In my years of experience with BRL-CAD, I have used the combination for one thing. That is to group things using Boolean operations that can then be placed within a region. A combination does not have any material properties or ID number assigned to it, making it ideal for being placed into a region. Since the region does have material properties and an ID number, it is bad modelling practice to place one region into another. I primarily use combinations when I need to cut a specific shape out of another solid. I can create the shape using the combination, and then subtract it from the solid within a region.
In short, combinations can be unioned, subtracted, and intersected within a region. Robert Anderson -----Original Message----- From: B.V. Raghav [mailto:bvrag...@iitk.ac.in] Sent: Thursday, December 17, 2015 4:53 AM To: brlcad-users@lists.sourceforge.net Subject: [brlcad-users] Difference between regions and combinations Hi, I am an architect, who wants something more than what the proprietary modeling softwares offer. And my quest has led me to pursue using BRL CAD. I have little experience in programming, though I am comfortable coding simple scripts. That said. There is a fundamental question regarding using BRL-CAD and its concepts. Most importantly, the BRL-CAD offers an object hierarchy using a Binary tree, (broadly speaking, a Directed Acyclic Graph) and its algorithms. The primitives, combinations, regions and assemblies are the names we prefer to use in order to point to a specific node of the hierarchy. Primitives, represent leaves of the hierarchy. The two references appended in the mail clarify a lot about the regions and combinations, from the user's perspective. Summarily, I believe that: 1. Combinations are like logical groups, more for the clarity of the user, and primarily intended to store the structure and its implicit transformation matrices. 2. Regions are like physical groups, that can be thought of as an object with one color. Example, to create a wooden table. All the parts of a wooden table can be put together as a region. Along with it there can be subparts of the table that logically grouped into a combination, namely legs, ties (top and bottom), top and so forth. *TODO* I shall try to model and share the example. Please add to my understanding of BRL-CAD wherever necessary. -- (B.V. Raghav) Ph.D. Student, Design Programme Indian Institute of Technology Kanpur Ph: +91-9450988137 Thanks, r References: file:///usr/brlcad/share/doc/html/books/en/BRL-CAD_Tutorial_Series-VolumeIII.html#volIIIorganizing file:///usr/brlcad/share/doc/html/books/en/BRL-CAD_Tutorial_Series-VolumeII.html#boolean_tools -- (B.V. Raghav) ------------------------------------------------------------------------------ _______________________________________________ BRL-CAD Users mailing list brlcad-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/brlcad-users
