BOG - A Better Optimizer for GemRay
by Tom Herbst

Version 1.2 - 15 August 2005


Click here to jump to the online tutorial and documentation.

What is BOG?

BOG is a Windows-based program to assist the gem faceter in selecting optimal pavillion and crown angles, based on a series of user-specified criteria. These criteria include:

- Gem brightness
- Illumination response
- Tilt performance
- Sparkle
- Fire or dispersion

BOG also provides a "PlayPen" in which to experiment with different gem parameters and see their effect on optical performance. The PlayPen provides a user-friendly interface to the GemRay program, including interactive entry of parameters, storage and comparison of different results, and automatic evaluation of tilt performance.

There is also a "Merit Function Mapper" which lets you graphically explore a range of pavillion and crown angles for best performance. This mode lets you instantly see the raytraced image, ISO brightness, etc. as you click around on various angle combinations.

See the screenshots below for an impression of how BOG works.
Follow this link to the online tutorial and documentation.

BOG PlayPen rendering of the "Trouble" (with Tribbles) gem design.

A 15 mm, 8 carat Amethyst cut in the "Trouble" design.


What does BOG do?

What does BOG NOT do?

BOG is essentially an intelligent front-end to the GemRay program written by Robert W. Strickland.

Based on a user-specified merit function BOG calls GemRay repeatedly, varying the gem angles to achieve the best possible performance.

BOG also allows interactive exploration of the effects on a gemstone of facet angles, material properties, and colour.

BOG doesn't do any ray trace calculations itself. Rather, it calls the GemRay program with appropriate parameters and uses the results in the output file (GemRay.log).

BOG also doesn't affect the original .GEM files. In fact, for safety, BOG works on a copy of the gem file. This means that you will have to manually enter/transpose the angles. A complete description of this process appears here.


BOG Screenshots (from v. 1.0)


BOG is useful when transposing a published design to a material with a different refractive index. It also lets the user trade-off different types of performance. For example, the faceter may choose to sacrifice some face-up brightness in order to gain better brightness when tilted. It also helps the user find the best alternate design, given the shape of the gem rough, internal flaws, etc.

Click on the image at right to see a screen shot of the Optimization window.








Click on the image at left to see a screen shot of the PlayPen window. This example shows a comparison of the same design cut in quartz (top) and cubic zirconia (bottom). Note the coloured streaks corresponding to dispersion or "fire" in the raytraces.







Merit Function Mapper

Click on the image at right to see a screen shot of the Merit Function Mapper window. In this example, the user is exploring gem angle combinations for a Long and Steele "Superpear" design cut in Peridot.








The best way to learn about BOG is to try it. Follow this link to online documentation, including a multi-part BOG tutorial

Documentation maintained by Tom Herbst. Last modified 17-Aug-2005