A brief overview of Rhino's custom meshing settings and how they work

Note: For the sake of clarity, I have condensed the original page to a quick overview of the custom mesh settings. For people who want to know more, the detailed explanations are still available, they can now be found on this page. –Mitch 16.01.2013

The controls for the Render Mesh (display mesh) settings are part of the .3dm file's properties; they can be reached via (File > Properties > Mesh or Tools > Options > Mesh).

They are generally set globally for the whole model, but from V4 on, you can also override them on a per-object basis via the Properties panel.

Rhino offers you 2 standard settings, Jagged and Faster and Smooth and Slower, as well as Custom, which lets you access the detailed controls.

• Jagged and Faster is the default for render meshes — fine for general visualization purposes.

• Smooth and Slower offers better resolution at the expense of longer meshing times.
  
• (In V4, the smooth and slower setting did not work that well, in V5 it works better!)

• Custom allows the user the maximum flexibility in tailoring the mesh settings to their needs, at the expense of being a bit more complex to understand and set up.

See also James Carruthers' excellent explanation of polygon meshes used for display

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

When you check Custom in V5 you are first presented with a simple slider controlling the Density setting. Moving it to the left will result in a fewer polygons and a coarser mesh, to the right in more polygons and a finer mesh.

If you then push the Detailed Controls button, it will reveal all the other “granular” controls that will allow you to completely control the process. In V4, the granular controls are presented directly; the Density setting is not available as a slider.

There are seven numerical settings and three 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 are 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.

Please read the companion page to this one for detailed meshing info

Below is a basic start point for custom settings, you will need to do some experimentation with them on your models. If a setting is 0 or 0.0, it is turned off (not taken into a account).

Refine mesh checked
Jagged seams unchecked
Simple planes unchecked

• The maximum angle method forces more triangles in sharply curved areas. This way small features that fall below the max distance number will be subdivided a little. You may be able to get away with a little bigger max distance number letting the angle setting take over for the smallest objects/features.

• The maximum distance edge to surface method forces Rhino to create a mesh that is no further away from the surface than the specified value, which is in current file units. It allows Rhino to put fewer polygons in lower detail areas and more polygons in higher detail areas, resulting in a more efficient mesh.
• The minimum initial grid quads setting makes sure the flatter areas have enough polygons to look smooth.

The most important setting here is max distance edge to surface. This value is in file units and is scale (size) dependent - that means you will need to adjust it for the size and level of detail of the objects you model.

The setting will depend on what you're going to be using your mesh setting for. For general display purposes your value can be a bit bigger (coarser), as you're only visualizing the model on your screen, and less polygons mean faster meshing times and quicker display reaction when tumbling, zooming, etc. On the other hand, if you need to have more accurate meshing on very fine details for a hi-resolution render (or for manufacturing, perhaps), the value will need to be smaller (finer).

• If you are doing toaster oven sized objects, 0.01mm (.0005 in.) generally works out pretty well.

• For small highly detailed objects such as watches and jewelry, try something less, maybe .002mm (.00001 in).

• For big objects like buildings, it can be much larger, maybe 0.1 to 1mm (.005 to .05 in) or more.

• If you're going to be exporting your object for later processes, or are going to be doing very detailed renderings, you may need to tighten up the settings a bit, depending on where it's going and how precise the process is. For a stereolithography part, .01mm should still be fine for example, but for a good machined part, .001mm-.002mm is probably more appropriate.

It may seem a bit complicated at first, but after a bit of practice, you will find a few standard settings that work for you in most situations. These settings can even then be programmed into a macro or script to quickly launch the meshing of your objects with the desired characteristics.

Sometimes, you may find that even with the settings guidelines above, you are still not getting good results. The meshing in Rhino V5 has been completely re-written and in most cases produces much better results than earlier versions; but it may not handle all cases perfectly. If you find meshing problems you can't resolve, please report them on the Rhino support forum or send them to McNeel tech support.

Some problems may be caused by the mesher's reaction to models that have hidden geometric flaws. If this is the case, only way to correct them may be to do some reconstruction on the model. The flaws are often located close to where the visible mesh errors show up.

While these conditions don't always cause problems meshing, they have been known to do so in the past, so it's worthwhile checking if you are having difficulties.

• Bad objects. While they don't always result in mesh problems, these are easy enough to track down, so it's a good place to start. If you find one, try hiding it. If your problem disappears, then perhaps all you need to do is fix the object (make it valid) and you'll be good to go.

• Long, skinny surfaces. Difficult cases for the mesh engine in V4, this has been vastly improved in V5 and no longer pose a problem.

• Joined tangent lines and arcs that have been extruded or revolved. Example - extruding a rounded rectangle. This forms a single surface with internal G1 areas, which the mesher struggles with. Solution: Explode the curves before extruding, or use Split > Isocurves at the G1 spots to create a structure with separate joined tangent surfaces instead of one single one. In the case of the extruded rounded rectangle, you will have eight joined surfaces, not one. In V5, you can use the Extrude command option SplitAtTangents=Yes to automatically split the resulting extrusion.

• Kinked surfaces. Usually caused by having CreaseSplitting (native in V5 or V4 add-on) set to No, or using MergeSrf Smooth=No on surfaces that are not at least tangent to each other. In this case, again, it is better to have multiple joined surfaces instead of one kinked one. Use Surface edit tools > Divide surface along creases or Split > Isocurves at the kinked spots to split these types of surfaces up into separate parts.

• Triangular surfaces with holes This is a known bug in Rhino V4. The hole would be present in wireframe mode, but invisible in shaded mode. A “Custom” mode was required to render these surfaces correctly. This has been fixed in V5!