Faceted Radial Geometry

Introduction

Faceted radial geometry can often be seen in illumination systems where an entirely smooth surface is not required in order to achieve the desired effect. As of the date of the this article, FRED does not have a ready made primitive to create faceted radial geometry, but the flexibility of the existing surfaces within FRED does permit creating such shapes. The following example creates a 'Birdcage Parabolic Reflector', whose end result looks like so:

To create such a shape requires the use of Custom Elements, Curves, and the Ruled Surface. The completed example FRED file is provided at the end of this article.

Creating the First Element

First it is recommended to create a Sub-Assembly for the finished component, and within this create a Custom Element for the necessary curves. Curves can be added to the Custom Element from the R-Click menu. The First Element for the Birdcage Parabolic Reflector looks like so:

And is defined with the following four curves:

And these four curves are joined into a single "Base Curve" with the Composite Curve:

Creating the other Elements

With the First Element made creating the others is a simple matter of copy/pasting the First Element back into the sub-assembly and rotating the new elements into position. In this example the hexagonal cross section requires 6 elements with rotations about X axis of 0, 60, 120, 180, 240, and 300 degrees. The rotation for Element 2 is shown below:

And the finished "Birdcage" of six elements looks like so:

Skinning the Surfaces

The final step is to skin (or fill) the space between the elements. For this another custom element is added and within this the Ruled Surface is used to join the curves, e.g. for the Skin between Elements 1 and 2 we join the Base Curves of those two elements together with the following settings:

Not forgetting to set the trimming volume to be sufficient to cover the surface:

Which gives the first skinned surface:

And the process is repeated to add further ruled surfaces (shown as not traceable in the above) to fill in the remaining gaps.

FRED File: Birdcage-Parabolic-Reflector.frd