Re: [brlcad-devel] Tessellation of NURBS surface

[Christopher S. M. <br...@ma...>]

>>    Because I have already drafted a rough implementation of plate mode
>> NURBS ray tracing, and it works well for me now, I also put all the tests on
>> my blog, please check it, if you have any issues, please let me know and I
>> will make proper refinement, it will be much grateful. :-)

Why do you say it’s “rough"? :)

The blog progress looks great, but the test cases are limited.  In addition to validating that you’re creating the “plate” correctly like Cliff mentioned, with gqa, it would be good to see a lot more variety of surfaces before moving on to anything else.  For example, surface with a hole trimmed, two surfaces joined at a seam, a high-order surface, a simple flat surface with varying thicknesses, etc.

As the ultimate purpose for plate-mode NURBS is to support importing non-solid entities, the next step once it’s all working will be to get the 3dm-g and step-g converters updated.  From there, we’ll need commands to detect when something is marked solid (but is not) or plate (and could be solid), so we can start working on geometry reporting and cleanup procedures accordingly. 

>>    So, recently, I want to shift my attention to the tessellation of NURBS,
>> it is much more challenging. Because after my research, I find that there
>> are several related methods that can be used for the purpose. There also
>> exists an old implementation in BRL-CAD(nurb_tess.c), it is a kind of
>> mapping from triangulation of 2D parameter space to 3D surface space within
>> given approximation errors bound(I have summerized this method on my
>> blog.:-) ), it is a simple and effective method.

Glad you found the old method and there’s also a newer method in the brep code.  Once import and ray tracing work is complete, moving onto tessellation makes great sense as it’s needed for export.

Cheers!
Sean