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, see this page. –Mitch 16.01.2013
The controls for the Render Mesh (display mesh) settings are part of the .3dm file's properties. In Rhino for Windows they area at File > Properties > Mesh or Tools > Options > Mesh. In Rhino for Mac they are at File > Settings > Mesh.
They are generally set globally for the whole model, but from V4 on, including Rhino for Mac, you can also override them on a per-object basis via the Properties panel.
Rhino offers you two standard settings, Jagged and Faster and Smooth and Slower, as well as Custom, which lets you access the detailed controls.
If you really want to control your meshing process, here is where you need to start!
When you check Custom in Rhino 5 (Mac or Win) you are first presented with a simple slider controlling the Density setting. Moving it to the left will result in fewer polygons and a coarser mesh, to the right in more polygons and a finer mesh.
If you then push the Detailed Controls button in Windows Rhino, or the little down arrow in Mac Rhino, it reveals 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.
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).
|Maximum aspect ratio||0.0|
|Maximum edge length||0.0|
|Maximum distance edge to surface||see below|
|Minimum initial grid quads||16|
Refine mesh checked
Jagged seams unchecked
Simple planes unchecked
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 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).
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 5 was completely rewritten and in most cases produces much better results than earlier versions, but it may not handle all cases perfectly. Meshing is being continually improved. If you find meshing problems you can't resolve, please report them on the Rhino support forum or send them to McNeel tech support.
The mesher's reaction to models that have hidden geometric flaws may cause some problems. The 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.
These conditions don't always cause problems meshing, but they have been known to do so in the past, so it's worth checking if you are having difficulties.