon mesh formats like STL, DXF, 3DS, and OBJ.
• Meshes created during Save and Export (such as .STL) have the same mesh settings dialogs (“Detailed Controls”) as the other types. You can also see them temporarily when you use the “preview” button in the settings panel, but they are not stored in the original file (only exported).

Willem: When meshing an object for export I always first create a mesh and look at it in the viewport Flat Shade mode (FlatShade command) before exporting it to the desired format. The Flat Shade mode “Shades the current viewport with no smoothing so the individual (render)mesh faces are visible”.

The controls for different mesh types are virtually identical. The controls for the Render Mesh settings are part of the .3DM file's properties, they are global for the whole model. When exporting to a mesh format like STL, DXF, 3DS, and OBJ you can alternatively use simple controls, like a slider. The detailed controls for all are identical, and are described further below.

The render mesh (display mesh) settings can be found at File > Properties > Mesh. Rhino offers you 2 “standard” settings, “jagged and faster” and “smooth and slower”, as well as “custom”, which lets you access the detailed controls. The “simple” controls for the others are displayed at the moment you invoke the command and are just a slider: less ↔ more polygons. The “detailed controls” for the others are all the same.

The default for render meshes is “jagged and faster”, which is fine for quick visualization, but not very good for anything else.

The “smooth and slower” theoretically offers finer resolution at the expense of longer meshing times, but in practice, even though it does take longer, frankly, it may still leave visible gaps where you don't want them, so you are advised to try the “custom” settings instead.

The default “simple” slider settings for analysis meshes as well as Mesh and Export is “somewhere in the middle”…

The default setting for the special STL Export dialog is the value of Absolute Tolerance at File > Properties > Units.

If you really want to control your meshing process, here is where you need to start!

There are seven numerical settings and 3 check boxes. Each one has a different method of mesh control and some of them can work together. The interactions and combined effects of these settings is complex to understand. Individually they are well described in the Help however, and reading this info carefully will give you a good idea of what each one does.

A copy of the Rhino Mesh Help page can also be found here.

Below are quick custom setting suggestions that have been known to work, they are for you to experiment with.

Personally, I use the following detailed mesh settings: